# openQCM FAQ > Source page: https://openqcm.com/faq > Markdown version for AI agents and readers of plain text. Site guide: https://openqcm.com/llms.txt · Everything in one file: https://openqcm.com/llms-full.txt 354 answers from the openQCM team, grouped by topic. Each answer says which instruments it applies to. ## QCM theory & basics ### What are the Sauerbrey constants for openQCM quartz sensors? *Applies to: all instruments* For the standard 10 MHz AT-cut sensors, use these values in the Sauerbrey equation: - Active electrode area: *A* = 0.196 cm² (back electrode Ø 5.0 mm on the current AT5/AT10 crystals; older crystals may differ) - Quartz density: *ρ* _Q = 2.648 g·cm⁻³ - Shear modulus: *μ* _Q = 2.947 × 10¹¹ g·cm⁻¹·s⁻² - Shear-wave velocity: *v* _Q = 3.336 × 10⁵ cm·s⁻¹ From these you can compute mass responsivity, surface-mass responsivity and the mass saturation limit. See the [Sauerbrey equation wiki](http://quartzcrystalmicrobalance.org/index.php?title=Sauerbrey_Equation) for the full derivation. Source: https://forum.openqcm.com/d/4-some-operational-questions ### Does the quartz resonance frequency have to match the oscillator driver frequency? *Applies to: all instruments* Not necessarily — it depends on the excitation method. Wi2, TWIN, SpaceBug and the original openQCM use a **Pierce oscillator** that self-oscillates with the crystal, so the resonance is found automatically. Q-1 and NEXT drive the crystal passively with a **DDS** and sweep a band around each resonance, so the sweep window must contain it. A third option is impulse excitation, which nominally excites all frequencies at once. Source: https://forum.openqcm.com/d/14-quartz-crystal-fand-oscillator-driver-frequency ### Is there a maximum mass the sensor can measure? What is the loading range? *Applies to: all instruments* The nominal mass-saturation limit for a rigid, uniform film is roughly *f* /100 of the resonance frequency. For a 10 MHz sensor this gives about **0.44 mg/cm²** . In liquids the picture is more complex: the acoustic penetration depth in water at these frequencies is about **250 nm at 5 MHz and 180 nm at 10 MHz** , so a frequency–mass relation is only accurate for layers thinner than this, and only when the sample behaves rigidly. Thick droplets or soft layers introduce viscoelastic effects that break the simple Sauerbrey relation. Source: https://forum.openqcm.com/d/13-operation-range ### Why does my frequency increase instead of decrease during a measurement? *Applies to: all instruments* A rising frequency generally indicates a **loss of mass** from the sensor. Temperature is rarely the cause for large shifts (e.g. ~1000 Hz). In swelling-polymer or solvent-uptake experiments, the swelling process can also introduce **viscoelastic effects** that alter the expected frequency behaviour. Rule out desorption, solvent-concentration changes and temperature first, then consider viscoelasticity. Source: https://forum.openqcm.com/d/3-frequency-behavior ### How does temperature affect the frequency, and how do I compensate for it? *Applies to: all instruments* Every quartz crystal has its own temperature–frequency dependence, well described by a **third-degree polynomial** , because the wave propagation through the crystal varies with thickness and cut. The coefficient differs from crystal to crystal, so a single global value is not sufficient. The robust approach is to **build a T–frequency calibration curve** with a clean sensor in your actual medium (air, vacuum or liquid), then subtract that effect from your data. If you see a time lag between the temperature and frequency readings (thermal inertia between the two sensors), shift the temperature trace to align them — users typically recover R² > 0.99 after this correction. In a complete Q-1 device the temperature sensor sits just 1–2 mm below the quartz. Source: https://forum.openqcm.com/d/31-temperature-compensation-for-measured-frequency-and-dissipation-values ### Why does my frequency baseline drift sometimes? *Applies to: all instruments* In a well-set system, drift is usually negligible. When it occurs, the most common causes are **temperature variations** , humidity, swelling of the O-ring, or mechanical stress on the sensor (including pogo-pin pressure). openQCM embeds a temperature sensor precisely so you can check the thermal conditions in real time. Source: https://forum.openqcm.com/d/18-openqcm-q-1troubleshooting ### How do the Q-1 and NEXT measure frequency and dissipation? *Applies to: Q-1, NEXT* Q-1 and NEXT have no oscillator and do not use ring-down. Their electronics work as a **scalar network analyser** that interrogates the crystal passively: 1. An AD9851 **DDS** steps the excitation frequency across each resonance. 2. An AD8302 **gain/phase detector** records the amplitude transmitted through the crystal at each step, so the resonance curve is rebuilt point by point and kept in a buffer. 3. A **peak-detection** algorithm takes the frequency of the highest point as the resonance frequency. There is no curve fitting. 4. The curve width, read where it crosses a cut-off set a calibrated amount below that harmonic’s own peak, gives the dissipation. The sweep is repeated on the fundamental and on each available odd overtone. Because the crystal is measured on its own, no external oscillator circuit influences the result. Source: openQCM Measurement Methodology (Q-1 and NEXT), p.4-5, 10-11 ### Is the dissipation reported by Q-1 and NEXT the same as D = 1/Q? *Applies to: Q-1, NEXT* Not exactly. The textbook definition takes the half-power (−3 dB) bandwidth: D = 1/Q ≈ Δf/f_r. At higher overtones the peak is lower, and a fixed −3 dB level would fall into the noise. openQCM therefore sets, for each harmonic *n* , a cut-off at A_peak − ΔA_n, where ΔA_n is fixed during instrument calibration, and reports D_n = Δf_n/f_r,n. This **instrumental dissipation** is systematically related to, but not numerically identical to, the canonical D. Under fixed conditions it tracks changes (ΔD) faithfully. To compare absolute values with the literature, apply a correction factor or calibrate against a reference. For orientation, D is typically about 10^−6 in air and 10^−4 in liquid. The NEXT software shows dissipation in ppm (1 ppm = 10^−6). Source: openQCM Measurement Methodology, p.5-11; openQCM NEXT user guide, p.30 ### How do I read multi-harmonic data: is my layer rigid or viscoelastic? *Applies to: NEXT, Q-1* Normalise each frequency shift by its overtone number and compare the overtones: - **Rigid film** (Sauerbrey applies): Δf_n/n is about the same on every overtone, and the dissipation stays low and nearly constant across harmonics. - **Viscoelastic layer** (soft films, hydrated layers, cells, many polymers): Δf_n/n spreads between overtones and dissipation rises. The Sauerbrey equation then underestimates or misrepresents the mass, and a viscoelastic model is needed. The overtones also probe different depths. Lower harmonics penetrate further and sense the whole film; higher harmonics are more sensitive to the region near the surface. In liquid the penetration depth decreases as frequency increases. In soft films it is an effective interaction region rather than a sharp thickness. Source: openQCM Measurement Methodology, p.12-13 ### How do the frequency-only devices (Wi2, TWIN, SpaceBug, Holder) measure, and what does 1 Hz correspond to? *Applies to: Wi2, TWIN, SpaceBug, Holder* These devices keep the crystal oscillating in a **Pierce oscillator** built on an SN74LVC1GX04 inverter. A hardware counter counts the oscillator output over a fixed gate, typically **1 s** in the sample firmware, so each reading is an integer number of hertz. The Holder carries the oscillator only: the counter is in your own electronics. They report frequency, not dissipation. For a rigid film, the Sauerbrey constants give about **4.4 ng/cm² per hertz** at 10 MHz and about 17.7 ng/cm² at 5 MHz. Over the 0.196 cm² active area of current crystals, 1 Hz at 10 MHz is roughly 0.9 ng. These are our calculations, not manufacturer specifications. Temperature, mounting stress and the medium still set the practical noise floor. Source: openQCM_Wi2-user_manual, p.5; openQCM_TWIN_User_Manual, p.12, 24; openQCM SpaceBug, p.10, 31-39; openQCM Holder, p.7 ### How do I turn frequency shifts into mass or film thickness, step by step? *Applies to: all instruments* The software logs frequency and dissipation, not mass. For a thin, rigid, uniform film, convert with the Sauerbrey equation, Δm/A = −C · Δf_n/n: 1. **Baseline:** Δf_n is each reading minus the stable baseline of the same harmonic, taken in the same medium. 2. **Normalise:** divide by the overtone number n (1, 3, 5…). The software does not do this for you. 3. **Constant:** use C for the nominal fundamental, even for overtones: about 17.7 ng·cm⁻²·Hz⁻¹ at 5 MHz and 4.42 ng·cm⁻²·Hz⁻¹ at 10 MHz. Electrode coatings of a few hundred nanometres do not change C. 4. **Absolute mass:** multiply by the active area, 0.196 cm² on current AT5/AT10 crystals. That is about 3.5 ng/Hz at 5 MHz and 0.9 ng/Hz at 10 MHz. 5. **Thickness:** divide the areal mass by the film density. Do this in a spreadsheet or with the online openQCM Sauerbrey calculator. Before trusting the result, check that dissipation stays low and that Δf_n/n agrees across overtones. If not, the film is not rigid. Source: openQCM support archive (43 threads) ### Does it matter where the mass sits on the crystal? *Applies to: all instruments* Yes. The mass-sensitive region is where the front and back electrodes overlap: on current AT5/AT10 crystals, the Ø 5.0 mm back electrode, 0.196 cm². Within it, sensitivity is not uniform. It is highest at the centre and falls smoothly, roughly as a Gaussian, to nearly zero at the electrode edge. - The Sauerbrey equation assumes mass spread evenly over the active area. A small spot at the centre gives a larger shift than the same mass spread uniformly, so the apparent sensitivity is higher than nominal. - The same spot placed off-centre gives a smaller shift. - Material well outside the active area, such as an edge bead, contributes little. - If deposits form on both faces, for example during exposure in air, the shift reflects the total on both faces. In liquid cells only the top face should be wetted. For quantitative work, deposit a uniform layer that covers at least the whole active area. Place droplets or spots at the centre and calibrate with a known amount of the same material. Source: openQCM support archive (17 threads) ### What frequency shift should I expect from air to water, and what if mine is different? *Applies to: all instruments* Going from air to a liquid is not a Sauerbrey mass effect. A thin layer of liquid is dragged by the shear motion, which lowers the frequency and raises the dissipation. The Kanazawa–Gordon relation gives Δf = −f_0^3/2 √(ρ_Lη_L / (π ρ_q μ_q)). For pure water at room temperature expect roughly −0.7 kHz at 5 MHz and roughly −2 kHz at 10 MHz; the exact value depends on temperature. Buffers such as PBS give slightly larger shifts because of their higher density and viscosity. - A much **smaller** shift usually means air or bubbles left in the cell, a poorly wetted (contaminated) surface, or a cover pressing too hard on the crystal. - A much **larger** drop, strong noise or a frequency falling to zero suggests liquid under the crystal or loss of the resonance. - A shift consistently a fixed percentage above theory is discussed in the FAQ on the Kanazawa–Gordon prediction. Always take the baseline in the liquid you will measure in. Source: openQCM support archive (13 threads) ### Can I measure the viscosity of a liquid with a QCM? *Applies to: Q-1, NEXT* Yes, as density × viscosity. For a Newtonian liquid on one face of the crystal, the Kanazawa–Gordon relation gives Δf_n = −√n · f_0^3/2 · √(ρ_Lη_L / (π ρ_q μ_q)), where ρ_L and η_L are the liquid density and viscosity. When one liquid replaces another, the shift depends on the difference in √(ρη). Dissipation rises too, and for an ideal Newtonian liquid ΔD ≈ 2|Δf|/f; a clear deviation from that ratio means something is happening at the surface. - Use the Q-1 or NEXT: the Wi2 oscillator can stop in viscous liquids. - Viscosity depends strongly on temperature, so stabilise it (active control on the NEXT). Once stable, a reading takes only seconds. - Validate first with sucrose or glycerol solutions of known concentration; for large shifts, widen the sweep window. The QCM senses only the liquid within a few hundred nanometres of the surface, so it reports near-surface behaviour, not bulk rheology of non-Newtonian samples. Source: openQCM support archive (5 threads) ### What is the smallest mass change I can detect? *Applies to: all instruments* The detection limit is the frequency noise of your setup multiplied by the mass sensitivity. A common criterion counts a shift as reliable when it is about three times the baseline standard deviation. Example (calculated): a 10 MHz crystal (4.42 ng·cm⁻²·Hz⁻¹) with 1 Hz of baseline noise gives about 13 ng/cm², or about 2.6 ng over the 0.196 cm² active area. A 5 MHz crystal is four times less sensitive per hertz. For reference, the typical frequency noise of the Q-1 and NEXT is 0.1 Hz in air; the Q-1 acceptance test allows up to 2.0 Hz in static water at 10 MHz. Picogram detection is beyond QCM. To approach the instrument limit: - stabilise the temperature and let the system equilibrate; - stop the pump during readings and remove bubbles; - avoid vibration and electromagnetic interference; - return to the same buffer before and after binding; - average the data, at the cost of time resolution. Long-term drift often matters more than short-term noise. A QCM measures mass bound to the surface, not concentration in solution, so a biosensor limit also depends on the surface chemistry. Source: openQCM support archive (25 threads) ### What is dissipation, and how do I convert it to bandwidth or Γ? *Applies to: Q-1, NEXT* Dissipation D is the energy lost per oscillation cycle relative to the energy stored, D = 1/Q. A sharp, tall resonance has high Q and low D; a broad, damped one has low Q and high D. Typical values are of the order of 10⁻⁶ in air and 10⁻⁴ in liquid. The NEXT software shows D in ppm (10⁻⁶). A rigid layer barely changes D, while a soft, swollen or loosely bound layer raises it. Watching D next to frequency tells you whether a shift can be read as mass, which is why it matters for liquids, biosensing, cells and polymers. The Wi2 measures frequency only. The Q-1 and NEXT report D = w/f_r, where w is the peak width at a calibrated level. So the full width is w = D·f_r and the half-width is Γ = D·f_r/2. Because the width is not taken exactly at half power, absolute widths may need a correction before comparison with instruments that report Γ; changes (ΔD, ΔΓ) are reliable. The dissipation definition also changed between Q-1 software versions, so note the version when comparing absolute D. Source: openQCM support archive (11 threads) ### How does openQCM differ from ring-down QCM-D and from oscillator-based QCMs? *Applies to: Q-1, Wi2, NEXT* - **Ring-down** instruments excite the crystal, switch the drive off and analyse the free decay to obtain frequency and D. - **Oscillator** devices (Wi2, TWIN, SpaceBug, the Holder with your own counter) keep the crystal in a Pierce oscillator and count its fundamental frequency over a gate, typically 1 s. They are simple, low-power and easy to replicate, but give no dissipation and no overtones, and the oscillation can stop under heavy damping such as viscous liquids or thick soft coatings. - **Q-1 and NEXT** use a scalar network analyser. A DDS (AD9851) sweeps each harmonic and a gain/phase detector (AD8302) records the transmitted amplitude. Frequency comes from peak detection, with no curve fitting, and dissipation from the peak width at a calibrated level. The crystal is measured passively, outside any feedback loop, so heavily damped resonances can still be tracked. Frequency shifts are directly comparable between techniques, and ΔD trends agree. Absolute D from the Q-1 and NEXT is an instrumental value, and its definition changed across Q-1 software versions, so comparison with ring-down values needs a correction factor or a reference measurement. Source: openQCM support archive (37 threads) ### How should I interpret a dissipation change relative to the frequency change? *Applies to: Q-1, NEXT* Compare ΔD with Δf, or plot ΔD against −Δf (a D–f plot, which removes time): - **Rigid mass:** frequency drops, D stays almost constant, and Δf_n/n is the same on all overtones. A low, flat D–f slope. - **Newtonian liquid change:** ΔD ≈ 2|Δf|/f, with f the resonance frequency of the harmonic used. - **Soft or viscoelastic layer:** ΔD clearly larger than 2|Δf|/f, or a steep D–f slope. The layer is changing its structure (swelling, hydration, growth of soft biomass), not just its mass. Changes of slope or loops mark transitions such as reorganisation. Example from a bacterial growth run at 10 MHz: Δf ≈ −140 Hz and ΔD ≈ 90 × 10⁻⁶, against 2|Δf|/f ≈ 28 × 10⁻⁶, a strongly dissipative layer. The time evolution of both signals often says more than the overall change. Because openQCM D is an instrumental value, use these ratios for trends and comparisons on the same instrument rather than as absolute thresholds. Source: openQCM support archive (4 threads) ### Does the openQCM software fit viscoelastic models to my dissipation data? *Applies to: Q-1, NEXT* No. The software acquires frequency and dissipation for each harmonic in real time and saves them as CSV files; it does not fit a physical model. - **Qualitative analysis** is often enough: comparing ΔD between samples or conditions shows whether a layer becomes softer, more hydrated or more rigid, and a ΔD versus Δf plot separates mass uptake from structural change. - **Quantitative values** such as thickness, shear modulus or viscosity need a viscoelastic model, for example the Voigt–Kelvin model of Voinova et al. ( *Physica Scripta* 59, 391, 1999), fitted to frequency and dissipation on several overtones. Researchers do this on the exported files with their own scripts or third-party open-source QCM-D modelling tools. Results depend strongly on the model and its assumptions. openQCM dissipation is measured from the peak width at a calibrated level and tracks changes reliably. Before fitting absolute values, apply a correction factor or calibrate against a reference, and record the software version, since the D definition changed between Q-1 versions. Source: openQCM support archive (5 threads) ### Which overtones should I use, and how many do I need for viscoelastic modelling? *Applies to: NEXT, Q-1* Overtones are odd multiples of the fundamental: 5, 15, 25, 35 and 45 MHz for a 5 MHz crystal. In liquid, lower overtones probe deeper and higher overtones are more surface-sensitive. Higher overtones have smaller peaks, so their noise, especially in D, is usually larger. - **Rigid film:** one harmonic is enough. A low or middle overtone, often the 3rd, is a good compromise. The fundamental is the mode most affected by mounting stress such as O-ring pressure, and often behaves as an outlier. - **Viscoelastic film:** a model has at least three unknowns (thickness, and storage and loss modulus or viscosity), so you need f and D on at least three overtones, for example n = 3, 5 and 7, recorded throughout the run. With 5 MHz crystals on the NEXT, the 3rd, 5th and 7th are the most reliable, and the 9th is useful as a cross-check. Different magnitudes of Δf and ΔD between overtones are normal, not a calculation error; compare Δf after dividing by n. The Q-1 follows one harmonic per session, so for multi-harmonic work use the NEXT. Source: openQCM support archive (20 threads) ### Why does my Sauerbrey mass differ from the value I get with another technique? *Applies to: all instruments* Sauerbrey holds only for a layer that is thin, rigid, uniform and firmly attached, so that it moves as part of the quartz. Common reasons for a systematic difference: - **Viscoelastic or thick layers** (polymers, hydrated proteins, cells, oils) lag behind the oscillation, so part of the mass is missing from the frequency response. - **Coupled water:** in liquid, trapped or hydrodynamically coupled solvent is sensed as mass, so the QCM mass can exceed a dry-mass value from, for example, ellipsometry. - **Poor adhesion or uneven coverage,** especially spots or deposits near the electrode edge. - **Temperature changes,** or changes in bulk density and viscosity during the run. - **Wrong area** in the calculation: use 0.196 cm² for current crystals. Check rigidity first: if Δf_n/n is about the same on all overtones and D stays low, Sauerbrey applies. For dry films, an overtone such as n = 3 is more reliable than the fundamental. Otherwise fit a viscoelastic model to multi-overtone data. An empirical calibration factor against an independent method is valid, but only for that sample type and protocol. Source: openQCM support archive (21 threads) ### Why does the same crystal show a different frequency on different instruments? *Applies to: all instruments* The instruments read the resonance in different ways. - **Oscillator electronics** (Wi2, the Teensy shield, the Holder with an oscillator) make the crystal part of a circuit that must satisfy the oscillation conditions. The load capacitance of that circuit pulls the frequency slightly away from the crystal's series resonance. - **Sweep electronics** (Q-1, NEXT) interrogate the crystal passively and report the frequency of maximum amplitude, which is closer to the series resonance. Absolute values therefore differ by a small offset, and even two units of the same type can differ slightly because of component tolerances. Under the same conditions they measure comparable frequency changes, which is what matters for mass and dissipation analysis. Always work with shifts relative to a baseline recorded on the same instrument with the same crystal, and do not mix absolute frequencies from different instruments in one analysis. Source: openQCM support archive (1 thread) ### Can I get the full electrical impedance of the crystal from the Q-1 or NEXT? *Applies to: Q-1, NEXT* Not directly. The Q-1 and NEXT are scalar network analysers. A DDS synthesiser drives the crystal, and a gain/phase detector (AD8302) measures the magnitude ratio and phase difference between the drive and the transmitted signal as the frequency is swept. The software uses the amplitude curve to derive resonance frequency and dissipation. - The raw sweeps (frequency, amplitude in dB, phase in degrees) can be exported for your own analysis; on the Q-1, enable the sweep-file export option. - The instrument does not perform the open/short/load calibration of a vector network analyser, so real and imaginary impedance values need your own calibration. Some researchers have derived conductance spectra this way. - Phase is recorded but not used for the measurement, and its extreme lies slightly off the amplitude peak. For true impedance spectra, connect the crystal through a holder to an external impedance analyser. Source: openQCM support archive (3 threads) ### Does gravity or sensor orientation affect QCM measurements? *Applies to: all instruments* No. The QCM response comes from the shear vibration of the crystal and does not depend on gravity, so the sensor works in any orientation, including in microgravity. The SpaceBug, for example, was designed for small satellites. Orientation matters only for how the sample reaches the surface: - Particles or cells that sediment deposit more on an upward-facing sensor, so the signal may reflect sedimentation as well as binding. - To measure adhesion or deposition rates without sedimentation, mount the sensor facing down or vertically. - In liquid cells, check that bubbles do not collect on the crystal in the chosen orientation. A reference crystal under the same conditions allows a differential measurement that removes common effects such as temperature. Source: openQCM support archive (2 threads) ### Does the crystal vibration affect my sample, and can I use magnets near the sensor? *Applies to: Q-1, Wi2* The crystal surface moves with a shear amplitude of only a few nanometres, largest at the electrode centre. Its effect on processes such as migration, leaching or binding is generally negligible, apart from a possible minor influence on the liquid boundary layer. The Q-1 and Wi2 sensor module is made of non-magnetic materials (nylon, PMMA or PTFE), but it contains small neodymium magnets that hold the top cover closed and keep the temperature sensor against the crystal. If you plan to apply an external magnet, for example to pull magnetic nanoparticles toward the surface: - check experimentally, in your geometry, how much field reaches the sensor; - check whether the closure magnets distort it or are pulled by your magnet; - run a control without particles to see any direct effect on the baseline. Small particles far from the closure magnets should be affected very little. Source: openQCM support archive (3 threads) ### My frequency goes up when I add material. What should I check? *Applies to: all instruments* A rigid mass always lowers the frequency, so a rise during adsorption points to something else. Work through this list: - **Mass loss:** solvent evaporation, desorption, or shrinking of a coating. - **Viscoelastic or low-density layers in liquid:** a very lossy, thick layer, or one less dense than the medium, can give positive or missing-mass shifts. Check dissipation and several overtones. - **Overloaded coating:** a crystal coated close to its load limit becomes unstable and responds abnormally. Start from a lighter coating. - **Setup artefacts:** a crystal mounted upside down, a lever or cover pressure different from the one used at calibration, temperature changes, or a leak. - **Bulk changes:** a liquid of lower density or viscosity than the baseline liquid also raises the frequency. Run a clean crystal under the same conditions as a control before you interpret the sign of the response. Source: openQCM support archive (6 threads) ### In practice, how much total frequency shift can a crystal handle? *Applies to: all instruments* The nominal limit for a rigid film is a shift of about 1 % of the fundamental (f_0/100): about 50 kHz at 5 MHz and 100 kHz at 10 MHz (see the FAQ on maximum mass). The usable range is several times smaller: - For reliable Sauerbrey data, support experience suggests keeping the total shift within about 0.1–0.2 % of f_0, roughly 5–10 kHz at 5 MHz or 10–20 kHz at 10 MHz. - Soft, viscous or wet layers damp the resonance much earlier, and discrete particles also saturate early. - The limit is per unit area: concentrating the load in a small spot saturates sooner. - Every coating counts. Recalibrating after coating re-centres the sweep on the new peak but does not give back the capacity the coating used. Near saturation the peak broadens and flattens, the frequency jumps or falls to zero, or the software cannot find the peak. Very large shifts may also leave the sweep window, which can be widened. For heavy loads use 5 MHz crystals and thinner films; the Q-1 and NEXT track a damped resonance better than oscillator devices such as the Wi2. Source: openQCM support archive (27 threads) ### Can a QCM weigh a droplet, a particle or a gram-scale sample? *Applies to: all instruments* No. A QCM is extremely sensitive only to mass deposited as a **thin, rigid, uniform film** firmly coupled to the crystal. Discrete or bulk samples fail for several reasons: - **Saturation:** the linear response covers at most micrograms per square centimetre. Tens of micrograms concentrated on the electrode, let alone grams, are far beyond it. - **Non-uniform sensitivity:** it is highest at the centre and near zero at the edge, so the reading depends on where an object sits. - **Poor coupling:** a solid resting on a few contact points acts more like a damper than a mass. Fixing it with a soft material makes this worse. - **Penetration depth:** in liquid only the first few hundred nanometres are sensed, so a thick drop is seen through its viscosity, not its weight. Use an analytical ultra-microbalance instead. A QCM can still help when the material can be deposited as a thin film, or when the mass lost by a sample lands on a nearby crystal, as in outgassing or evaporation monitoring. Source: openQCM support archive (5 threads) ### How far into a liquid does the QCM sense, and does the liquid height matter? *Applies to: all instruments* In liquid the shear wave decays within the penetration depth δ = √(η/(π f ρ)): about 250 nm at 5 MHz and 180 nm at 10 MHz in water. It shrinks at higher overtones in proportion to 1/√n, so higher harmonics probe closer to the surface. - Only material within this region affects frequency and dissipation. Beyond it the liquid behaves as a semi-infinite medium, so the liquid height above the crystal does not matter once the electrode is fully covered. - Bulk events far from the surface, such as sedimentation or mixing, are seen only when they reach the surface region or change the density and viscosity of the liquid next to it. - Cells or soft layers thicker than δ are probed only partly. Comparing overtones gives a coarse depth profile. - The QCM reports near-surface properties, not bulk rheology. Very lossy samples, such as whole blood, can damp the resonance completely. In droplet-evaporation studies the signal is dominated by the contact line at the edge of the drop. Source: openQCM support archive (6 threads) ## Specs & compatibility ### Can I monitor multiple overtones simultaneously? *Applies to: Q-1, NEXT* The **Q-1** reads one overtone at a time: you choose the fundamental or an overtone and it follows that one. For multi-harmonic QCM-D we designed **[openQCM NEXT](https://openqcm.com/about-openqcm-next/)** : in Multiscan mode it sweeps the fundamental and all available overtones one after another and logs every harmonic in each cycle, about 1.4 s per overtone, so you see all of them through the whole experiment (plus active temperature control and an electrochemistry option). Source: https://forum.openqcm.com/d/21-monitoring-multiple-overtones-simultaneously ### Can the Wi2 give me the resonance peak and dissipation, like the Q-1? *Applies to: Wi2, Q-1, NEXT* No. The **[Wi2](https://openqcm.com/about-openqcm-wi2/)** is based on a Pierce oscillator and outputs **frequency only** . To obtain the full resonance curve, dissipation and overtone analysis you need the **[Q-1](https://openqcm.com/about-openqcm-q-1/)** or **[NEXT](https://openqcm.com/about-openqcm-next/)** , which sweep and reconstruct the resonance curve. Source: https://forum.openqcm.com/d/24-resonance-peak-with-wi2-software ### Can openQCM NEXT or Q-1 be used for electrochemical QCM (EQCM)? *Applies to: NEXT, Q-1* Yes. There is a dedicated **EQCM module** for each instrument: one for the **Q-1** and one for **NEXT** (the NEXT module is still an experimental prototype). The crystal’s top gold electrode is the working electrode; reference and counter electrodes go through the PTFE cover. You connect your own potentiostat, since the module has none built in. See the [NEXT EQCM module](https://openqcm.com/about-openqcm-eqcm-next/). Source: https://forum.openqcm.com/d/39-compatibility-of-openqcm-next-for-electrochemical-qcm-eqcm-experiments ### My Q-1 shows drift, a temperature rise on long runs, and evaporation with the PTFE cap. Is this normal? *Applies to: Q-1* Some **drift is normal** QCM behaviour and can come from humidity, temperature or O-ring swelling (these effects are also described in the Q-Sense E-series manual). For long runs with an open/PTFE pipetting cover, manage **solvent evaporation** deliberately — it changes the mass on the sensor and the local temperature. Stabilise thermally, minimise the open-air time, and use temperature compensation. Source: https://forum.openqcm.com/d/18-openqcm-q-1troubleshooting ### I built a custom unit with a DDS and AD8302 — how do I turn the impedance curve into a resonance peak? *Applies to: all instruments* The peak-shaped response comes from the **AD8302** gain/phase detector: it compares the signal from the DDS (INPB) against the signal from the quartz sensor (INPA). Feed both into the AD8302 as in its datasheet, then **process the output in firmware/software** to detect the peak and measure its width at a calibrated level below the peak (the Q-1 software uses peak detection with a calibrated cut-off per harmonic, not a curve fit). The openQCM Q-1 firmware and software are open-source, and we can share the Q-1 schematic so you can compare component values (input capacitors, buffer op-amps, etc.). Source: https://forum.openqcm.com/d/42-measurement-conversion ### Is openQCM a real, high-quality scientific instrument? *Applies to: all instruments* Yes. Although it is low-cost and open-source, its accuracy and stability are comparable to mainstream commercial QCM systems. openQCM is developed by a team with years of mass-sensor experience — including QCM calibration work for the **ESA-Rosetta** space mission and numerous scientific QCM/MEMS devices for space, biology and electrochemistry. ### Can I use openQCM in air or in vacuum? *Applies to: all instruments* Yes — it is designed for use in air, in liquid and in vacuum. To work in a gaseous environment, simply remove the magnetic sealing chamber; no further modification is needed. ### Is openQCM suitable for teaching and educational use? *Applies to: all instruments* Absolutely. Its affordability and ease of use make it an excellent teaching tool — for university courses or any level of school, it brings hands-on quartz-crystal-microbalance experiments within reach. ### What are the main technical specifications of openQCM NEXT? *Applies to: NEXT* openQCM NEXT uses a single quartz resonator sensor (5 MHz or 10 MHz, 14 mm blank diameter, wrapped single-sided contacting) with a frequency range of 1 to 50 MHz. It measures frequency and dissipation in multi-overtone mode via a network analyser interface, reading all available overtones in every multiscan cycle, about 1.4 s per overtone. The fluidic chamber volume is about 50 µl. The main unit measures (L × W × H) 20 × 8 × 4 cm and weighs 260 g. Source: openQCM NEXT user guide, p.9 ### Which overtones can openQCM NEXT measure? *Applies to: NEXT* openQCM NEXT operates in multi-overtone mode. With a **5 MHz** quartz it measures up to the **9th overtone** , and with a **10 MHz** quartz up to the **5th overtone** . Both frequency and dissipation are monitored in real time on the fundamental and the harmonic overtones. Source: openQCM NEXT user guide, p.9 ### What are the key specifications of the openQCM Q-1? *Applies to: Q-1* Key specifications include: - **Sensors** : single quartz resonator, 5 MHz and 10 MHz, 14 mm blank diameter, wrapped (single-sided) contact. - **Measurement chamber volume** : ~50 µl. - **Quantities** : frequency and dissipation; single overtones up to the 9^th overtone for 5 MHz sensors. - **Sampling time** : ~1.0 s per overtone. - **Dimensions** : 143.1 × 66.8 × 26 mm; weight 50 g. - **Microcontroller** : Teensy 3.6 (ARM Cortex-M4); powered by USB 5 VDC. Source: openQCM_Q-1-user_manual, p.36 ### What temperature and power limits must I respect with the Q-1? *Applies to: Q-1* The 3D-printed Nylon case is heatproof to **80°C** ; higher temperatures can significantly change material properties. The electronics components (e.g. the Teensy microcontroller and Q-1 shield) are rated for a working range of **-40°C to 85°C** . The device must be powered only at a continuous **5 VDC** via USB — using a different power supply will damage it. Source: openQCM_Q-1-user_manual, p.37 ### What are the main specifications of the Q-1 EQCM module? *Applies to: Q-1* Key e-QCM module specifications: - **Chamber volume** : ~15 ml. - **Materials** : PTFE (Teflon) reservoir and cover, FKM Viton O-rings, quartz cylinder, anodized-aluminium sensor holder, PLA plastic case. - **Dimensions** : 6 × 7 × 6 cm; weight ~90 g. - **Sensors** : single quartz resonator, 5 MHz and 10 MHz, 14 mm blank diameter, wrapped contact; multi-overtone (up to 9^th for 5 MHz, up to 5^th for 10 MHz). - **Sampling time** : ~1.0 s per overtone (openQCM Q-1, one overtone at a time); powered at 5 VDC. Source: openQCM_Electrochemistry-Module-User_Manual, p.10 ### What does the openQCM Wi2 measure? *Applies to: Wi2* The openQCM Wi2 is a Quartz Crystal Microbalance that senses mass variations at the nanoscale by monitoring, in real time, the **frequency** variations of a piezoelectric quartz crystal sensor. Its measurement mode is **fundamental** frequency only, with a minimum sampling time of about 1 second. The integrated sensor module also reports temperature, but the physical quantity measured is frequency – the Wi2 does not measure dissipation. Source: openQCM_Wi2-user_manual.pdf, p.5, p.13 ### Which quartz crystal sensors are compatible with the Wi2? *Applies to: Wi2* The Wi2 uses a single quartz resonator sensor. The compatible and tested crystals are **5 MHz and 10 MHz** sensors with a **14 mm blank diameter** and **wrapped (single-sided) contacting** electrodes. The sensor module is designed for multi-quartz-dimension and multi-frequency housing compatibility. Source: openQCM_Wi2-user_manual.pdf, p.6, p.13 ### What are the QCM sensor and frequency specifications of the openQCM TWIN? *Applies to: TWIN* The mainboard supports **2 sensors** (a Sensor and a Reference) over a frequency range of **1 MHz to 25 MHz** . The measured physical quantity is frequency, and the measurement mode is **fundamental** . The control unit is a `Teensy 4.0` based on an ARM Cortex-M7, programmed in C++ (Arduino-based code). Source: openQCM_TWIN_User_Manual.pdf, p.9 ### What are the board dimensions, weight, and mounting requirements? *Applies to: TWIN* The openQCM TWIN board has a compact rectangular design measuring **59.8 x 53.5 x 19.6 mm** and weighs about **25 g** . The PCB material is Shengyi S1000-H (Tg 150) with a base thickness of 1.6 mm. It has four **2.2 mm** diameter mounting holes at the corners following a **56.4 x 49.5 mm** pattern, which accommodate **M2 screws** . A minimum clearance of **16.9 mm** from the mounting surface is required for components and connectors. Source: openQCM_TWIN_User_Manual.pdf, p.9, 21 ### What is the openQCM SpaceBug and what is it used for? *Applies to: SpaceBug* The **openQCM SpaceBug** is an ultra-compact, low-power Quartz Crystal Microbalance (QCM) module. It was originally designed for *aerospace research* — its miniaturized form factor suits space-constrained systems and small satellites such as CubeSats — and its low power and small size also suit other *battery-operated and power-constrained applications* . It acts as a core module to which users connect their own QCM peripherals, temperature sensors, and other I^2C-compatible devices, enabling a wide range of scientific experiments both in space and on the ground. Note: openQCM devices are released as scientific open-hardware instruments intended solely for scientific, research, development, demonstration, or evaluation purposes, and are not finished consumer end-products. Source: openQCM SpaceBug.pdf, p.3, 6 ### What are the physical dimensions and weight of the SpaceBug? *Applies to: SpaceBug* According to the dimensional schematic, the board measures **37.00 mm** in length and **26.00 mm** in width, with a thickness of **1.69 mm** . The technical specifications table lists the length as 37 mm, width as 30 mm, height as **< 8.5 mm** , and weight as **7 g** . The rectangular form factor is optimized for easy integration into space-constrained systems such as CubeSats. Source: openQCM SpaceBug.pdf, p.16, 17 ### What are the operating and storage temperature ranges? *Applies to: SpaceBug* The passive and integrated components were selected to operate at temperatures from **-40 °C to +80 °C** , which is also the rated working temperature. The storage temperature range is **-55 °C to +100 °C** . The safety section advises avoiding temperatures below -55 °C and above 100 °C, and never operating below -45 °C or above 80 °C. Using the device outside these ranges may alter materials and components and cause malfunction. Source: openQCM SpaceBug.pdf, p.8, 9, 17 ### Which QCM quartz sensors are compatible with the SpaceBug? *Applies to: SpaceBug* The SpaceBug supports a **single** AT-cut quartz resonator sensor with a frequency range from **1 MHz to 10 MHz** . It is specifically compatible with **5 MHz and 10 MHz** crystals, with a 14 mm blank diameter, wrapped with single-sided contacting. The QCM sensor is driven by a Pierce oscillator and measured at the fundamental frequency, with a typical sampling time of about **1 s** . Source: openQCM SpaceBug.pdf, p.11, 17 ### What quartz sensors and temperature range does the openQCM Holder support? *Applies to: Holder* The Holder accepts a single quartz resonator sensor with a fundamental frequency from **1 MHz to 10 MHz** and a **14 mm blank diameter** (single-sided contacting, wrapped). It uses a Pierce oscillator interface and measures frequency. Temperature is monitored by an I2C MCP9808-E/MS sensor (-40°C to +125°C), and the recommended working temperature is **15–45°C** . The board measures 40.2 mm long with the USB (25 mm without), 18.6 mm wide and 4 mm high, weighing less than 5 g. Source: openQCM Holder.pdf, p.8 ### What are the specifications of the openQCM AT5 and AT10 quartz crystals? *Applies to: all instruments* Both are AT-cut, plano-plano crystals with wrapped Ti/Au electrodes for single-side contact, optimised for liquid biosensing, and compatible with openQCM and Q-Sense instruments. | | AT5-14-12-AU-WRAP | AT10-14-12-AU-WRAP | | --- | --- | --- | | Nominal frequency | 5.000 MHz | 10.000 MHz | | Tolerance | ±7 kHz | ±5 kHz | | Q-value | > 100 000 | > 100 000 | | Shunt capacitance C0 | typ. 8 pF | typ. 8 pF | | Frequency vs temperature | < ±15 ppm (0–50 °C) | < ±15 ppm (0–50 °C) | | Blank diameter | 14.0 mm | 14.0 mm | | Front / back electrode | Ø 12.0 / 5.0 mm | Ø 12.0 / 5.0 mm | | Ti / Au thickness | 50 / 200 nm | not stated | | Overtones read by NEXT | up to 9th | up to 5th | For Sauerbrey calculations use an active area of 0.196 cm² (the Ø 5.0 mm back electrode). Source: AT5-14-12-AU-WRAP datasheet v1.1, p.3-4; AT10-14-12-AU-WRAP datasheet v1.0, p.4-5; openQCM NEXT user guide, p.9 ### What performance does every Q-1 have to meet before shipping? *Applies to: Q-1* The mounting manual defines a **factory acceptance test** , run with a 10 MHz AT-cut crystal at stable room temperature: at least 30 min in air, then 35 min in static deionised water. A unit passes when: | Parameter (fundamental) | Air | Static water | | --- | --- | --- | | Frequency standard deviation | — | ≤ 2.0 Hz | | Dissipation standard deviation | ≤ 0.2 × 10−6 | ≤ 0.5 × 10−6 | | O-ring sealing | OK | OK | | Typical equilibrium time | ~10 min | ~20 min | Ambient during the test: 20–30 °C; the typical values were obtained at 28.1 °C. These are pass limits under these conditions, not guaranteed performance in every setup. Flow, overtones and other media will differ. Source: openQCM_Q-1-mounting_manual, p.44-45 ### What performance does every Wi2 have to meet before shipping? *Applies to: Wi2* Each Wi2 passes a **factory acceptance test** with a 10 MHz AT-cut crystal: at least 30 min in air, then 35 min in static deionised water. | Parameter | Air | Static water | | --- | --- | --- | | Frequency standard deviation | ≤ 1.0 Hz | ≤ 1.5 Hz | | O-ring sealing | OK | OK | | Typical equilibration time | ~10 min | ~20 min | Ambient during the test: 20–30 °C. These are pass limits for a unit under these conditions, not a guarantee for every setup. The Wi2 measures frequency only, so there is no dissipation criterion. Source: openQCM_Wi2-mounting_manual, p.44-45 ### Is the Wi2 battery-powered or wireless? *Applies to: Wi2* Neither, as standard. The Wi2 is **powered at 5 VDC through USB** , and the same cable carries the data to the computer. There is no battery. It is **wireless-ready** : the design leaves room for an optional wireless module, and the validation procedure includes extra checks when one is fitted. Out of the box, plan on a USB connection to a PC. Use only a 5 VDC USB supply: a different power supply will damage the device. Source: openQCM_Wi2-user_manual, p.6, 13-14; openQCM_Wi2-mounting_manual, p.44 ### What power and room conditions does openQCM NEXT need? *Applies to: NEXT* - **Power** : two cables. The USB data cable goes to the computer and also powers the main electronics at 5 VDC. The USB TEC power cable runs from the supplied 5 V / 2.1 A adaptor to the `5VDC` jack and feeds the Peltier thermal control. Do not use other supplies. - **Room** : indoors, away from air-conditioning flows, direct sunlight, phones and motors. Do not operate it at ambient temperatures below 5 °C or above 30 °C. - **Storage and transport** : dry, between 0 and 50 °C. - **Cell temperature** : controllable from 25 to 45 °C. A 10k thermistor just below the crystal reads the cell temperature. Source: openQCM NEXT user guide, p.7-9, 11-12, 14 ### Are openQCM instruments finished, certified products? *Applies to: all instruments* No. openQCM devices are released as **scientific open-hardware instruments** . They are intended for research and development, demonstration and evaluation, and they are not finished end-products for general consumer use. The manuals note that the devices are outside the scope of the usual consumer-product compliance schemes (for example CE, FCC part 15, RoHS/WEEE). Electrostatic-discharge precautions and safe integration are the user’s responsibility. If you need to build an openQCM board into a regulated product, contact us to discuss what testing that would require. Source: openQCM NEXT user guide, p.1-8; openQCM_Wi2-user_manual, p.15; openQCM SpaceBug, p.3 ### Should I use 5 MHz or 10 MHz crystals? *Applies to: all instruments* Sauerbrey sensitivity scales with the square of the fundamental frequency: about 17.7 ng·cm⁻²·Hz⁻¹ at 5 MHz and 4.42 ng·cm⁻²·Hz⁻¹ at 10 MHz. Over the 0.196 cm² active area that is about 3.5 ng/Hz and 0.9 ng/Hz. A 10 MHz crystal therefore gives four times the shift for the same mass. - **10 MHz:** very small rigid mass changes, thin films, gas-phase adsorption. Thinner and more fragile, and it saturates at a smaller load. - **5 MHz:** heavier or thicker coatings, particles, viscous samples. More robust, and on the Q-1 and NEXT it gives more overtones: up to the 9th (five harmonics) against the 5th (three harmonics) at 10 MHz. The usual choice for multi-harmonic, viscoelastic work. Both have the same gold surface and fit all openQCM modules, so functionalisation protocols are identical. Select the matching frequency in the software when you calibrate. If unsure, test both with your sample. Source: openQCM support archive (41 threads) ### Should I buy liquid-biosensing crystals or standard crystals? *Applies to: all instruments* Both are AT-cut 14 mm blanks with gold electrodes and wrapped contacts. The difference is the electrode layout. - **Liquid-biosensing** (current AT5/AT10-14-12-AU-WRAP): a 12 mm front electrode over a 5 mm back electrode. The mass-sensitive region, set by the back electrode, stays well inside the wetted gold surface and away from the O-ring and the crystal edge. In liquid this reduces edge effects and gives a steadier, less noisy baseline, especially with viscous media and at higher overtones. - **Standard crystals** with smaller or equal electrodes work well in air, gas and vacuum, and can be used in liquid with somewhat more noise. If you work in both air and liquid, the biosensing type is the more versatile choice. Whatever the type, the contact side must face the spring contacts: a wrapped crystal cannot be turned over and used from the other side. Source: openQCM support archive (28 threads) ### What should I tell my lab safety officer about an openQCM instrument? *Applies to: all instruments* openQCM instruments are scientific open-hardware apparatus for research and development (see the FAQ on certification). For a safety review, the relevant points are: - **Electrical:** the electronics run at 5 V DC from USB, and the crystal is driven at very low RF power. The NEXT also uses a supplied 5 V adaptor for its thermal module. Use only the specified supplies. - **Liquids:** the main practical risk is leakage from a badly assembled cell or a pressurised line, which can also break the crystal. - **Chemicals:** check the wetted materials (crystal, FKM O-ring, PMMA or PTFE cell) against your samples. Solvents attack PMMA. - **Breakage:** the quartz crystal and the quartz cylinder of the EQCM cell are fragile. Wear gloves, and safety glasses when handling the cylinder. - **Environment:** indoor use only, not near flammable gases, fumes or liquids. Schematics can be provided on request for an institutional review. Source: openQCM support archive (2 threads) ### How high is the liquid layer in the measurement chamber, and how much of the crystal is wetted? *Applies to: Q-1, Wi2, NEXT* The standard chamber above the crystal holds about **50 µL** on the Q-1, Wi2 and NEXT. It is defined by the O-ring pressed on the crystal. The liquid layer is roughly 0.5 mm high, set by the part of the O-ring that protrudes from the cover; on the Q-1 and Wi2 it changes slightly with the lever position. The wetted area is the circle inside the O-ring, about 11 mm in diameter, so roughly 1 cm². It is the same for the flow cover and the open pipetting cover. The crystal edge and the back face, where the contacts are, stay dry. Do not confuse the wetted area with the Sauerbrey active area: for mass calculations use 0.196 cm², the Ø 5.0 mm back electrode of current crystals. The electrochemistry cells are much larger, about 15 mL. If your experiment needs a different liquid height, a custom cell with a modified O-ring seat is possible. Source: openQCM support archive (8 threads) ### What are the differences between openQCM Wi2, Q-1 and NEXT? *Applies to: Q-1, Wi2, NEXT* | | Wi2 | Q-1 | NEXT | | --- | --- | --- | --- | | Electronics | Pierce oscillator and counter | Scalar network analyser (sweep) | Scalar network analyser (sweep) | | Quantities | Frequency | Frequency and dissipation | Frequency and dissipation | | Harmonics | Fundamental | One per session (fundamental or one overtone) | All available overtones in every multiscan cycle, about 1.4 s per overtone (about 7 s for five overtones) | | Temperature | Monitored | Monitored | Active Peltier control, 25–45 °C | | Wetted cell | PMMA or PTFE, FKM O-ring | PMMA or PTFE, FKM O-ring | PTFE, FKM O-ring | | Electrochemistry | No | e-QCM module | e-QCM module | All three take one 14 mm wrapped 5 or 10 MHz crystal in a cell of about 50 µL. Choose the **Wi2** for frequency-only work: gas sensing, rigid films, deposition, teaching. Choose the **Q-1** when you need dissipation in liquid or with soft samples, where an oscillator may stop. Choose the **NEXT** for multi-harmonic viscoelastic analysis, temperature-controlled experiments, solvents, and its pipetting, optical and electrochemistry modules. A Wi2 cannot be upgraded to a Q-1, because the electronics are different. Source: openQCM support archive (62 threads) ### How should I cite openQCM in a publication? *Applies to: all instruments* Name the instrument model and give the website, for example: *The measurements were performed with an openQCM [model] quartz crystal microbalance (openQCM by Novaetech S.r.l., https://openqcm.com).* For reproducibility, also report: - the crystal type: fundamental frequency, electrode material and part number; - the harmonic or harmonics analysed; - the temperature conditions and, for the NEXT, the set point; - how mass was derived, for example the Sauerbrey equation with the active area used (0.196 cm² for current AT5/AT10 crystals); - for dissipation, that it is the openQCM instrumental value and the software version used. A list of peer-reviewed papers that used openQCM instruments is on the website and is a good source of methods for similar applications. Source: openQCM support archive (2 threads) ### Can I use crystals from other suppliers, or openQCM crystals in Q-Sense instruments? *Applies to: all instruments* openQCM modules accept AT-cut crystals with a **14 mm blank** and **wrapped electrodes** : the front electrode wraps around the edge, so the contacts of both electrodes are on the back, where the pogo pins or spring contacts sit. Electrode diameter, coating and surface finish are not critical, and Q-Sense-type sensors in this format work. Not compatible: - crystals with contacts on both faces, or keyhole designs without wrap-around; - deposition-monitor crystals whose two contacts belong to the same back electrode; - smaller blanks, or crystals in HC-type holders. Edge thickness profiles vary between makers, which changes how the O-ring presses. If a third-party crystal leaks or drifts, adjust the cover pressure. The Q-1 and NEXT software expect 5 or 10 MHz fundamentals. The other way round, the AT5/AT10 datasheets list Q-Sense compatibility, and 5 MHz openQCM crystals have been used in Q-Sense instruments. Those instruments are designed around 5 MHz, and users report less stable signals with 10 MHz. Start with one box and verify. Source: openQCM support archive (40 threads) ### My crystals resonate a few kHz away from the nominal frequency. Is that a problem? *Applies to: all instruments* Usually not. Every quartz blank is slightly different, and the datasheet tolerance is ±7 kHz for 5 MHz crystals and ±5 kHz for 10 MHz crystals. Crystals from the same wafer tend to cluster, while different batches can show a systematic offset. This is a normal result of the material and the lapping process. A QCM measurement uses the **frequency shift from each crystal's own baseline** , not the absolute frequency. The Sauerbrey sensitivity scales with f_0², so an offset of 5 kHz on a 10 MHz crystal changes it by about 0.1 %, which is negligible. Record a stable baseline for each crystal in the starting medium and use the software reference function to zero it. Some custom setups need a tight absolute frequency, for example an analog front-end with a narrow input range. In that case contact support: crystals can be measured individually and selected around a preferred centre frequency. Source: openQCM support archive (2 threads) ### Can I heat, bake or anneal a crystal? *Applies to: all instruments* Always remove the crystal from the instrument first. The sensor modules, O-rings, windows and electronics are rated far below typical annealing temperatures; the nylon parts, for example, are rated to about 80 °C. For the crystal itself, the AT5/AT10 datasheets specify frequency behaviour only over 0–50 °C and give no maximum treatment temperature. Bare quartz tolerates much more heat than the instruments, but the electrode stack (gold on titanium) and any coating can change when heated, so the resonance and the surface chemistry may not return exactly to their previous state. If your process needs a heat treatment, ask support first and test it on a spare crystal. After any thermal treatment, let the crystal cool fully, remount it, recalibrate, and compare frequencies only at the same temperature and in the same medium. Do not attribute the shift across the treatment to mass without this check. Source: openQCM support archive (7 threads) ### Can I put the instrument in an incubator, oven or humid chamber? *Applies to: Q-1, Wi2, NEXT* The complete instruments are designed for normal laboratory conditions. The manuals ask for indoor, dry operation at an ambient temperature between 5 and 30 °C, away from condensation and liquids. The nylon parts of the Q-1 and Wi2 are rated to about 80 °C, but that is a material limit, not an operating range for the electronics. - For a controlled cell temperature, use the NEXT, which regulates the measurement chamber between 25 and 45 °C while it sits in the lab. - For hot, humid or vacuum environments, put only the crystal, in a holder without electronics, in the harsh zone. Keep the electronics outside, connected by a short shielded cable or a feedthrough. - Whatever the setup, expect drift until the crystal reaches thermal equilibrium, and record a temperature–frequency calibration if the temperature changes during the run. For conditions outside these limits, contact support to discuss a custom setup. Source: openQCM support archive (10 threads) ### Can I use crystals with a fundamental other than 5 or 10 MHz, or measure at 100 MHz? *Applies to: Q-1, Wi2, NEXT* The Q-1 and NEXT are calibrated for 5 and 10 MHz crystals and sweep from about 1 to 50 MHz. That covers the 10 MHz fundamental up to the 5th overtone and the 5 MHz fundamental up to the 9th. - **Other fundamentals within the range,** for example 6 or 9 MHz: possible in principle, but the calibration and peak-search parameters in the open-source software must be adapted (see the FAQ on 6 MHz crystals). Contact support before ordering crystals. - **Around 1 MHz:** not advisable. A 1 MHz AT-cut crystal is about 1.7 mm thick and does not fit the cell, which is designed for thin 14 mm blanks. - **100 MHz:** out of range. The DDS synthesiser (AD9851) and the filters are designed for operation up to about 50 MHz. The Wi2 counter covers a wide band, but its oscillator and cell are designed for 5 and 10 MHz crystals. Non-standard crystals are custom productions with minimum order quantities. Source: openQCM support archive (5 threads) ### Can I make data acquisition faster than the standard sampling time? *Applies to: Q-1, Wi2, NEXT* The limit comes from how each instrument measures. - **Q-1 and NEXT** rebuild each resonance with a frequency sweep. The Q-1 follows one harmonic at about 1.0 s per point. The NEXT reads all available overtones in every multiscan cycle (about 1.4 s per overtone, so about 7 s for five overtones), which is also the minimum datalog interval. The sweep code is open source and can be changed, but sweeping too fast distorts the resonance curve because the crystal needs time to respond, so frequency and dissipation become noisier and less accurate. Validate any change against a known reference such as an air-to-water step. - **Wi2 and other oscillator devices** count cycles over a 1 s gate. A shorter gate in the open firmware gives proportionally coarser steps: a 100 ms gate gives about 10 Hz steps instead of about 1 Hz. Sweep-based QCM is not suited to millisecond kinetics. For most adsorption, binding and film-growth processes, sampling every one to a few seconds is enough, and a longer logging interval gives smoother data. Source: openQCM support archive (19 threads) ### Is there a multichannel openQCM? *Applies to: all instruments* There is no standard multichannel instrument. The practical options are: - **Several instruments in parallel** , each connected to the PC by USB, identified by its own COM port and running its own software instance. This works well for a reference and a sample channel, but the channels are not strictly synchronised. - **openQCM TWIN** , an OEM board with a sensing and a reference oscillator channel for differential frequency measurements, designed for gas and vacuum applications. - **Custom oscillator arrays** built on request: one board coordinating several channels that measure the fundamental frequency only. Multichannel frequency and dissipation is beyond the current sweep-based platform, where one synthesiser and one detector serve one crystal. It would require a redesign of the electronics. Contact support to discuss custom configurations. Source: openQCM support archive (7 threads) ### One overtone on my NEXT is much noisier than the others. Is that normal? *Applies to: NEXT* Some difference is normal. The highest overtones sit close to the upper frequency limit of the electronics, around 50 MHz, and their resonance peaks are smaller. Their dissipation in particular is noisier, especially in liquid. With 5 MHz crystals the 3rd, 5th and 7th overtones usually give the most reliable data, and the 9th is best used as a cross-check. Suspect a fault when: - one overtone stays noisy across several crystals and coatings while its neighbours are stable, or - the noise appeared suddenly on an instrument that used to be quiet. First rule out the usual causes: bubbles, a fluidic module that is not fully seated, a worn or contaminated crystal, and electromagnetic interference from nearby equipment. If the problem persists, send support a screenshot of the sweep signals from the Raw data view with a short description. Later production units include hardware improvements to shielding, signal traces and module contacts. Source: openQCM support archive (3 threads) ### What comes with a Q-1 or Wi2, and what else do I need to order? *Applies to: Q-1, Wi2, NEXT* The **Q-1** and **Wi2** ship with the control unit, the sensor module with its top fluidic cover, a test crystal already mounted (usually 10 MHz), a USB cable and spare O-rings. Each unit is tested in air and in water before shipping and comes with a test report. The NEXT package is described in its own FAQ. Plan to order or provide separately: - a box of crystals, since crystals are consumables; - tubing and a pump for flow work: a peristaltic pump in pump-out mode or a syringe pump. For static work a syringe or pipette is enough; - a PTFE cover if you will use solvents, and optional covers or modules such as the open pipetting cover or the electrochemistry module; - a computer running Windows, macOS or Linux. Software and manuals are not shipped on media. Download them free from the product pages on openqcm.com. Source: openQCM support archive (27 threads) ### Why can the NEXT not go above 45 °C, and what limits it at the low end? *Applies to: NEXT* The NEXT regulates the measurement chamber from **25 to 45 °C** with a Peltier element, a Thorlabs MTD415T controller and a 10 kΩ thermistor just below the crystal. - **Upper limit:** 45 °C is a hardware limit of the controller and thermistor, not a software setting, so it cannot be raised in the software or by warming the room. For 50–60 °C or more you need external heating of fluid and sample, or a custom design with a different controller. - **Lower end:** the Peltier must pump heat into the heat sink and the room, so performance near the bottom of the range depends on the lab temperature and on the heat sink. Keep the lab cool, do not ramp down too fast, and make sure the heat sink is not already hot. For good control, the fluidic module must be fully seated on the Peltier, with no grease. Liquid is brought to temperature in channels machined into the PTFE core, but inlet tubing and external reservoirs are not heated, so allow time to equilibrate. Source: openQCM support archive (33 threads) ### What does open source mean for openQCM in practice? *Applies to: all instruments* The firmware, software and mechanical designs are shared openly, and researchers may study and modify them. Source code comes with the software downloads, and schematics, pinouts and 3D files of parts such as covers are available on request. Documentation is released under the CC BY-NC-SA 4.0 licence. In practice you can: - read exactly how frequency and dissipation are computed; - change sweep windows, logging or output formats in the software; - adapt holders or covers to your setup; - integrate the instruments into your own acquisition system. The lower price reflects this model: there are no proprietary licences, and development is driven by feedback from the user community. Every instrument is still assembled and tested as a scientific instrument before shipping, and is intended for research, development and demonstration use. Source: openQCM support archive (6 threads) ## Hardware, sensors & assembly ### What oscillator circuit does openQCM use, and how do I estimate the drive level? *Applies to: all instruments* Wi2, TWIN, SpaceBug and the original openQCM use a quartz-crystal oscillator in **Pierce configuration** (SN74LVC1GX04 on current boards) whose output the microcontroller counts; Q-1 and NEXT have no oscillator and sweep the crystal passively. The drive level relates to the crystal’s motional resistance and therefore to the damping of the resonator. Oscillators can include an **Automatic Gain Control (AGC)** that keeps the signal level constant by adjusting the amplifier gain — measuring the AGC voltage gives you the level applied to the sensor. The openQCM Pierce boards have no AGC. For background, see Arnau’s review, [“A Review of Interface Electronic Systems for AT-cut QCM Applications in Liquids”](http://www.mdpi.com/1424-8220/8/1/370/htm). Source: https://forum.openqcm.com/d/10-driver-lever-for-qcm-sensor ### How do I calibrate the Pierce oscillator for a different crystal frequency? *Applies to: all instruments* The shield is optimised for 10 MHz: after a calibration campaign we settled on **100 pF** for C1/C2 (the first version used 33 pF). Although the oscillator can drive from a few kHz up to ~28 MHz, using a markedly different resonance frequency means you should **change C1, C2 and possibly R3** to keep a good signal across your conditions. Source: https://forum.openqcm.com/d/12-calibration-for-pierce-oscillator-ciruit-in-openqcm ### Where can I buy spare pogo pins? *Applies to: all instruments* You can source them from Mouser, part number [581-709150001050006](https://www.mouser.com/ProductDetail/581-709150001050006). Source: https://forum.openqcm.com/d/32-pogo-pins ### Can the sensor holder accept a different electrode shape? Can I get the CAD model? *Applies to: all instruments* Yes. For electrodes on opposite faces of the crystal you can reposition the pogo-pin contacts; the sensor will sit slightly tilted but works perfectly well. The pogo-pin spacing can be changed by editing the design. We can share the **CAD files of the sensor holder / sensor module** on request — just [contact us](https://openqcm.com/contacts/). Source: https://forum.openqcm.com/d/43-cad-model-for-sensor-holder ### My cell-module temperature reads 0 °C (and frequency may read 0 Hz). What happened? *Applies to: all instruments* This is typically caused by **liquid that has entered and settled on the sensor-head PCB** inside the cell module. To recover it: 1. Disassemble the cell module — remove the quartz crystal and lid, then the rubber feet to expose the screws. 2. Carefully remove the two O-ring screws (mind the washers) and lift out the PCB. You can ease it past the USB port to free the blue LED from its groove. 3. Clean the PCB in an **ultrasonic bath with isopropyl alcohol for ~5 minutes** (LED and USB can be submerged). 4. Let it dry completely, test the bare PCB, then reassemble in reverse order. Source: https://forum.openqcm.com/d/22-cell-module-temperature-sensor ### Can I use the sensor without the lid, or wire an external sensor head? *Applies to: all instruments* Yes. You can run the sensor without a lid — you will only see **more noise** because the crystal is exposed to the environment. You can also wire your own sensor head to the main electronics; keep the leads **as short as possible** and shield the connection to ground. Source: https://forum.openqcm.com/d/27-use-open-qcm-wi2-without-lid ### I get no peak, or 0 Hz with the crystal installed (but resonance without it). What should I check? *Applies to: all instruments* First make sure the quartz is **mounted and connected correctly** and that the pogo-pin contacts are seated. Check whether you are using **wrapped vs. non-wrapped electrodes** , as this affects contact. If the peak is simply outside the search window, widen the sweep range in the software (see the Software section). Source: https://forum.openqcm.com/d/33-no-peak ### My frequency drifts continuously. How do I stabilise it? *Applies to: all instruments* Continuous drift often comes from **O-ring swelling** and from **mechanical stress at the pogo-pin contacts** . Two remedies: (1) gently **tap the fluidic cell** to release O-ring stress; (2) fine-tune the pogo-pin height using the **1.3 mm hex hole on the bottom of the sensor module** (a 1.3 mm hex key). If drift persists after this, get in touch. Source: https://forum.openqcm.com/d/25-continuous-increase-in-frequency ### Where exactly does the temperature sensor measure, and what is its operating range? *Applies to: all instruments* The I²C temperature sensor is embedded in the openQCM shield, between the microcontroller and the quartz crystal, so it reports the temperature *inside* the device close to the sensor. The Arduino board and the openQCM shield should be operated within **−40 °C to +85 °C** . ### How do I connect openQCM NEXT to power and to my computer? *Applies to: NEXT* openQCM NEXT requires both supplied cables. Connect them in this order: 1. Plug the **USB TEC power cable** into the `USB XP` power adapter, and its female jack into the openQCM NEXT `5VDC` socket. 2. Connect the `USB XP` power adapter to the mains. 3. Connect the **USB data cable** to your PC. Use the device indoors in a lab, away from air-conditioning flows, direct sunlight, and electromagnetic sources such as smartphones and motors, which can affect measurement quality. Source: openQCM NEXT user guide, p.12 ### What comes in the openQCM NEXT package? *Applies to: NEXT* The package contains everything needed to start measuring: - 1 openQCM NEXT main module - 1 fluidic module - 1 × 5 MHz Ti/Au quartz sensor (for testing) - 1 USB data cable - 1 USB TEC power cable - 1 USB XP Power adaptor (5 V cc, 2.1 A) Source: openQCM NEXT user guide, p.11 ### How do I mount the quartz sensor in the correct orientation? *Applies to: NEXT* openQCM sensors use wrapped contact electrodes, so the electrical contacts are only on one side. Place the sensor with its **bottom-side contacts** aligned to the gold spring contacts of the fluidic module base, following the orientation shown in the manual. Correct alignment of the spring contacts with the quartz electrodes is essential, as incorrect alignment results in improper sensor operation. After verifying the position, close the top cover and tighten the two slotted round nuts. Source: openQCM NEXT user guide, p.15-16 ### How do I insert and remove the fluidic module? *Applies to: NEXT* To **insert** : place the fluidic module into the white PTFE slot on the heat sink, fitting its side pins into the corresponding holes, then gently slide it upwards until it reaches the ledge and you hear the characteristic click (on versions from 2023 onward). This ensures correct electrical contact with the main electronics. To **remove** : press the metal clip using the included tool or another plastic accessory, and while keeping the clip pressed, slide the fluidic module downwards. Source: openQCM NEXT user guide, p.17 ### What is the pipetting module and how do I set it up? *Applies to: NEXT* The pipetting module is an optional PTFE accessory for static, controlled sample release directly onto the sensor (suitable for evaporation studies and external chemical reactions). Insert the PTFE "pipetting core" into its aluminium shell so that its central hole is concentric with the hole on the shell; if it does not line up, remove it, rotate it, and reinsert. Mount the sensor and close the cover as usual. Because pipetting is done with the module horizontal, slightly loosen the two side screws on the heatsink to tilt it — **do not unscrew them completely** , or the device body may disassemble. A small lid is provided to protect the sample from contamination and evaporation. Source: openQCM NEXT user guide, p.18 ### What is the optical module and what window does it use? *Applies to: NEXT* The optional optical module is a fluidic module with a housing for an optical window, used for visual inspection or parallel optical measurements such as spectroscopy or Raman. By default it is fitted with a 9 mm diameter quartz window 3 mm thick, but you can mount a custom window of the same size. The window is held in the Teflon element by a mechanical joint (no adhesives, to avoid contamination). Because of the mechanical discontinuity, this module is more prone to trapping air bubbles, so visually check that no bubbles are present in the measuring cell before measuring. Source: openQCM NEXT user guide, p.19 ### How do I check which side of the QCM sensor faces the pogo pins? *Applies to: Q-1* openQCM uses quartz sensors with **wrapped contact electrodes** , meaning the electrical contacts are on a single side. The sensing side (top) carries the larger gold electrode and must face the sample, while the bottom side carries the smaller electrode pattern that interfaces with the pogo pins. Always verify the correct orientation before mounting so that the contact is made on the proper (single-sided) face. Source: openQCM_Q-1-user_manual, p.9 ### How do I mount a quartz crystal in the Q-1 sensor module? *Applies to: Q-1* Follow these steps to house the sensor correctly: 1. Remove the top fluidic cover. 2. Place the quartz crystal into the sensor module housing, making sure the electrodes on the back surface are in contact and aligned with the pogo pins. 3. Insert the top fluidic cover. The fine-tuning lever must be set to **min** , otherwise the cover will not slot in. 4. Turn the lever counterclockwise to ensure sealing of the sensor module. Source: openQCM_Q-1-user_manual, p.10 ### How can I verify that the Q-1 sensor module is correctly sealed? *Applies to: Q-1* Run a simple aspiration test on the fluidic chamber: 1. Connect one tube from the cover inlet to a water reservoir. 2. Connect a second tube from the cover outlet to a syringe. 3. Aspirate liquid with the syringe and stop before the liquid enters the quartz chamber. If the liquid level remains stationary, the seal is good. If not, finely turn the lever counterclockwise toward **MAX** to improve sealing. Be careful: turning the lever clockwise can cause the cell to lose its seal and flood. Source: openQCM_Q-1-user_manual, p.11 ### How does the Wi2 measure frequency, and what is its frequency range? *Applies to: Wi2* The Wi2 electronics are built around a quartz crystal oscillator in **Pierce configuration** , using the `SN74LVC1GX04` inverter to create a crystal oscillator with a buffered square-wave output. Frequency is read by a **Teensy 3.2** microcontroller (32-bit ARM) using the `FreqCount` library, which counts pulses over a fixed gate interval (typically 1 second) via the hardware timer. The Teensy 3.2 can measure frequency from **1 kHz up to 65 MHz** (nominally). Source: openQCM_Wi2-user_manual.pdf, p.5 ### How do I know which side of the quartz sensor faces the pogo-pins? *Applies to: Wi2* openQCM quartz sensors use **wrapped contact electrodes** (single-side contact), so the orientation matters. The **top side is the sensing side** , and the **bottom side** – where the wrapped electrode contacts are located – must face the **pogo-pins** . Always verify the correct side before placing the crystal into the housing. Source: openQCM_Wi2-user_manual.pdf, p.7 ### How do I mount a quartz crystal in the Wi2 sensor module? *Applies to: Wi2* Follow these preliminary steps for correct sensor housing: 1. Remove the top fluidic cover. 2. Place the quartz crystal into the sensor module housing, making sure the electrodes on the back of the sensor are in contact and aligned with the pogo-pins. 3. Insert the top fluidic cover – the fine-tuning lever must be positioned on **min** , otherwise the cover will not fit into its slots. 4. Turn the lever **counterclockwise** to ensure the sealing of the sensor module. Source: openQCM_Wi2-user_manual.pdf, p.8 ### What is the openQCM TWIN and how does it differ from a single-crystal QCM? *Applies to: TWIN* The openQCM TWIN is a **dual-crystal Quartz Crystal Microbalance** system that uses a differential measurement approach with a reference-sensor crystal configuration, designed specifically for gas and vacuum applications. It drives two quartz crystals with two precision oscillator circuits: one crystal is the sensing element exposed to the measurement environment, and the other is a reference crystal operating under identical conditions. Compared to single-crystal open-source QCM systems, this dual architecture enables *real-time compensation of environmental factors* , particularly temperature-induced frequency shifts. It is supplied as an OEM platform intended to be integrated with custom sensor holders. Source: openQCM_TWIN_User_Manual.pdf, p.10 ### What accessories are included with the openQCM TWIN mainboard? *Applies to: TWIN* The kit includes the following items: - 1 openQCM TWIN mainboard with pre-installed Teensy 4.0 sockets - 1 Teensy 4.0 with pre-installed sample firmware - 1 USB data cable - 1 USB TEC power cable - 1 USB XP Power adaptor, 5V DC, 2.1 A - 5 Male SMA to Male MMCX cables, 200 mm, terminated 50 Ω - 1 Sample Peltier thermistor kit Source: openQCM_TWIN_User_Manual.pdf, p.8 ### How should I power the openQCM TWIN and what are the voltage limits? *Applies to: TWIN* The main electronics are powered with **5 VDC through the USB port** , with a maximum current of **1.6 A** . The board uses two power inputs: a micro-USB connector that supplies power and data communication to the control board (via the Teensy 4.0), and a dedicated **5V DC power jack (1.05 x 3.5 mm)** dimensioned for the higher current requirements of the TEC module. The TEC controller supply input is rated **4.5 V to 6 V** at up to **1.6 A** . Using a power supply other than the one indicated will damage the device. Source: openQCM_TWIN_User_Manual.pdf, p.6, 9, 16, 19 ### What temperature range can the openQCM TWIN safely operate in? *Applies to: TWIN* TWIN is a bare board with no case; the manual recommends operation between **0°C and 50°C** . The passive and integrated electronic components are rated for the commercial range, so electronics operation is recommended within **0°C to 70°C** . Using the device outside these limits can alter materials and components and cause malfunction. Source: openQCM_TWIN_User_Manual.pdf, p.6 ### How are the two crystal oscillator channels designed? *Applies to: TWIN* The frequency measurement section uses **two identical Pierce oscillators** , each built around a `SN74LVC1GX04` IC (IC1, IC2) from Texas Instruments, optimized for crystal oscillator applications and operating from 1.65 V to 5.5 V. One oscillator drives the sensing crystal exposed to the environment, while the other drives the reference crystal under identical conditions. Each circuit uses matched components: a **2.2 MΩ** feedback resistor (R8, R10), a **1 kΩ** current-limiting resistor (R9, R11), and **100 pF** load capacitors (C8, C9 for sensor; C11, C12 for reference). Each oscillator has ground-plane isolation and uses RF connectors to ensure frequency stability. Source: openQCM_TWIN_User_Manual.pdf, p.12 ### What connectors are on the board and how do I wire the TEC and crystal signals? *Applies to: TWIN* The board groups connectors by function: - **Temperature control:** `10k thermistor L` and `10k thermistor R` for two 10 kΩ NTC thermistors, plus `TEC-` and `TEC+` power connections. - **Frequency measurement:** `SENS IN`/`SENS OUT` for the sensor crystal, `REF IN`/`REF OUT` for the reference crystal, and `TTL FREQ DIFFERENCE` for the differential output. - **Fan:** `FAN GND`, `FAN VDC`, `FAN RPM`, `FAN PWM`. - **Power:** `5 VDC PWR TEC` and the micro-`USB` connector. Note the TEC polarity: connect `TEC-` to the TEC positive terminal and `TEC+` to the TEC negative terminal. Always observe correct TEC polarity, use shielded cables for frequency connections, and ensure good thermal contact for the thermistors. Source: openQCM_TWIN_User_Manual.pdf, p.18, 19 ### How does temperature control work on the openQCM TWIN? *Applies to: TWIN* Thermal control is built around the Thorlabs `MTD415T` temperature controller IC (U1), a compact module (21.0 x 12.4 mm) that delivers TEC currents up to **±1.5 A at 4.0 V** compliance voltage for both heating and cooling. It uses a **10 kΩ NTC thermistor** and provides a measurement resolution better than 10 mK (typically 2 mK) over a control range of **+5°C to +45°C** , with typical temperature stability of 100 mK via a digital PID loop. The TEC power input is protected by a resettable PPTC fuse rated at **2 A** , and the controller adds overtemperature, open-circuit, and reverse-polarity protection. Source: openQCM_TWIN_User_Manual.pdf, p.13, 14 ### How do I power the SpaceBug and what is its power consumption? *Applies to: SpaceBug* The main electronics are designed to be powered with a **maximum of 5 VDC** ; the minimum operating voltage is **3V3** . Using a power supply other than indicated will damage the device. Power is supplied through the `VIN` pin; note that supplying 5 V to `VIN` will not back-power the USB port because a protection diode blocks it (peak draw 1 A, recommended < 500 mA). - Max current at 10 MHz: **50 mA** - Max current at 5 MHz: **40 mA** - Peak current at startup: **75 mA** - Deep Sleep Mode (after removing the power LED): **28.5 µA** Source: openQCM SpaceBug.pdf, p.8, 13, 17 ### What is included in the package? *Applies to: SpaceBug* The package contains everything needed to start taking measurements: - 1 × openQCM SpaceBug - 1 × compatible 3 V button battery - 1 × 10 MHz Ti/Au quartz sensor (for testing) - 1 × USB data cable Source: openQCM SpaceBug.pdf, p.15 ### What do the castellated connector pins do? *Applies to: SpaceBug* The castellated connectors are arranged for modular integration. Key pins include: - `VIN` – power input; `GND` – common ground for power and logic. - **I^2C** – four pins (`SDA`, `SCL`, `3V3`, `GND`) for interfacing temperature or other compatible sensors. - `TX`/`RX` – serial UART for telemetry and command; the `RX` line is shared with the RTC `_INT` pin to wake the SAMD21 from deep sleep (a Schottky diode prevents unwanted feedback). - `QCM_IN`/`QCM_OUT` – input/output of the Pierce oscillator for the quartz sensor. - `T+`/`T-` – the two ends of the temperature sensor in a voltage-divider network. Source: openQCM SpaceBug.pdf, p.13, 14 ### How do I connect and configure a temperature sensor? *Applies to: SpaceBug* The SpaceBug has a dedicated connector for a temperature sensor wired into a voltage-divider network using the `T+` and `T-` pins; the voltage across the sensor varies with temperature. It supports **10K NTC thermistors** and **PT100/PT1000 RTDs** . Depending on the sensor chosen (PT100, PT1000, or thermistor), you must mount the *appropriate matching resistor* in the voltage-divider network to ensure accurate measurements. Alternatively, an I^2C temperature sensor can be used via the dedicated I^2C pins. Source: openQCM SpaceBug.pdf, p.6, 11, 14 ### Can I add more sensors to the SpaceBug? *Applies to: SpaceBug* Yes. The SpaceBug offers expandability through its **4-pin I^2C connector** , letting you attach additional sensors and peripherals that communicate over the I^2C protocol. This enables complementary measurements such as humidity, pressure, or gas sensing alongside the QCM data, giving a more complete picture of the experimental conditions. The 4-pin QCM/temperature connector can also accept a custom sensor head or a stackable socket for different sensor configurations. Source: openQCM SpaceBug.pdf, p.6, 11, 14 ### How is measurement data stored on the device? *Applies to: SpaceBug* The SpaceBug includes an onboard **micro-SD card slot** for data storage, communicating with the SAMD21 microcontroller via the **SPI** protocol (`MOSI`, `MISO`, `SCK`, and `CS` pins). This lets researchers record experimental data directly on the device, ensuring valuable data is securely stored and accessible even if communication with the host system is lost. In the sample firmware, the SD chip-select is set to pin 2 and each record is logged as timestamp, temperature, and QCM frequency. Source: openQCM SpaceBug.pdf, p.6, 11, 22 ### What is the openQCM Quartz Holder? *Applies to: Holder* The openQCM Quartz Holder is a highly miniaturized Quartz Crystal Microbalance (QCM) device that integrates the structure and electronics into a single system built entirely from **FR-4 PCB** material. It uses just three FR4 PCB layers that serve as both the electronic substrate and the structural framework, eliminating the need for a plastic housing. This makes the Holder compact and inherently **vacuum-compatible** , so it is suitable for both atmospheric and high-vacuum applications. It hosts a single quartz resonator sensor and turns mass changes into shifts of the oscillation frequency, read by your own electronics. Source: openQCM Holder.pdf, p.9 (and p.8) ### How do I connect the openQCM Holder? *Applies to: Holder* The Holder can be connected in two ways: via its **USB connector** to custom reading/acquisition electronics, or by **soldering wires to its gold pads** . The gold-pad method is particularly suited to vacuum chambers where you need a connection through an electrical feedthrough. Refer to the documented footprint and pinout for the connection method you choose. Source: openQCM Holder.pdf, p.10-11 ### What temperature and voltage limits must I respect with openQCM devices? *Applies to: Holder* The Holder has no plastic case; operate the device only between **0°C and 50°C** . The electronic board's components are rated for the commercial range, so operation is recommended within **0°C to 70°C** . The electronics are powered with **3.3–5 VDC** (V+ pin), at a maximum current of **80 mA at 5 V** . Using temperatures or a power supply other than those indicated may alter the materials and components and damage the device. Source: openQCM Holder.pdf, p.6 ### Why are the two electrodes of the crystal different sizes? *Applies to: all instruments* The asymmetric layout is designed for work in liquid. The large Ø 12 mm electrode faces the sample, and the small Ø 5 mm electrode is on the back. The larger sensing electrode reduces **edge effects** , where field fringing at the electrode border causes unwanted frequency shifts. This keeps the active area well defined, and the mass response comes mainly from the centre of the crystal. Both electrodes are wrapped around the edge, so all electrical contacts are on the back. The back can therefore stay dry while the front is immersed. In practice: large electrode up, toward the sample (in an EQCM cell it is the working electrode), and contact pads down onto the pogo pins or spring contacts. Source: openQCM_NEXT-Electrochemistry-Module, p.16; openQCM NEXT user guide, p.15; AT5/AT10 datasheets, p.3-4 ### Can I use 1-inch crystals in the Q-1 or Wi2 sensor module? *Applies to: Q-1, Wi2* Physically, yes. The module has a large O-ring seat (ID 22 mm, cross-section 1.5 mm) designed to hold 1-inch sensors. The manuals still recommend the standard **14 mm** crystals for best performance: the 1-inch option exists, but it is not the recommended or validated configuration. If you try it, check the seal with the syringe test and watch the baseline for drift before you start an experiment. Source: openQCM_Q-1-mounting_manual, p.23, 28; openQCM_Wi2-mounting_manual, p.23, 28 ### Which temperature sensor do the Q-1 and Wi2 use, and where is it? *Applies to: Q-1, Wi2* Both use a **Microchip MCP9808** digital I²C sensor, accurate to **±0.25 °C** (typical). It sits on the small proximity board inside the sensor module, next to the pogo pins, as close as possible to the crystal. A small magnet keeps it in good mechanical contact with the crystal, so it reads the temperature inside the fluidic cell rather than the room temperature. The temperature is logged with every data point, which lets you correct frequency for temperature afterwards. Neither instrument has active temperature control. If you need a controlled cell temperature, use openQCM NEXT. Source: openQCM_Q-1-mounting_manual, p.16-18, 31; openQCM_Wi2-mounting_manual, p.8, 17, 31; openQCM_Q-1-user_manual, p.5 ### What should I watch for when reassembling the Q-1 or Wi2 sensor module? *Applies to: Q-1, Wi2* - **O-ring compression** : too much stresses the crystal and shows up as baseline drift; too little lets liquid leak and reach the electronics. Use only a thin film of O-ring grease. - **Window set screws** : tighten gently, because the PMMA window can crack. - **Plastic threads** : use a hand screwdriver, tighten diagonally and do not overtighten. - **Magnets** : check polarity before seating them. - **Crystal** : handle with clean tweezers or gloves, contact side toward the pogo pins. - **Internal USB-shaped connectors** : the sensor-module and main-unit connectors carry internal signals. Never plug them into a computer. After any reassembly, run a leak test and a baseline test before measuring. Source: openQCM_Q-1-mounting_manual, p.20, 28-40; openQCM_Wi2-mounting_manual, p.28-40 ### Does the SpaceBug coin cell power the measurements? How do I budget power? *Applies to: SpaceBug* No. The 3 V button cell in the box backs up the RV-3028 real-time clock, which draws about 45 nA. The board itself needs 3.3–5 V on `VIN`, or USB. | State | Current | | --- | --- | | Measuring, 10 MHz crystal | ≤ 50 mA | | Measuring, 5 MHz crystal | ≤ 40 mA | | Start-up peak | 75 mA | | Deep sleep (power LED removed) | 28.5 µA | Both 3.3 V regulators can be switched off from one GPIO. The RTC alarm wakes the board through `RX`, which is shared with the UART. Example (our estimate, not a manufacturer figure): one reading every 5 min, awake ~3 s at 50 mA, averages ~0.5 mA, roughly 80 days per 1000 mAh. Source: openQCM SpaceBug, p.10, 13, 15, 17, 25, 28 ### How do I wire the Holder gold pads, and how do they differ from the USB connector? *Applies to: Holder* The Holder’s connector has a USB 3.0 shape but a different pinout. **Never plug it into a computer.** For a vacuum feedthrough, solder to the gold pads instead: | Pin | USB-shaped connector | Gold pads | | --- | --- | --- | | 1 | SDA | GND | | 2 | QCM OUT | QCM IN (SENS−) | | 3 | QCM IN | SCL | | 4 | NC | SIG OUTPUT | | 5 | SIG OUTPUT | SDA | | 6 | GND | QCM OUT (SENS+) | | 7 | V+ | V+ | | 8 / 9 | GND / SCL | — | QCM IN and QCM OUT are in a different order on the two interfaces, so check before soldering. Supply 3.3–5 V (max 80 mA at 5 V). No outgassing or bake-out data are published yet, so ask us before high-vacuum use. Source: openQCM Holder, p.7-10 ### Why do the plastic parts of the instrument have a rough surface? *Applies to: all instruments* The plastic parts of openQCM instruments are made by **selective laser sintering (SLS) of PA2200 nylon** , a form of 3D printing, not by injection moulding. The process leaves a slightly rough, matte surface, but the parts are mechanically durable. Additive manufacturing keeps the instruments affordable and lets researchers modify or reprint parts for their own setups. The parts that touch the sample, such as the PMMA or PTFE windows, the PTFE cores and the O-rings, are made separately and are not affected by this texture. Clean the external parts with a damp cloth. The nylon case is heat-resistant only up to about 80 °C, so keep it away from ovens and hot plates. Source: openQCM support archive (1 thread) ### Which covers and modules exist, and can I swap them between Q-1, Wi2 and NEXT? *Applies to: NEXT, Q-1, Wi2* The Q-1 and Wi2 share one sensor-module family; the NEXT has its own. Parts do not cross between the two families. - **Q-1 and Wi2** : fluidic cover with PMMA window (standard, aqueous samples, visual inspection), fluidic cover with PTFE window (solvents, aggressive chemicals), PTFE open cover for pipetting, and the electrochemistry module, all on the same mounting interface. The current sensor module fits all Q-1 units. - **NEXT** : fluidic module (closed cell of about 50 µL, PTFE core), pipetting module (open well, used horizontal), optical module (quartz window) and electrochemistry module. They click into the same slot on the heat sink, so you can add modules later. When ordering, check that each accessory is listed for your instrument. Never plug a sensor module into a computer USB port: it connects only to its main unit. Source: openQCM support archive (11 threads) ### Can I start with a Wi2 and upgrade to dissipation monitoring later? *Applies to: Wi2, Q-1* Yes. The Wi2 and the Q-1 use the same sensor module, the fluidic cell with crystal contacts and temperature sensor that plugs into the main unit. To add dissipation, replace the Wi2 main unit (Pierce oscillator, frequency only) with a Q-1 main unit (network analyser, frequency and dissipation on the fundamental or a selected overtone). Your sensor module, covers, crystals and fluidic accessories stay the same. Contact openQCM to arrange the change. Whether you need dissipation depends on the application. Frequency alone is enough for rigid films, gas-phase sorption and thickness monitoring. In liquid, and with soft or hydrated layers such as proteins, cells or polymers, dissipation tells you whether a frequency shift reflects mass or viscoelastic changes. The NEXT uses its own modules, which are not interchangeable with the Q-1/Wi2 sensor module. Source: openQCM support archive (4 threads) ### Do I need an anti-vibration table, and does the sensor have to be horizontal? *Applies to: all instruments* **No anti-vibration table is needed.** The crystal resonates at megahertz frequencies, while building vibrations and footsteps are in the hertz to kilohertz range, so a normal bench is enough. Avoid knocking the cell during a run. Electromagnetic sources such as motors, pumps and phones matter more; keep them away. **Orientation** : the QCM works on piezoelectricity, not gravity, so any orientation is possible. A vertical cell keeps sedimenting particles off the sensor; a tilted cell helps bubbles leave through the outlet. - On the NEXT, loosen the two side screws of the heat sink slightly to tilt it, without removing them. The pipetting and electrochemistry modules must be horizontal. - A flat cable links the NEXT sensor head to the electronics. Choose one working orientation rather than tilting back and forth many times. If amplitudes or overtones change with the angle, contact support. Open liquid surfaces are the exception: they pick up small vibrations as baseline noise. Source: openQCM support archive (14 threads) ### Can I buy only the electronics boards and build my own QCM? *Applies to: Q-1, Wi2, Holder* Yes. The electronics are open hardware and are available without the case. There are two combinations: - **Frequency only** : Teensy shield (the Pierce oscillator of the Wi2) with a Teensy microcontroller and a 14 mm Quartz Holder *without* integrated oscillator. It gives about one frequency reading per second and runs with the Wi2 software. It suits gas-phase work, vacuum, thickness monitoring and proof-of-concept tests. - **Frequency and dissipation** : Q-1 shield (network analyser) with a Teensy and a passive holder, a sensor module, or your own resonator on SMA connectors. It works like a Q-1, one harmonic at a time, with the Q-1 software, and tolerates heavier loads and full immersion. The firmware is open source, so you can adapt it. Check the product page for the microcontroller generation and whether it is supplied pre-programmed. Keep the wiring between holder and board short and shielded. Source: openQCM support archive (43 threads) ### Which Teensy do the current shields use, and will my older board still work? *Applies to: Q-1, Wi2, Holder* Current Q-1 and Wi2 builds, the Teensy shield and the Q-1 shield are designed for the **Teensy 4.0** . The firmware is flashed with the Arduino IDE and Teensyduino, with the CPU speed set to 150 MHz to limit self-heating near the crystal. - Earlier units used a Teensy 3.2 (Wi2) or 3.6 (Q-1). They remain usable: install the firmware and software that match your generation. - Teensy 4.0 shields are not meant for Teensy 3.x boards. The Teensy 4.0 is the recommended route for new builds. - Pre-programmed Teensy 4.0 boards are available, and the firmware is a free download, so one Teensy can be reprogrammed for a different shield. - On the Teensy 3.2 oscillator shield the on-board LED shares its pin with the frequency input, so it stays lit when the board is plugged in and the Blink example shows nothing. This is normal. Source: openQCM support archive (7 threads) ### How far can the crystal be from the electronics, for example through a chamber feedthrough? *Applies to: all instruments* The crystal signal is a low-power signal at several megahertz. Long leads act as antennas, add capacitance and can make an oscillator unstable or lock onto the wrong frequency, so keep the distance as short as you can. - **Sensor module or Holder on a USB 3.0-type extension** : about 1 m has worked well, and up to about 2 m with a slight increase in noise. - **Bare wires from a board to the crystal** : keep them as short as possible, ideally a few tens of centimetres or less, with the shield tied to the openQCM ground. Do not tie either crystal electrode to the shield. - Several metres, let alone tens of metres, do not work with the standard electronics. If distance is unavoidable, move the electronics next to the crystal and extend the digital USB link instead. On Q-1 and NEXT the live resonance curve shows signal quality and interference. Only the crystal needs to be in a magnetic field or chamber; the electronics can stay outside. Source: openQCM support archive (17 threads) ### How do I connect a sensor module, Holder or custom cell to my own electronics or analyser? *Applies to: Q-1, Wi2, Holder* The Q-1/Wi2 sensor module and the passive Holder carry no active circuit in the crystal path. Their USB 3.0-shaped connector (not a USB interface) brings out: - two **crystal lines** , QCM IN and QCM OUT (also labelled SENS− and SENS+); - the I²C lines (SDA, SCL), supply and ground for the temperature sensor. For frequency only, the two crystal lines and ground are enough. Pin orders differ between the USB connector and the Holder gold pads, so use the pinout in the Holder manual or ask support for the sensor-module schematic, and check every line with a continuity tester. A short typically makes the board switch off. The Q-1 shield has footprints for two SMA connectors, one per crystal electrode, for a custom cell; they serve one crystal, not two channels. The circuit has no polarity, and running it without a crystal causes no harm. Use short, shielded, matched leads: unbalanced or long wiring distorts the sweep and has even made a 10 MHz crystal read a spurious frequency. Source: openQCM support archive (28 threads) ### Are schematics, CAD files and source code available to modify or repair my instrument? *Applies to: all instruments* Yes. openQCM is open hardware and open-source software. - **Firmware and software** source code can be downloaded from the website. - **Manuals** describe electronics, bill of materials, printed parts and assembly. - **On request** from support: STL files of the printed parts, STEP models of modules, cells and the 14 mm holder, drawings of covers and windows, a 3D model of the crystal, and schematics of the Q-1, NEXT, Teensy shield and Holder. Users have used these files to make windows in fused silica or CaF₂, covers with extra ports, enclosures for climate chambers, and parts in other materials. The electronics evolve, so files may differ slightly from your unit; ask if anything is unclear. If a downloaded archive does not open or slice correctly, download it again. Documentation is released under a CC BY-NC-SA licence. Files for concept studies that never became products are not available. Source: openQCM support archive (30 threads) ### Should I choose 5 MHz or 10 MHz crystals? *Applies to: all instruments* It depends on what limits your experiment. - **10 MHz** has four times the mass sensitivity per unit area. Over the 0.196 cm² active area of current crystals, 1 Hz corresponds to about 0.9 ng, against about 3.5 ng at 5 MHz (Sauerbrey constants 226 and 56.6 Hz·cm²/µg). Choose it to resolve very small mass changes. - **5 MHz** has a larger dynamic range: it tolerates thicker or heavier layers before the resonance is lost. On Q-1 and NEXT it also offers more overtones, up to the 9th against the 5th for 10 MHz, which helps viscoelastic analysis. If 10 MHz crystals saturate or lose the signal, for example with heavy mineral scaling, thick drop-cast films or particle deposits, switch to 5 MHz. Both frequencies fit all openQCM sensor modules and holders. Source: openQCM support archive (3 threads) ### Where can I clamp, glue or wire the crystal in my own holder? Can I solder to it? *Applies to: all instruments* Only near the rim. The thickness-shear vibration is strongest at the centre and almost zero at the edge, so anything touching the electrode area damps the resonance. That is why openQCM contacts wrapped electrodes with spring pins at the rim. - Keep clamps, gaskets or adhesive within about 1.5 mm of the outer edge, and leave the electrode area free on both faces. - A rigid two-component adhesive applied sparingly at the circumference works best. Soft double-sided tape can damp the crystal or add spurious resonances. - **Avoid soldering.** The electrode films are only nanometres to a few hundred nanometres thick, and soldering heat easily lifts them. Use spring contacts or a conductive silver or gold epoxy instead. - Never let a coating or adhesive bridge the contact pads. Do not glue a chip or substrate onto the crystal either: deposit a thin film of that material instead. - Do not put a Peltier element in direct contact with the crystal; mount the holder on a thermally coupled plate. Covering the rim shifts the baseline frequency, but not the mass-induced shifts. A STEP model of the crystal is available for holder design. Source: openQCM support archive (13 threads) ### I am designing my own QCM cell. How should I seal the crystal without stressing it? *Applies to: all instruments* The most reliable approach is the one used in openQCM modules: clamp the crystal between two soft O-rings, one below and one above. - Use soft FKM (Viton) O-rings of the same type as the openQCM spares, about 11 mm inner diameter for 14 mm crystals. - Provide fine height adjustment of the top part over a few tens of micrometres. Too little pressure leaks; too much stresses the quartz and causes drift. - Keep top and base coplanar with mechanical guides. - Make spring-contact height adjustable so the pins sit level with the lower O-ring. - An inlet low on the side wall and an outlet at the top give cleaner liquid exchange and fewer trapped bubbles. Inlet stubs need enough length to hold the tubing. Silicone gaskets pressed flat on the crystal often leak or break it. If O-ring bending bothers you, stacking two standard O-rings is better than one thick gasket. The standard cells are not pressure vessels; STEP files of openQCM cells can be shared as a starting point. Source: openQCM support archive (2 threads) ### My crystal cracks, or looks tilted, when I close the NEXT fluidic module. What should I do? *Applies to: NEXT* The quartz plate is only a few hundred micrometres thick. It usually breaks because it is not centred in its seat or because the module is closed unevenly. - Lay the crystal flat and centred, contact side down on the spring contacts, and check that both half O-rings sit fully in their grooves with nothing trapped underneath. - Press the top cover gently with your fingers so it seats evenly, then tighten the two slotted nuts a little at a time, alternately, until snug. The design limits their travel, so no torque tool is needed; extra force does not improve contact. - A slight tilt before closing means the crystal is off-centre. With the cover closed it should be pressed flat; if not, inspect the seat. If calibration fails with moderate tightening, check orientation and contact cleanliness instead of adding force. Crystals can also crack from overpressure when liquid is pushed into a cell with a blocked outlet, which pump-out operation avoids. If you keep breaking crystals, send support a photo of the module. Source: openQCM support archive (4 threads) ### Can I use crystals from other manufacturers, or 1-inch crystals? *Applies to: all instruments* Yes, if they match the openQCM sensor format: - **14 mm blank** (13.7–14 mm crystals fit); - **wrapped electrodes** , with both contacts on the back face, because the instruments contact the crystal from below; - a 5 or 10 MHz fundamental, for which the software is set up by default. Sensors made for Q-Sense-type QCM-D instruments in this format work, including SiO₂, Pt and other coated surfaces. Crystals with one contact on each face do not fit the standard modules; a holder can be modified by moving one spring contact, or a custom holder designed. **1-inch crystals** fit the Q-1/Wi2 sensor module only after you remove the white adapter ring that centres 14 mm crystals, and they seal on the large O-ring. They are not recommended: they are harder to seal, cover pressure can deform them so that the instrument locks onto an overtone, and they break more easily under vibration. 5 MHz crystals are thicker than 10 MHz ones, so readjust the lever and check the seal when you change type. Source: openQCM support archive (28 threads) ### Have the openQCM crystal designs changed? Will new crystals fit my setup? *Applies to: all instruments* The electrode mask of openQCM crystals has been revised over time, for example to follow the layout of other common QCM-D sensors. The changes are minor: blank diameter, thickness, overall dimensions and contact layout are unchanged, so new crystals fit the same modules and holders. The current AT5 and AT10 datasheets give the exact dimensions, including the 12 mm front and 5 mm back electrodes. The main improvements are in manufacturing quality, with fewer surface defects and a better quality factor. New crystals behave the same way under spin-coating and other deposition methods. If you receive crystals with visible defects, such as scratches on the electrodes, do not use them for measurements. Contact openQCM support with a description and photos so the sensors can be assessed. When you compare old and new data, remember that older crystals may have a different back-electrode size and therefore a different active area. Source: openQCM support archive (3 threads) ### What happens if the crystal is mounted upside down or misaligned, and how do I recognise it? *Applies to: all instruments* openQCM crystals have wrapped electrodes: the large electrode faces up toward the sample, and the back face, with the small electrode and both contact pads, rests on the pogo pins or spring contacts. Coat or functionalise only the large front electrode. A small flat on the crystal edge helps you find the orientation. If the crystal is upside down, rotated or off-centre, the contacts touch the wrong face or miss the pads. Typical symptoms: - no resonance peak, or calibration fails with an incompatible-peaks message; - very low, distorted or extra peaks; - 0 Hz or meaningless frequency on oscillator devices such as the Wi2; - loss of signal as soon as liquid enters the cell. Open the cell, check orientation, centring and that the crystal lies flat, and look for dirty or worn contacts. If the signal is weak, rotating the crystal by 180° on the same face can improve contact. A misaligned crystal can also leak or crack when the cover is closed. Source: openQCM support archive (38 threads) ### Can openQCM design custom cells, holders or OEM electronics for my application? *Applies to: all instruments* Often, yes; custom development is a regular part of openQCM work. Past examples include: - cells with larger volumes, extra ports or windows for X-ray beams; - holders for 1-inch crystals or crystals with one contact on each face; - immersion probes and racks for several sensor modules; - multichannel frequency platforms and readers for many sensors in a deposition chamber; - thin custom boards for tight spaces and compact modules for small satellites; - electronics retuned for non-standard resonators. Ready-made OEM boards include the TWIN dual-crystal board, the SpaceBug low-power module and the Holder. Because designs are open, STEP files and schematics can also be shared so you can adapt them yourself. Send support a description of your application with sketches: medium, temperature and pressure range, number of sensors, frequency only or with dissipation, size and power budget, data interface and cable lengths. Feasibility and lead time depend on the request. Source: openQCM support archive (44 threads) ### Which version of the 14 mm Quartz Holder do I need, and what can I connect it to? *Applies to: Holder* The Holder is a stack of three FR-4 boards with spring contacts for one 14 mm wrapped crystal, both faces exposed, and an MCP9808 temperature sensor. It comes with a USB 3.0-shaped plug or with gold solder pads. Choose by electronics: - **Without integrated oscillator** (passive): the crystal contacts go straight to the connector. Use it with the Q-1 shield, the Teensy shield, a Q-1 or Wi2 main unit in place of the sensor module, or an impedance analyser. - **With integrated Pierce oscillator** : power it with 3.3–5 V and read a square-wave output at the crystal frequency with a frequency counter, oscilloscope or microcontroller timer input. Do not connect it to the Q-1 or Teensy shields: two driving circuits conflict. Both measure frequency; dissipation needs the passive version on a Q-1 shield. The solder-pad version suits feedthroughs; the through-hole lets you mount it on a heat sink or cold plate. **Never plug the Holder into a computer USB port** : the pinout is not USB. Source: openQCM support archive (43 threads) ### How do I read the temperature sensor on the Holder? *Applies to: Holder* The Holder carries an **MCP9808 digital I²C sensor** . It is not a PT100, so there is nothing to fit or calibrate. Connect four lines to your microcontroller: - SDA to SDA - SCL to SCL - supply (3.3–5 V) - ground The I²C pull-up resistors are already on the Holder. Do **not** add external pull-ups, because they can stop the reading. The openQCM firmware reads the MCP9808 and sends the temperature together with the frequency; in your own code, any standard MCP9808 library works. Check the pin positions in the Holder manual, because the USB-shaped connector and the gold pads use different orders. If you prefer an analogue sensor such as a thermistor or PT100, build a voltage divider on an analogue input and adapt the firmware. The sensor reads the Holder temperature close to the crystal, which is the value to use for temperature compensation. Source: openQCM support archive (2 threads) ### Can the whole crystal be immersed in liquid? Is there an immersion probe? *Applies to: Q-1, Holder* In the standard cells, **no** : only the front face is exposed, and the back face with the contacts must stay dry. Sealing the back with wax or tape would damp the oscillation. To treat the whole crystal, for example to grow a biofilm in a well plate, run peak detection on the clean crystal, incubate, rinse and dry it, then remount and measure. For dipping, an **immersion probe** can be supplied: an elongated FR-4 holder with gold contacts for 14 mm wrapped crystals, which connects to the Q-1 through a USB 3.0 extension and fits a standard electrochemistry beaker. - Use it with Q-1 electronics. Oscillator boards generally cannot keep a fully immersed crystal oscillating. - Both faces are in the liquid, so material on both electrodes adds to the signal; non-specific adhesion on an unfunctionalised face adds background. - The probe has no temperature sensor; ignore the temperature reading. - Calibrate in air first, and check the sealing materials against acidic or aggressive media. Source: openQCM support archive (9 threads) ### Can I still use the HC-48/U crystal holder of the original openQCM? *Applies to: Holder, Wi2* (Legacy: first-generation Arduino-based openQCM, 2015–2017, with the HC-48/U spring-clip holder.) The HC-48/U holder has been discontinued by its manufacturers and is practically unobtainable. This is why openQCM moved to pogo-pin sensor modules and later to the openQCM Holder. Current 14 mm crystals still fit an existing HC-48/U holder, but mounting is critical. The clips must touch only the intended contact pads. On liquid-biosensing crystals the large top electrode comes close to the clips, so liquid can short them and stop the oscillation. Alternatives: - use a current sensor module or the openQCM Holder with 14 mm wrapped crystals, the recommended route for liquids; - wire an existing HC-48/U holder to a Q-1 shield with two short shielded leads, which also gives dissipation; - build your own housing from the CAD files of the original design (the optical window needs CNC machining). Source: openQCM support archive (10 threads) ### How should I set the lever and the pogo-pin height on the Q-1/Wi2 sensor module for a stable baseline? *Applies to: Q-1, Wi2* The **lever** sets how hard the top cover and its O-ring press on the crystal. Insert the cover with the lever at MIN, then move it toward MAX until the cell passes the leak test. - Too little pressure: leaks and poor contact. Too much: stress on the quartz, which causes drift, a weaker response to liquid or no resonance at all. - Use the lowest setting that still seals, find it once before the experiment, and **do not move the lever during a measurement** , because it changes the frequency. When you remount a calibrated crystal, return the lever to the same position. The **small set screw under the module** adjusts the height of the pogo pins. Reach it with the 1.3 mm micro hex key and turn in small steps. The pins should only just protrude above the lower O-ring seat: too high adds stress and noise and can prevent calibration; too low loses contact. The same key sets the height of the window in the top cover. Do not use it to cure a leak; fix the sealing instead. Source: openQCM support archive (14 threads) ### Can I measure several crystals, or a sample and a reference crystal, at the same time? *Applies to: all instruments* Each Q-1, Wi2 or NEXT holds a single crystal. Options for more channels: - **Several instruments on one PC** : each uses its own COM port and its own software instance, for example a NEXT next to a Q-1. Calibrate each one. A blank flow cell in series or in parallel with the functionalised cell gives a reference; account for the transit delay between cells. - **openQCM TWIN** : two matched oscillators, sensor and reference, with their difference available in software and as a TTL output, plus a Peltier controller. Common-mode effects such as temperature cancel to a large extent. It is frequency only and designed for gas and vacuum work. - **Multichannel frequency electronics** : several oscillators read by microcontroller timers, frequency only. Custom multichannel systems have been built on request. - **Multiplexing a Q-1 shield** : RF switches or relays can route one crystal at a time to the board, with firmware and software changes. Contact support before attempting it. Small differences between channels when going from air to liquid are normal. Source: openQCM support archive (16 threads) ### Can I add a humidity sensor to the NEXT, or connect the NEXT electronics to an external holder in a chamber? *Applies to: NEXT* **Extra sensors** : there is no dedicated humidity module. The simplest route is an external USB humidity sensor read by your own script on the same PC, so it shares the computer clock with the NEXT data. Advanced users can also wire a small I²C sensor to the NEXT microcontroller and extend the open-source software; ask support for the connection points before opening the case. **External holder** : the 14 mm Quartz Holder is not plug-compatible with the NEXT electronics, and wiring the NEXT to remote crystal leads is delicate. For chamber experiments it is simpler to place a Holder without USB inside the chamber and keep separate electronics outside: a Q-1 shield with a Teensy for frequency and dissipation, or a Teensy shield for frequency only. Use short, shielded leads. No humidity rating is specified for the electronics, so keep them out of humid chambers. Source: openQCM support archive (3 threads) ### How do I combine QCM with optical measurements, and how do I fill the NEXT optical module without trapping air? *Applies to: NEXT, Q-1, Wi2* - **NEXT optical module** : a PTFE core with a quartz window held mechanically, without adhesives. It suits visual inspection, irradiation, microscopy and spectroscopy such as Raman. The window can be pushed out and replaced with one of the same size for another spectral band; check the seal afterwards. It is not suitable for high pressure. A transmittance curve of the standard window is available from support. - **Q-1/Wi2** : the standard PMMA window is fine for visual checks but not for UV or most spectroscopy. A window in fused silica, quartz or CaF₂ can be made from the cover drawings. The PTFE open cover gives direct access without a window. The extra interfaces around a window pin the liquid and trap air. To fill the optical module: 1. Push liquid in first, pump on the inlet and reservoir on the outlet. 2. Check through the window that the crystal is covered by a uniform film with no bubbles at the edges. 3. Then switch to pump-out, pump downstream of the module, for the experiment. Source: openQCM support archive (18 threads) ### Where does the NEXT measure temperature, and why does it take longer to stabilise with liquid in the cell? *Applies to: NEXT* A 10 kΩ thermistor sits just below the lower face of the crystal, and the Peltier element and heat sink are underneath the sensor holder. The NEXT therefore heats and cools the crystal from the back, through the holder, and the thermistor reads the measurement chamber, not the liquid in your reservoir. Once the cell is filled, the liquid and surrounding parts add thermal inertia, so reaching and holding a new set point takes clearly longer than in air. The fluid channels are machined into the PTFE core, so liquid is brought toward the set temperature as it flows in, but external reservoirs and tubing are not heated. - Let the system settle after filling before recording a baseline. - Pre-condition liquids near the set temperature, or set the cell close to the liquid temperature. - Plan temperature steps with enough holding time. - Temperature control works with the fluidic, optical and pipetting modules. The electrochemistry cell, with its larger volume, needs even longer. - To know the liquid temperature itself, use an independent probe. Source: openQCM support archive (7 threads) ### Which O-rings does the sensor cell use, and can I replace them with another material? *Applies to: Q-1, Wi2, NEXT* The 14 mm sensor cells use **FKM (Viton)** O-rings of about 11 mm inner diameter. Spare O-rings are supplied with the instruments; use those as replacements so the clamping force on the crystal stays as designed. The Q-1/Wi2 module also has a larger O-ring seat for 1-inch crystals. FKM resists a broad range of chemicals and temperatures. For aggressive organic solvents or battery electrolytes, an O-ring of the same size in another elastomer, such as FFKM or EPDM, may suit better; check the manufacturer chemical-resistance chart for your medium. - Replace O-rings that are swollen, flattened or deformed. Swelling causes leaks and slow frequency drift. - Some bending of the crystal under the O-ring cannot be avoided, because the crystal must be clamped yet free to vibrate. If it affects your signal, avoid over-compression rather than looking for a thicker gasket. - The cells and seals are not designed for high pressure. Source: openQCM support archive (9 threads) ### How do I set up the PTFE open cover (pipetting cover) on the Q-1 or Wi2? *Applies to: Q-1, Wi2* The height of the PTFE element must be set once for your sensor module, because printed parts vary slightly. 1. Remove the crystal and place the open cover on the module. 2. Set the lever halfway between MIN and MAX. 3. Press the PTFE element down gently until the two O-rings touch. 4. Lock its height with the three small grub screws, using the micro hex key. Do not overtighten: PTFE deforms. Use only the supplied screws. 5. Remove the cover, mount the crystal, refit the cover and move the lever toward MAX. 6. Check the seal: put a little liquid on the crystal and watch frequency and liquid level. Both should stay stable. If liquid reaches the back of the crystal, dry the crystal and module, loosen the grub screws and repeat. Use small, thin drops of a few microlitres. Thick drops of gels or concentrated solutions can stop the crystal vibrating. Covers with a larger opening can be made on request. Source: openQCM support archive (18 threads) ### What comes with a Q-1 or Wi2, and what else do I need to start measuring? *Applies to: Q-1, Wi2, NEXT* The Q-1 and Wi2 ship with the main unit, the sensor module with its top fluidic cover, a USB cable and the factory test report; check the packing list for the test crystal. Do not order a separate sensor module unless you want a spare. They are powered from the computer USB port, so no external supply, function generator or oscilloscope is needed. The NEXT package is described in its own FAQ. You will also need: - a computer with a USB port, plus the free software and manuals from the website; - spare crystals, 14 mm with wrapped electrodes (liquid-biosensing type for liquid work); - for flow work, a pump and 1.6 mm ID tubing; - optionally, a PTFE-window cover for solvents, the PTFE open cover for pipetting, the micro hex key for fine adjustments, and the Holder for gas or vacuum. A pump is not essential: the closed cell can be filled by hand with a syringe on the outlet tubing. Source: openQCM support archive (15 threads) ### Can I power openQCM electronics from a battery or a power bank? *Applies to: Q-1, Wi2, NEXT, Holder* All openQCM main units run on **5 V DC from USB** , which also carries the data. The Wi2 and Q-1 have no internal battery. A stable 5 V USB source, such as a laptop running on its own battery or a USB power bank, is fine; a laptop on battery is also a quick way to diagnose ground-loop noise. - Do not connect unregulated batteries or other voltages directly to the electronics. A higher voltage can damage the microcontroller, and a lower one, such as 3.3 V on the 5 V input, prevents correct operation. - The NEXT also needs its separate 5 V adapter for the Peltier thermal module. - If you power a Teensy-based shield from an external supply while it is also connected by USB, first separate the Teensy USB and external supply paths (the VUSB–VIN pads), so current cannot flow back into the computer. Running from batteries in a custom setup is a user modification: respect the supply limits in each manual. Source: openQCM support archive (7 threads) ### What are the magnets in the Q-1/Wi2 sensor module, and can I remove them for magnetic-bead experiments? *Applies to: Q-1, Wi2* The sensor module contains small press-fitted magnets. Those in the module body and top cover hold the cover against the base and help the sealing. A tiny metal cylinder under the crystal area improves thermal contact between the cell and the temperature sensor on the proximity board. The magnets can be removed. Support has done so and measured the same frequency and dissipation noise in air and in water without them. If a magnet is hard to extract, do not use pliers: damaging the housing can make the signal unstable. Ask support to remove them instead. Without the magnets the cover aligns differently. Press the cover gently while turning the lever and do not force it if you feel resistance. Always repeat the leak test afterwards. If your samples contain ferromagnetic particles, keep the remaining metal parts in mind and check for any influence with a control run. Source: openQCM support archive (3 threads) ### Can I use crystals with fundamentals other than 5 or 10 MHz? *Applies to: Q-1, NEXT, Wi2* **Q-1 and NEXT** : the electronics sweep from about 1 to 50 MHz, so other fundamentals, such as 3, 6, 9 or 20 MHz, are possible in principle. The standard software is set up for 5 and 10 MHz crystals and their overtones. For other frequencies, edit the calibration sweep and peak-search limits in the open-source Python code (see the FAQ on 6 MHz crystals). Only overtones that fall below about 50 MHz can be measured; with a 25 MHz crystal only the fundamental is available. Coatings that move the resonance far from nominal may need the same adjustment. **Wi2** : the oscillator follows whatever crystal is fitted and the counter reads well above 10 MHz, so no code change is needed. The 8 MHz limit applied only to the original Arduino-based openQCM. Very different frequencies may need different oscillator capacitor values. The crystal must still be a 14 mm wrapped type, or be adapted, to fit the sensor module. Source: openQCM support archive (9 threads) ### Which tubing fits the NEXT fluidic module, and how can I reduce sample volume? *Applies to: NEXT, Q-1, Wi2* All openQCM fluidic cells take soft tubing with **1.6 mm (1/16 in) inner diameter and 3.2 mm (1/8 in) outer diameter** . Tubing with a larger outer diameter does not fit. - **NEXT** : push the tube directly over the small barbs on the module inlet and outlet. The tube elasticity makes the seal, so no fittings are needed. This connection is not meant for pressure, another reason to aspirate rather than inject. - **Q-1/Wi2** : push the tube into the cover. The inlet hole is larger than the outlet; see the user guide if the labels are not visible. The measuring chamber holds only about 50 µL; most of the sample sits in the tubing. Shorter, narrower lines cut the volume needed per experiment considerably and also reduce peristaltic ripple. Push tubes fully home to avoid leaks and trapped air. For solvents or corrosive solutions choose a chemically resistant tubing of the same size. The NEXT internal channels are under 1 mm wide; check them for clogging before each experiment. Source: openQCM support archive (23 threads) ### How do I set up openQCM in a vacuum or thermal-vacuum chamber? *Applies to: Holder, TWIN, Q-1, Wi2* Put only a minimal holder with the crystal inside and keep the electronics outside. The Q-1/Wi2 sensor modules, NEXT modules and instrument cases contain nylon and plastics and are not intended for vacuum. - Use the **openQCM Holder without USB** : three FR-4 layers, gold pads, spring contacts, no plastic housing. Solder wires from the pads to an electrical feedthrough; each sensor needs only a few wires. - Read it outside with a Q-1 shield (frequency and dissipation) or a Teensy shield (frequency only). Keep leads short and shielded, shield to GND. - No pressure rating or outgassing data are published. Qualify the Holder in your own system and bake out only within the ratings of its components; ask support for low-outgassing or high-temperature variants. - The Holder has a temperature sensor but no temperature control. In thermal-vacuum tests temperature usually dominates the signal: run a thermal cycle in the clean chamber first, then subtract that curve from the test data. The through-hole lets you mount it on a cold plate; the TWIN adds a reference crystal. Source: openQCM support archive (45 threads) ### Can I add a wireless link to the Wi2? *Applies to: Wi2* (Legacy: an optional Wi-Fi module based on the ESP8266 was offered for earlier Wi2 units; it is discontinued.) The current Wi2 is **USB-powered and wireless-ready** : power and data travel over the USB cable, and there is no built-in wireless link and no battery. The main board has an expansion header with power, TX and RX for adding a wireless module or a custom board. - A ready-made ESP8266-type board connected to the TX/RX pins is the simplest do-it-yourself route. The schematics, board files and example firmware of the old module, which streamed the frequency with a small web server, are available from support as open hardware. - Firmware differs between Teensy 3.2 and Teensy 4.0 units, mainly in the serial pins used. - Only frequency is transmitted, since the Wi2 measures the fundamental frequency. - If the module seems to send nothing, first check the USB serial output to confirm the instrument is measuring. Use good solder joints: poor ones have corrupted data. The Q-1 has no wireless option. Source: openQCM support archive (17 threads) ### Can I flow gas through the cell, and how do flow, pressure or a gas jet affect the crystal? *Applies to: all instruments* Yes, gas can pass through the same inlet and outlet used for liquids, or you can expose the crystal through an open cover, the pipetting module or a Holder. The flow cells are **not pressure vessels** and have no pressure rating: above a modest overpressure the O-ring seal leaks. Use low-pressure sources such as a small membrane pump or a mass-flow controller. Peristaltic pumps are not suited to gas. Do not use flammable or hazardous gases. - A **steady** flow at cell temperature causes little drift, but more noise than still air. Changes in flow, pressure, gas temperature or humidity shift the frequency, so keep the flow constant and thermally equilibrated before setting the baseline. - Do not aim a strong jet straight at the crystal. The quartz is a few hundred micrometres thick; a high-velocity jet, overpressure or excessive clamping can break it. Increase flow gradually, test on a spare crystal and wear safety glasses. - Compare readings taken before and after exposure under the same flow. Source: openQCM support archive (12 threads) ## Measurements & operation ### What flow rate should I use? *Applies to: all instruments* A typical flow rate is about **0.1 mL/min** , which gives a frequency standard deviation of only a few Hz. The recommended maximum is **1 mL/min** ; higher rates cause larger baseline fluctuations. The exact choice depends on the frequency resolution your experiment needs. Source: https://forum.openqcm.com/d/6-question-about-peristaltic-pump ### Should I aspirate or inject the sample? *Applies to: all instruments* Aspiration was historically recommended to avoid **overpressure and possible leakage** , especially on the older devices. With the redesigned **bayonet sensor module** , injection is also possible — just run some initial checks first. Users report stable operation under injection at ~0.1 mL/min. Source: https://forum.openqcm.com/d/23-aspiration-vs-injection ### Can I use openQCM in vacuum, UHV or cryogenic conditions? *Applies to: all instruments* Yes — QCM is one of the most reliable methods for monitoring molecular-scale mass changes under vacuum and at cryogenic temperatures. Practical notes: - A fully **Teflon (PTFE)** cell limits outgassing; the wetted side is then quartz + gold + Ti, with a nickel-chromium-plated holder. - You can place the **electronics together with the sensor and holder inside the chamber** , or route the connection through a **vacuum USB feedthrough** . - Run a series of **T vs. frequency calibration cycles** before measuring — QCM is very sensitive to temperature but highly reproducible across a thermal cycle (low hysteresis). - A **cold finger** placed <1 mm from the crystal works well; expect a frequency drift until thermal equilibrium. Source: https://forum.openqcm.com/d/11-vacuum ### Can I operate the sensor with a DC offset (e.g. to attract charged particles)? *Applies to: all instruments* The openQCM quartz is **not grounded** . A practical route is to **float the shield** with isolated external supplies and use **opto-isolators** to couple the signal to the Arduino. Validate carefully, as applying a DC bias is outside the standard configuration. Source: https://forum.openqcm.com/d/8-operating-sensor-with-a-dc-offset ### My frequency shift is consistently larger than the Kanazawa-Gordon prediction. Why? *Applies to: all instruments* This is common and usually does not indicate a fault. In our air-to-water calibration the measured shifts are **reproducible across different sensors and devices** — the hallmark of a reliable instrument. When experimental values sit a fixed percentage above the Kelvin-Voigt / Kanazawa-Gordon prediction while remaining **linear and passing through the origin** , it is reasonable to introduce an **instrument calibration constant** that fits the data; the same constant typically holds across different liquids and overtones. Verify the viscoelastic (semi-infinite Newtonian) assumptions apply to your sample. Source: https://forum.openqcm.com/d/20-unexpected-magnitude-of-frequency-shift ### How do I improve reproducibility in liquid measurements? *Applies to: all instruments* Check the usual culprits: **air bubbles** in the chamber, insufficient **thermal stabilisation** (allow ~1.5 h in air first), and inconsistent filling. Fill via aspiration as per the manual, average the last few minutes of each plateau for your baseline, and apply temperature compensation. If discrepancies persist, share your data file with us at [info@openqcm.com](mailto:info@openqcm.com) and we will analyse it. Source: https://forum.openqcm.com/d/35-reproducibility-in-liquid-measurements ### What is the measurement setup when using a network analyzer? *Applies to: all instruments* Each resonance curve is built **point by point by sweeping the frequency** around the fundamental and the overtone harmonics. Once the whole curve is captured in a buffer, the resonance frequency is extracted with a **peak-detection algorithm** . Source: https://forum.openqcm.com/d/41-measurement-setup-using-network-analyzer ### What temperature range can openQCM NEXT control, and how do I reach low temperatures reliably? *Applies to: NEXT* The working temperature range is **25–45 °C** , with heating and cooling by a Thorlabs MTD415T controller. The maximum +45 °C is reached easily, but to approach low temperatures: ensure the lab is not too warm, verify the heatsink is not already hot, and do not ramp down too quickly (excessive power output overheats the heatsink and can trip the safety system that disables active control). For sustained low temperatures, use an external ventilation or cooling system aimed at the heatsink. Source: openQCM NEXT user guide, p.20 ### Which pumping mode should I use to avoid breaking the quartz? *Applies to: NEXT* The suggested mode is **pump-out** , which best avoids leakage problems. In pump-in mode, obstructions or excessively high flow rates can cause overpressure in the chamber and even break the quartz crystal, so use pump-in with great care and keep inlets and outlets free of obstructions. With **peristaltic pumps** you may see a sinusoidal baseline; reduce this "peristaltic effect" by using tubing with a small inner diameter and a low flow rate (the effect can also be removed by post-processing the data). Source: openQCM NEXT user guide, p.21 ### Which pump configuration should I use for fluidic measurements with the Q-1? *Applies to: Q-1* It depends on the pump type: - **Syringe pump** : these generally operate only in infusion mode, so use a *pump-in* (PUMP-IN) configuration. - **Peristaltic pump** : although you can also pump the fluid in, to reduce the risk of leakage openQCM suggests using a *pump-out* (PUMP-OUT) configuration. Source: openQCM_Q-1-user_manual, p.12 ### Do I need to calibrate the Q-1 every time I change the sensor? *Applies to: Q-1* Yes. A calibration procedure must be performed each time the sensor is replaced: 1. In the Setup/Control GUI, open drop-down menu #1 and select "Calibration openQCM Q-1 Device". 2. From drop-down menu #3, select the fundamental frequency of the sensor in use (5 MHz or 10 MHz). 3. Press START. Calibration takes roughly **104 seconds** and the Program Status indicator turns yellow during the process. Calibration is complete when the Infobar shows "Calibration success for baseline correction!" and the Program Status indicator turns green. Source: openQCM_Q-1-user_manual, p.23-24 ### How do I start a real-time frequency and dissipation measurement on the Q-1? *Applies to: Q-1* Once calibrated, select the working frequency (fundamental or an overtone) from drop-down menu #3 — note the resonance frequencies are listed in descending order. Optionally flag "Txt Export Sweep File" (#4) to store raw sweep data. Then press START: the Infobar shows "Please wait, processing early data…" for about **30 seconds** (Program Status yellow), after which it reads "Measuring!" (Program Status green) and the Current Data panel displays live frequency, dissipation and temperature. Source: openQCM_Q-1-user_manual, p.27-28 ### What does the "Set/Reset Reference" button do on the Q-1? *Applies to: Q-1* "Set/Reset Reference" sets a zero baseline line corresponding to the current data, for resonance frequency and dissipation respectively, so the real-time plots are referenced to that point. It works only in Measurement operation mode, and the current reference values are shown under "Reference Settings" in the Info GUI. Source: openQCM_Q-1-user_manual, p.20, 22, 29 ### How can I check that the fluidic chamber of the sensor module is properly sealed? *Applies to: Wi2* You can verify the seal with a simple water test: 1. Connect a tube from the fluidic cover **inlet** to a water reservoir. 2. Connect another tube from the **outlet** to an ordinary syringe. 3. Aspirate liquid with the syringe and stop before the liquid enters the quartz chamber. If the liquid level remains stationary, the chamber is sealed. Otherwise, finely turn the lever counterclockwise toward the **"MAX"** direction to improve sealing. Source: openQCM_Wi2-user_manual.pdf, p.9 ### How should I connect a syringe pump or a peristaltic pump for fluidic measurements? *Applies to: Wi2* The recommended setup depends on the pump type. A **syringe pump** generally operates only in infusion mode, so it should be used in a **pump-in** configuration. For a **peristaltic pump** , the manual recommends a **pump-out** setup to reduce the risk of leakage; pumping in is also possible, but pump-out is advised. Source: openQCM_Wi2-user_manual.pdf, p.10 ### How does the board measure and output the two crystal frequencies and their difference? *Applies to: TWIN* The Teensy 4.0 measures both crystals independently using its QuadTimer4 (TMR4) hardware counters, on pin 6 (B0_10) for one channel and pin 9 (B0_11) for the other, in frequency-counting mode. The two frequencies can be monitored individually or their difference obtained through software. In addition, a dedicated Teensy output pin generates a **TTL signal whose frequency equals the real-time difference** between the reference and sensor crystals, which can be fed to external frequency counters or DAQ systems for hardware-level measurement. Source: openQCM_TWIN_User_Manual.pdf, p.10, 15 ### How does the firmware measure the QCM frequency and log data? *Applies to: SpaceBug* The sample firmware uses hardware timers on the SAMD21: `TCC2` acts as a reference timer that defines a precise **1-second** integration window, while `TCC0` counts the incoming pulses from the QCM sensor during that window. Each loop iteration triggers a conversion via `startConversion()`, waits for the window to complete, reads the RTC timestamp, measures temperature from the thermistor (averaging samples with the Steinhart-Hart equation), and logs the timestamp, temperature, and frequency to a file on the micro-SD card. Serial output runs at **115200** baud. Source: openQCM SpaceBug.pdf, p.24, 25, 33 ### How can I reduce power consumption with deep sleep mode? *Applies to: SpaceBug* To conserve power during idle periods, the SpaceBug can enter **deep sleep mode** using the LowPower library by Rocket Scream Electronics. 1. Include `#include ` at the top of your code. 2. At the end of the `loop()`, call e.g. `LowPower.deepSleep(5 * 60000);` to sleep for the desired interval (5 minutes in this example). 3. In `setup()`, configure the RTC interrupt to wake the microcontroller, e.g. `rtc.enableInterrupt(RTC_INT_ALM);` and `rtc.setAlarmSeconds(0);`. The RV-3028 RTC `_INT` pin (connected to `RX`) wakes the SAMD21 from deep sleep, significantly extending battery life for long-term deployments. Source: openQCM SpaceBug.pdf, p.28, 29 ### Are the overtones measured at the same instant? *Applies to: NEXT, Q-1* No. Both instruments have one synthesiser and one detector, so the frequency sweeps around each harmonic run **one after another** . - **NEXT** (Multiscan mode) reads all available overtones in every multiscan cycle, about 1.4 s per overtone (about 7 s for five overtones): fundamental to the 9th overtone on a 5 MHz crystal, fundamental to the 5th on a 10 MHz crystal. The full cycle is also the default and minimum datalog sampling time. - **Q-1** follows one harmonic at a time, chosen in the software, at about 1.0 s per overtone. For most adsorption, binding and film-growth processes, a few seconds between harmonics is negligible. For very fast events, follow a single harmonic. Source: openQCM Measurement Methodology, p.12; openQCM NEXT user guide, p.9, 27, 30; openQCM_Q-1-user_manual, p.36 ### Can I obtain conductance and susceptance (admittance) spectra from the Q-1 or NEXT? *Applies to: Q-1, NEXT* Not directly. The Q-1 and NEXT are scalar network analysers built around a gain-and-phase detector, not impedance analysers. For each sweep point they record the gain and phase of the signal transmitted through the crystal network. The resonance frequency comes from peak detection on the amplitude curve and the dissipation from its width. You can export the raw sweeps (frequency, amplitude in dB, phase) with the sweep-file export option and convert them to conductance and susceptance using a circuit model of the input network. Users have done this successfully. There are limits. The phase detector cannot distinguish the sign of the phase around ±90°, and it is least accurate near 0°, which can distort the admittance circle. Treat such conversions as experimental, and compare them with a reference impedance analyser before relying on absolute values. Source: openQCM support archive (2 threads) ### How do I fill the flow cell without trapping air bubbles, and how do I get rid of them? *Applies to: all instruments* Bubbles are common in any small QCM cell. On the electrode they push the signal toward the air value, cause sudden jumps (frequency up, dissipation down) and amplify temperature effects as they expand and shrink. - Fill by aspiration (pump-out), slowly at first, and keep the cell full when exchanging liquids instead of emptying it. - Pre-wet inlet and outlet fittings before inserting the tubing. - Degas liquids and do not warm them above the cell temperature: dissolved gas comes out as temperature rises. On the NEXT, set points near 25 °C help. - Priming with isopropanol, then switching to the aqueous liquid, wets the chamber without trapping air (skip this with solvent-sensitive coatings). - Tilt the cell so the outlet points upward if filling is difficult. - Clean the cover: adsorbed proteins make it hydrophobic and favour bubbles. A small bubble away from the electrode usually has little effect. The optical module traps bubbles more easily, so inspect it before measuring. Source: openQCM support archive (11 threads) ### What frequency shift should I expect from air to water, and how can I use it to check my setup? *Applies to: all instruments* The air-to-water step on a clean, bare crystal is the best quick check. Typical approximate values at the fundamental, room temperature: | Crystal | Δf, air → water | | --- | --- | | 5 MHz | about −0.7 kHz | | 10 MHz | about −2 kHz | Dissipation rises clearly. Its absolute value depends on the instrumental definition and software version, so compare it with your own earlier runs or with the factory test report, which includes an air-to-water test. - Wait for a stable plateau, typically about 20 minutes in static water. - Frequency shifts follow the Kanazawa–Gordon relation within some tens of percent and grow roughly with √n across overtones. - A much larger shift suggests a leak, a bubble, a coated or dirty crystal; a much smaller one suggests poor contact or wrong mounting. - For a second check, replace water with a 20–25 % w/w sucrose solution: frequency and dissipation should change clearly again. Repeat the check with each new solvent before measuring coated sensors. Source: openQCM support archive (12 threads) ### Can a QCM measure dust, aerosols, powders or particle deposition? *Applies to: all instruments* Yes, with conditions. A QCM weighs only mass that is **rigidly coupled** to the vibrating electrode in a thin layer. It is not a balance: a filter, a chip or a pile of powder placed on the crystal will not be weighed and may even make the frequency rise. - **Particle size** : as a rough guide, sub-micrometre particles couple well; above about 5–10 µm, sensitivity drops sharply because grains touch the surface at small contact points. - **Load** : particle deposits saturate the crystal earlier than uniform films. Clean or replace it regularly; 5 MHz crystals give a longer useful range. - **Collection** : expose the bare crystal (open cover, pipetting module or Holder), centre the deposit, and prefer natural settling or a gentle impactor flow. Use smooth pumps; pulsations become noise. - **Environment** : humidity and temperature changes mimic deposition. Log both, or use a filtered reference crystal in the same environment. For powders, dissolve or disperse the material and deposit a thin film instead. Quantitative particle mass needs comparison with a reference sampler. Source: openQCM support archive (18 threads) ### How long should I wait before measuring, and why does the baseline not return to its starting value after rinsing? *Applies to: all instruments* Most early drift is **thermal equilibration** of electronics, cell, crystal and liquid. As a guide, allow about 10 minutes in air and about 20 minutes in static liquid, and longer after power-on, liquid exchange or a temperature change. Instruments without temperature control can need up to an hour. Bring liquids to the cell temperature before injecting them. If the frequency does not come back to the initial baseline after rinsing, something usually changed: - the deposit was not fully removed, or the surface was permanently modified; - micro-bubbles or incomplete liquid exchange; - a different temperature than at the start; - O-ring swelling or slow stress relaxation, which can release suddenly; a gentle tap on the cell above the crystal can help; - spikes from moving tubes or swapping reservoirs. Make connections far from the module. Compare plateaus recorded in the same liquid at the same temperature. Differences of a few hertz are within normal repeatability and negligible for shifts of tens or hundreds of hertz. Source: openQCM support archive (13 threads) ### Is openQCM suitable for protein, antibody and bacteria binding experiments? *Applies to: Q-1, NEXT* Yes. The Q-1 and NEXT measure frequency and dissipation in liquid and have been used in many published studies of protein adsorption, antibody–antigen immunoassays, biofilms and bacteria detection. The openQCM website keeps a list of publications. - Use gold liquid-biosensing crystals, or compatible functionalised 14 mm wrapped crystals. - Run peak detection on the clean crystal, establish a stable buffer baseline, then set the reference before injecting. - Expect binding shifts from a few to tens of hertz. Control temperature, bubbles and flow, and allow time for binding. - Return to the same buffer after each step, so binding is read between baselines in the same liquid. - For soft layers such as cells and biofilms, use dissipation and, on the NEXT, several overtones. The Wi2 can follow binding in aqueous buffer by frequency alone, but without dissipation you cannot tell mass from viscoelastic changes. Source: openQCM support archive (5 threads) ### When must I repeat the calibration (peak detection), and can I do it with a coated crystal or in liquid? *Applies to: Q-1, NEXT* In the Q-1 and NEXT software, **calibration is peak detection** , not a mass tare. A wide sweep locates the fundamental and overtones of the mounted crystal, and later sweeps are centred on those peaks. - Calibrate each time you mount a different crystal, with the correct nominal frequency (5 or 10 MHz) selected. - Do not recalibrate when you change solutions or add analytes on the same crystal. Mass changes are read relative to your reference. - To functionalise outside the instrument, calibrate the bare crystal first, then remount it without recalibrating and with the lever in the same position. - Recalibrate if the resonance has moved out of the sweep window: cut-off warnings or implausible data are the signs. **Air or liquid?** A clean, dry crystal in air gives the most robust result. Recent software versions can also find the peaks with liquid or a coating present, provided at least the fundamental stands out clearly; check the result. A heavy gel or thick coating that hides the peak cannot be calibrated by any software. Source: openQCM support archive (39 threads) ### Why do my absolute dissipation values differ from theory or from another instrument? *Applies to: NEXT, Q-1* Q-1 and NEXT take the frequency by peak detection on the swept response, without curve fitting, and report an **instrumental dissipation** from the peak width at a calibrated level below each peak. It tracks changes (ΔD) reliably but is not numerically identical to ring-down or fitted D = 1/Q. Common reasons for differences: - **Definition and software version** : the dissipation definition changed across Q-1 software versions, so absolute D depends on the version used. Note it with your data. - **Truncated peak** : if a broadened peak extends beyond the sweep window, D is underestimated; cut-off warnings signal this. - **Asymmetric peaks** in viscous liquids. - **Detector range** : strongly damped crystals push the detector toward its non-linear region. To compare with theory, measure a Newtonian reference such as water–glycerol and derive a scaling factor. Enable the raw sweep export so you can reprocess data later. Source: openQCM support archive (9 threads) ### How should I deposit droplets for drop-casting or evaporation measurements? *Applies to: all instruments* - **Position** : deposit at the centre of the active electrode. Sensitivity is highest there and falls toward the edge, so a drop that spreads beyond the active area gives a lower apparent mass. - **Size** : keep drops small and add several aliquots if needed. The sensor probes only the first few hundred nanometres of liquid, so a drop simply has to cover the electrode. Never let liquid reach the crystal edge or the contact side. - **Low-surface-tension solvents** spread and wander; holding the drop with the pipette tip helps. - **Reading** : Sauerbrey does not apply while liquid is present. Read the mass only after full evaporation, once frequency, dissipation and temperature have plateaued. Solvent can stay trapped in a film long after the visible liquid is gone. Uneven coffee-ring deposits give results that differ from a uniform film. A dissipation value apparently below the bare-crystal level usually means the process is incomplete or the clamping changed. Frequency alone measures the dry residue; dissipation helps follow the drying itself. Source: openQCM support archive (9 threads) ### How can I measure the swelling of a thin film in a solvent? *Applies to: NEXT, Q-1* A recommended protocol, using the same crystal throughout: 1. Bare crystal in air: record each overtone as reference. 2. Bare crystal in the pure, degassed solvent: compare the shift with the Kanazawa–Gordon prediction to validate mounting and filling. 3. Coated crystal, dry, in air: if Δf_n/n is the same on all overtones and dissipation stays low, the film is rigid; get the dry thickness with Sauerbrey, preferably from the 3rd overtone. Otherwise use a viscoelastic model. 4. Coated crystal in solvent: record frequency and dissipation on several overtones until the signals plateau, then fit a viscoelastic (Voigt) model for the wet thickness. 5. Compute the swelling ratio h_wet/h_dry. If frequency *rises* and dissipation *falls* in solvent, the film may be dissolving rather than swelling. Confirm with an independent method, such as ellipsometry, on a witness sample. Multi-overtone data come from the NEXT; on a Q-1 repeat the run on each harmonic. Source: openQCM support archive (1 thread) ### Can openQCM be used as a film-thickness monitor in vacuum deposition? *Applies to: Holder, Wi2, Q-1* Yes. For thin rigid films, such as metals, oxides or nitrides from tens to a few hundred nanometres, thickness follows from the frequency shift: the Sauerbrey equation gives the areal mass, and dividing by the film density gives the thickness. For thick or acoustically mismatched films a Z-ratio correction is usually applied. A typical setup is the openQCM Holder inside the chamber, wired through a feedthrough, with frequency-only electronics (Teensy shield or Wi2 board) outside. Points to plan for: - Radiant heat from evaporation sources shifts the frequency. Allow thermal equilibrium, or mount the Holder on a cooled plate using its through-hole. Water-cooled crystal heads are not offered. - Use short, shielded wiring. - The thickness calculation must be added to the open software or done afterwards. - Replace the crystal well before the saturation limit; 5 MHz crystals accept thicker deposits. Source: openQCM support archive (9 threads) ### The frequency rises when I inject my sample. Besides mass loss, what can cause it? *Applies to: all instruments* A frequency increase does not always mean material left the surface. Check these causes: - **Bulk liquid effect** : in liquid the frequency depends on the density and viscosity of the medium. A sample less dense or less viscous than the previous liquid, for example one containing ethanol, raises the frequency with no binding at all. - **Air bubbles** on the electrode or at the O-ring: frequency rises and dissipation usually drops. - **Desorption** of weakly bound material during rinsing or pumping. - **Stress relaxation** in the O-ring or cell, or a temperature change. - **Loosely coupled** particles, powders or thick soft layers, which do not follow the crystal motion. Return to the same buffer after each step, so binding is read as the difference between baselines in the same liquid, and always look at dissipation and temperature alongside frequency. Source: openQCM support archive (5 threads) ### Why is the measured fundamental not exactly 5,000,000 Hz or 10,000,000 Hz? *Applies to: all instruments* Every crystal has its own resonance frequency within a manufacturing tolerance: the datasheets give ±7 kHz for 5 MHz and ±5 kHz for 10 MHz crystals. Mounting pressure, temperature, the medium and any coating shift it further. The software reports the actual frequency of the resonance peak, which is the right value to track; for Sauerbrey calculations use the nominal fundamental in the sensitivity constant. A reading far from nominal points to a different problem, for example about 6 MHz or 16 MHz for a 10 MHz crystal. Usual causes: - the wrong nominal frequency selected, or software for a different instrument; - a crystal mounted upside down or poorly contacted; - an oscillator locked onto another mode, often because of long or poor wiring. Source: openQCM support archive (2 threads) ### Which openQCM setup should I use for gas, vapour or VOC sensing? *Applies to: all instruments* A bare gold crystal responds only to mass that sticks to it. For a specific gas or vapour, coat the electrode with a sensing layer, such as a polymer, nanofibres, peptides or a metal–organic framework, and keep it thin. Frequency alone is enough for most gas work. - **Own chamber** : the 14 mm Quartz Holder inside, wired to a Teensy shield (frequency) or Q-1 shield (frequency and dissipation) outside. Both crystal faces see the gas. - **Standard cells** : Q-1, Wi2 and NEXT flow cells can carry gas or vapour at near-atmospheric pressure. Use the PTFE window rather than PMMA with organic vapours or corrosive gases. - **Open exposure** : the PTFE open cover or NEXT pipetting module. - **Reference** : an uncoated reference crystal, as on the TWIN, cancels much of the temperature and humidity effect. Record a temperature–frequency curve first and keep humidity stable. For flammable gases or high pressure, put only the sensor in a dedicated chamber with the electronics outside. Source: openQCM support archive (34 threads) ### In gas-phase sensing, why does the frequency not return to baseline after the first exposure? *Applies to: all instruments* The first exposure of a fresh coating often leaves an **irreversible deposit** : strongly bound molecules or a chemical change of the layer. The baseline then shifts permanently. If the shift is the same on all overtones after dividing by the overtone number, the deposit behaves as a rigid mass. Later exposures are usually reversible, but their amplitude can shrink cycle by cycle as adsorption sites saturate, and it can depend on that first deposit. - Condition the coating with one or more preliminary exposures before collecting data. - Keep gas delivery identical between runs: same flow or static exposure, same humidity, same temperature. - Record dissipation too. It helps distinguish rigid adsorption from swelling or softening of the layer. Source: openQCM support archive (1 thread) ### Which harmonic should I follow, and why are the higher overtones smaller and noisier? *Applies to: Q-1, NEXT* - The **fundamental** usually has the strongest peak and the best signal-to-noise ratio, a good default for monitoring. - The **3rd overtone** is widely used because it is less affected by mounting stress and edge effects. - Comparing several overtones, normalised as Δf_n/n, tells you whether a layer is rigid or viscoelastic. Mass sensitivity per Δf_n/n is the same on every overtone; higher overtones probe a thinner region near the surface. Available harmonics: up to the 9th with 5 MHz crystals, up to the 5th with 10 MHz. The NEXT reads all available overtones in every multiscan cycle, about 1.4 s per overtone (about 7 s for five overtones); the Q-1 follows the harmonic selected for the run. Peak amplitude falls at each higher harmonic: surface displacement is smaller, losses grow with frequency and coupling to the electronics changes across the band. Near the top of the range, such as 50 MHz, signals are noisier. That is why the software sets the dissipation cut-off per harmonic. Crystals from different batches or makers can also behave differently. Source: openQCM support archive (7 threads) ### How do humidity and salt water affect my measurements? *Applies to: all instruments* **Humidity** : quartz and gold surfaces adsorb water, which is why QCMs make good humidity sensors. The nylon housing and FKM O-rings of a sensor module also take up water, which changes the stress on the crystal and causes drift. In air, a slow frequency rise with stable dissipation usually means volatile components are evaporating; a fall with rising dissipation usually means the sample is absorbing moisture. Purge with dry nitrogen to check. For air-quality or gas work, the O-ring-free Holder and a reference crystal reduce the effect. **Saline media** : water, buffers and high-salinity solutions are routine. PTFE and FKM handle them well. Two things become critical: - good sealing, verified with the leak test; - cleaning after any leak, because salt residue on the proximity board disturbs the crystal contacts and the temperature sensor. No humidity rating is specified for the electronics. For humidity-chamber work, put only the sensor or holder inside and keep the electronics outside with short leads. Source: openQCM support archive (14 threads) ### Can I run long experiments, for example several days with cells or biofilms in an incubator? *Applies to: Q-1, Wi2, NEXT* Yes. The hardware imposes no time limit, and multi-day bacterial, biofilm and cell experiments have been run. - **Q-1 and Wi2** only monitor temperature. For a stable temperature, place the whole instrument, sensor module and main unit, in an incubator; a humidified 37 °C, 5 % CO₂ atmosphere is fine. Switch the incubator on before putting the device inside, keep the door closed during measurements, and check the incubator for electrical interference. - **NEXT** controls the cell itself (25–45 °C). Keep the NEXT itself on the bench at room temperature, not in a warm incubator. - Expect an initial drift while everything reaches temperature. Record the bare-medium baseline before inoculation and repeat media changes the same way each day. - Disable PC sleep and power saving, choose a datalog interval suited to your process, and turn off sweep-file saving unless you need raw curves. Files get large. - Keep bubbles off the electrode and the reservoir full. Source: openQCM support archive (13 threads) ### Can I measure viscous liquids or heavily damped samples, and can the Wi2 work in liquid? *Applies to: Wi2, Q-1, NEXT* Damping lowers and broadens the resonance, so signal-to-noise falls as viscosity or film loss rises. In a Newtonian liquid, frequency and dissipation shifts scale with the square root of density × viscosity (Kanazawa–Gordon), which sucrose or glycerol–water standards reproduce well. - **Wi2 and other oscillator electronics** work well in water and aqueous buffers, for example for antibody–antigen binding. The oscillator must sustain the vibration itself, so in highly viscous liquids, thick hydrogels or heavy coatings it can stop or jump to a spurious mode; the reading then jumps or drops to zero. Without dissipation you also cannot separate mass from viscoelastic effects. - **Q-1 and NEXT** interrogate the crystal passively and keep tracking a damped resonance, with dissipation. They are the better choice for viscosity work. Very viscous samples, such as resins or honey, can stop the resonance completely. Control temperature closely, because viscosity changes strongly with it, and test your own sample. Source: openQCM support archive (11 threads) ### Is my instrument calibrated for mass? Is there a standard calibration curve or test report? *Applies to: all instruments* No universal mass calibration curve is supplied, because the frequency–mass relation depends on the sample: rigidity, viscoelasticity, uniformity and the surrounding medium. For thin rigid films the Sauerbrey equation converts frequency to mass directly from the crystal constants; over the 0.196 cm² active area, 1 Hz is about 3.5 ng at 5 MHz and about 0.9 ng at 10 MHz. For other samples, build an empirical calibration against an independent method. Each device is checked before shipping with a standard performance test, an air-to-water transition plus baseline noise, and comes with a test report. If you have lost it, ask support and give the serial number on the bottom of the instrument. You can repeat the same test at any time to verify your unit. The "calibration" button in the Q-1 and NEXT software is something else: the peak-detection step for each crystal. Source: openQCM support archive (4 threads) ### I lost the signal after depositing a coating. Has the crystal saturated, and what can I do? *Applies to: all instruments* Probably. Every layer damps the resonance. Beyond a point the peak becomes too weak or leaves the sweep window, and you see the frequency drop to zero, a sudden jump of hundreds of kilohertz, a calibration that cannot find the fundamental, or cut-off warnings. - For rigid, uniform films the nominal limit is about 1 % of the resonance frequency (see the FAQ on maximum mass). Stay well below it for a linear response. - Soft, porous, wet or viscous layers saturate much earlier, because they absorb acoustic energy. - Oscillator electronics (Wi2, Teensy shield, Holder with oscillator) usually stop earlier than the sweep electronics of Q-1 and NEXT. - 5 MHz crystals tolerate about twice the areal mass of 10 MHz crystals. Start with very thin layers and add material in small steps. Make sure the layer adheres well: a loosely bound layer does not move with the crystal and is not weighed correctly. Source: openQCM support archive (12 threads) ### Why is the signal noisier with the pipetting module or open cover, and how can I improve it? *Applies to: NEXT, Q-1, Wi2* In an open cell the liquid has a **free surface** . Small vibrations, air currents and evaporation move it, and the movement reaches the sensor as baseline noise or drift, sometimes with intermittent bandwidth warnings. Partly filled wells and large volumes make it worse. - Fill the well completely, then place a cover that touches the liquid, such as a glass coverslip or the module lid. This removes the free surface and stops evaporation. - If you cannot cover it, use the smallest volume that covers the electrode. - Keep the NEXT pipetting module horizontal; temperature control also works with it. - Allow time for thermal equilibrium after adding liquid. If the expected signal is hundreds of hertz, the residual noise may be negligible. When samples can be exchanged by flow, the closed cell gives better signal-to-noise: stop the flow and measure static, or fill it by hand with a syringe on the outlet. Open covers suit drop-casting, evaporation and exposure to air or vapour. Source: openQCM support archive (27 threads) ### What should the resonance curve look like on the Q-1 or NEXT? *Applies to: Q-1, NEXT* In measurement mode the amplitude plot should show one clear, roughly bell-shaped peak for each harmonic, with a phase curve that changes smoothly through it. Calibration in air should find the fundamental and all expected overtones. - In liquid or with soft films the peak becomes lower and broader and can be slightly asymmetric. This is normal. - A slight tail on the right side of a very sharp peak can come from the high crystal Q combined with the sweep speed. It does not affect the resonance frequency, can affect dissipation slightly, and is reduced in newer software. Be concerned if you see several peaks, no peak, only one flank of a peak, a very low or jagged curve, or noise spikes. These point to bad contact, a wrongly mounted crystal, overload or interference, and the data should not be used until the cause is fixed. Source: openQCM support archive (4 threads) ### How do I get a stable baseline under flow? *Applies to: Q-1, Wi2, NEXT* openQCM does not supply pumps; a peristaltic pump or a bidirectional syringe pump used in pump-out mode is recommended. Typical flow rates are about 0.1–1 mL/min, with lower rates (tens of µL/min) common for binding assays. Approach flow in steps: 1. Fill the cell and wait for a steady state in static liquid. 2. Start at a low flow rate and wait for a new steady state. 3. Increase the flow only if needed. - Starting or stopping flow produces short transients in frequency and dissipation from pressure, shear and heat transfer. They are not mass changes; wait for them to settle or compare readings with the pump stopped. - Peristaltic pumps add a periodic ripple. Use small-bore, thick-walled pump tubing, low speed, and keep the pump away from the module; the remaining ripple has a known period and can be filtered afterwards. - If frequency rises and dissipation falls after the flow starts, bubbles have entered. Dissipation is often less sensitive to flow noise than frequency, because it comes from the curve width rather than the peak position. Source: openQCM support archive (34 threads) ### How should I run temperature-dependent measurements on the NEXT? *Applies to: NEXT* When temperature changes, frequency and dissipation shift for two reasons: the crystal temperature coefficient and, more strongly in liquid, the change in liquid viscosity and density. Part of the response is therefore real physics that no software can simply subtract. Proceed empirically: 1. Use **step-and-hold** set points, letting the cell equilibrate at each step, or a very slow ramp. When ramping down, go in steps so the heat sink does not overheat. 2. Record the bare sensor, dry or in plain buffer, over the same sequence. 3. Run a matched control, such as buffer or the sample without its active component, and subtract it. Stay within the 25–45 °C working range. The software logs temperature together with frequency and dissipation on all harmonics; because the code is open, programmed temperature sequences can be added. Highly lossy samples, such as whole blood, can over-damp the resonance. Source: openQCM support archive (2 threads) ## Electrochemistry (EQCM) ### Does the NEXT eQCM module include a potentiostat? *Applies to: NEXT* No. The e-QCM module does **not** provide electrochemical analysis on its own; it is a specialized cell designed to interface openQCM NEXT with a wide range of commercially available third-party potentiostats. You connect your own potentiostat to run methods such as cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy, while the module enables simultaneous high-precision QCM measurements correlated with the electrochemical data. Source: openQCM_NEXT-Electrochemistry-Module, p.9 ### What are the specifications of the NEXT electrochemistry module? *Applies to: NEXT* The NEXT electrochemistry module is still an **experimental prototype** : the figures below come from its preliminary user guide (v1.0, May 2025) and may change. The eQCM cell has a chamber volume of about **15 ml** and maximum dimensions (L × W × H) of 6 × 7 × 6 cm, weighing about 90 g. Materials include a PTFE (Teflon) reservoir and cover, Viton (FKM) O-rings, a quartz cylinder, an anodized aluminium sensor holder, and a PLA plastic case. It works with the same NEXT quartz sensors (5 and 10 MHz, 14 mm blank, wrapped) and supports multi-overtone frequency and dissipation measurement via the network analyser interface. Source: openQCM_NEXT-Electrochemistry-Module, p.8 ### How do I orient the quartz sensor in the electrochemistry cell? *Applies to: NEXT* The quartz crystal has two distinct sides: the top side carries the **larger gold electrode (sensing side)** which must face **upward** , because it serves as the working electrode in contact with the solution; the bottom side has the smaller electrode pattern that interfaces with the holder's electrical contacts. Using **plastic-tipped tweezers only** , place the crystal flat in its socket with the larger electrode up and the notch pattern matching the reference figure. Verify it sits completely flat with no lateral movement, since misalignment can cause crystal breakage when installing the PTFE reservoir. Source: openQCM_NEXT-Electrochemistry-Module, p.14-15 ### How do I assemble the NEXT electrochemical QCM cell? *Applies to: NEXT* Follow the sequence in the manual: 1. **Place the sensor** in the holder with the larger electrode facing up. 2. **Install the quartz cylinder** into the PTFE reservoir: lower it vertically onto the seating rim so it self-aligns with minimal force (wear gloves and safety glasses). 3. **Install the pre-assembled reservoir unit** onto the quartz holder, aligning its three anti-rotation wings (spaced 120°) with the corresponding slots; lower it horizontally until flush. 4. **Install the fixing ring** using its bayonet mechanism, rotating counterclockwise only until you feel moderate resistance — do not over-tighten. 5. **Install the PTFE cover** , lowering it onto the cylinder with gentle, uniform vertical pressure. If any step meets resistance, stop and recheck alignment rather than forcing components. Source: openQCM_NEXT-Electrochemistry-Module, p.14-22 ### How do I connect the working, reference, and counter electrodes on NEXT? *Applies to: NEXT* The counter and reference electrodes are inserted through the designated fittings in the PTFE cover, which has two primary ports of 6.2 mm diameter for standard reference and counter electrodes (plus two smaller auxiliary ports for fluid handling). Two fitting adapters for 4 mm and 6 mm probes are included for longer electrodes. The **working electrode** connects via a 2 mm Female Banana Socket on the front of the module; use the included 2 mm green Male Banana Plug, soldered to a cable, to connect to your potentiostat's working-electrode terminal. Source: openQCM_NEXT-Electrochemistry-Module, p.22, 25 ### How do I install the assembled electrochemistry cell onto openQCM NEXT? *Applies to: NEXT* The module has four insertion pins at its base (two per side) that mate with four receptacle slots in the PTFE housing. Install in three phases: 1. **Alignment** — position the module above the housing and visually verify the four pins align with their slots. 2. **Initial insertion** — gently lower the module, guiding the pins into their slots with even pressure; stop at first engagement and do not force it if you feel resistance, recheck alignment instead. 3. **Complete seating** — use the sliding mechanism to guide it to the stop point without tilting, ensuring reliable electrical contact. Improper installation can cause poor electrical contact or damage the connector pins or housing. Source: openQCM_NEXT-Electrochemistry-Module, p.24 ### Why must the electrochemistry cell be completely filled with electrolyte? *Applies to: NEXT* After assembly it is essential to fill the cell completely, up to the electrochemical probe insertion ports. Any free air–liquid interface introduces significant baseline noise and spurious oscillations that can mask or distort the QCM signal. To get reliable data: fill slowly and methodically to avoid trapping bubbles, use slightly positive pressure to displace trapped air, consider a degassed solution, keep the temperature stable to avoid convection, and verify the fill level periodically during long experiments where evaporation may occur. Source: openQCM_NEXT-Electrochemistry-Module, p.27 ### Which instrument does the Electrochemistry (e-QCM) module work with, and does it include a potentiostat? *Applies to: Q-1* The e-QCM module is specifically designed for full compatibility with the **openQCM Q-1** ; you simply replace the standard Q-1 sensor module using the same mounting interface. The module itself does **not** provide electrochemical analysis — it is engineered to interface with a wide range of commercially available third-party potentiostats, supporting methods such as cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy provided by the connected potentiostat. Source: openQCM_Electrochemistry-Module-User_Manual, p.11-13, 26 ### How should the quartz crystal be oriented in the Q-1 EQCM cell? *Applies to: Q-1* In the electrochemical cell the quartz crystal serves as both the QCM resonator and the working electrode, so orientation is critical. Place it so the **top side with the larger gold electrode faces upward** (toward the solution) to act as the working electrode, while the smaller electrode pattern on the bottom interfaces with the contact pins. Use plastic-tipped tweezers, verify the crystal sits completely flat with no lateral movement, and keep the sensing surface clean — misalignment can break the crystal when the PTFE reservoir is installed. Source: openQCM_Electrochemistry-Module-User_Manual, p.16-17 ### How do I connect the working, counter and reference electrodes on the Q-1 EQCM module? *Applies to: Q-1* The counter and reference electrodes are inserted through the designated fittings in the PTFE cover, which has two primary ports (6.2 mm diameter) for standard reference and counter electrodes, plus two smaller auxiliary fluid ports; two fitting adapters for 4 mm and 6 mm probes are included. For the **working electrode** , the module has a 2 mm green female banana socket on its side panel; solder the supplied 2 mm green male banana plug to a cable and connect it to the potentiostat's working-electrode terminal. Source: openQCM_Electrochemistry-Module-User_Manual, p.24, 26 ### How do I connect the EQCM module to the Q-1, and how do I know the connection is good? *Applies to: Q-1* Replace the standard Q-1 sensor module with the electrochemical module using the same mounting interface, and connect it to the Q-1 central unit via the standard **USB3** connector. A successful electrical connection is confirmed by a **blue LED** lighting up on the module. **Important** : connect the module only to the openQCM Q-1 central unit — never directly to a PC or other USB port, as this could electrically damage the module. Source: openQCM_Electrochemistry-Module-User_Manual, p.26 ### How tight should the fixing ring be when assembling the Q-1 EQCM cell? *Applies to: Q-1* The fixing ring uses a bayonet locking mechanism. Lower it over the quartz cylinder, then make small clockwise/counterclockwise movements so the bayonet slots engage the alignment pins on the quartz holder. To secure, rotate the ring **counterclockwise only until you feel moderate resistance** — this indicates optimal compression of the sealing elements. Do not fully tighten: over-tightening introduces unnecessary stress on the assembly. Source: openQCM_Electrochemistry-Module-User_Manual, p.22-23 ### Why must the Q-1 EQCM cell be completely filled with electrolyte? *Applies to: Q-1* After assembly it is essential to **completely fill the cell up to the electrochemical probe insertion ports** . Any free air-liquid interface introduces significant baseline noise and spurious oscillations that can mask the real phenomena. Best practice: fill slowly to avoid trapping air bubbles, use slightly positive pressure to displace trapped air, consider a degassed solution, keep temperature stable, and check the level periodically during long experiments to compensate for evaporation. Source: openQCM_Electrochemistry-Module-User_Manual, p.27 ### How do I regenerate a coated gold crystal electrochemically? *Applies to: all instruments* A study on openQCM 10 MHz gold crystals found electrochemical cycling the least invasive regeneration method. After three cycles, biosensor response fell by about **7 %** , against 16 % for oxygen plasma and 25 % for Piranha. The study used a three-electrode cell (Au working electrode, Pt counter electrode, Ag/AgCl reference) and three alternative recipes: - 50 mM H_2SO_4: −400 to +1400 mV, 12 cycles at 100 mV/s - 50 mM HCl: −500 to +1500 mV, 10 cycles at 100 mV/s - 50 mM KOH: −100 to −1200 mV, 10 cycles at 50 mV/s All three variants caused little damage. The drawback is that only one crystal is cleaned at a time, and you need a potentiostat; the EQCM module can host the crystal. Every regeneration removes a little gold, so expect sensitivity to fall slowly over many cycles. Source: Wasilewski et al., *Biosensors* 2022, 12, 309, [doi:10.3390/bios12050309](https://doi.org/10.3390/bios12050309). Source: Wasilewski et al., Biosensors 2022, 12, 309, p.5, 10-13 ### What is in the NEXT EQCM box, and what do I need to supply myself? *Applies to: NEXT* **In the box** : quartz holder, PTFE reservoir, fixing ring, quartz cylinder, PTFE cover with fittings, two probe fitting adapters and a 2 mm green male banana plug for the working-electrode lead. **You supply** : - a **potentiostat** with working, reference and counter leads (the module has none built in); - your own **reference and counter electrodes** , which fit the two 6.2 mm cover ports; - an openQCM crystal, which becomes the working electrode; - degassed electrolyte, enough to fill the cell (~15 ml) up to the probe ports. The cell is used with the NEXT heatsink tilted to horizontal. An optional adjustable support for the front foot keeps it from tipping. Source: openQCM_NEXT-Electrochemistry-Module, p.7-9, 22, 25-27 ### My electrodes do not fit the EQCM cover ports. What can I do? *Applies to: NEXT, Q-1* The PTFE cover has two 6.2 mm primary ports for standard reference and counter electrodes. Two smaller auxiliary ports are for electrolyte exchange or continuous flow. The included fitting adapters take smaller probes. For other sizes or layouts you can: - order a **custom cover** from us (custom port sizes are available on request), or - make your own from the dimensional drawing of the cover in the user guide. Keep the cover in PTFE or another material compatible with your electrolyte, and make sure the cell can still be filled completely up to the probe ports. Source: openQCM_NEXT-Electrochemistry-Module, p.12, 22; openQCM_Electrochemistry-Module-User_Manual, p.24 ### What safety precautions apply when assembling the EQCM cell? *Applies to: NEXT, Q-1* - Wear **lab gloves** , and **safety glasses are mandatory** , when handling the quartz cylinder: it is glass and can break. - Work on a clean, stable, well-lit surface. - Place the crystal with plastic-tipped tweezers and check that it lies completely flat. A tilted crystal can crack when the reservoir is installed. - Never force a part. If you feel resistance, stop and recheck the alignment. - Tighten the fixing ring only to moderate resistance. - Disconnect the potentiostat and power before disassembly or cleaning. - Never use acetone or aggressive organic solvents on the parts. Source: openQCM_NEXT-Electrochemistry-Module, p.14-18, 20-21, 28-29 ### Can I run EQCM with a Wi2, or wire my own electrochemical cell to the QCM electronics? *Applies to: Q-1, NEXT, Wi2* For EQCM use the electrochemistry module on a **Q-1** or **NEXT** . The **Wi2 is not suitable** : its Pierce oscillator sustains the vibration itself, and a potential or current applied to a crystal electrode disturbs the oscillator and shifts its frequency. If you build your own cell for a Q-1 or NEXT, keep these rules in mind: - The crystal is driven on two lines: QCM IN carries the excitation to the crystal, QCM OUT brings back the signal after the crystal. In the standard electronics neither electrode is grounded. - Connect the potentiostat working electrode only to the electrode that faces the liquid, on the QCM OUT side. Check with a multimeter which contact pad it is; do not trust wire colours. - Keep all leads short and shielded. A wrong working-electrode connection is the first thing to check when a custom cell gives poor QCM or electrochemical signals. Source: openQCM support archive (19 threads) ### Noise rises or the resonance disappears when I connect my potentiostat. What is wrong? *Applies to: Q-1, NEXT* The crystal electrodes are part of the QCM measuring circuit and are not referenced to ground. Two situations cause trouble: - **Ground loop** : the potentiostat and the QCM share ground through the computer or the mains, and the noise rises. - **Direct path to ground** : if the working-electrode side sees ground, for example through a grounded counter electrode in a conductive solution, the resonance can disappear completely. What to do: - Run the potentiostat in floating mode, as users have done successfully. - To confirm a ground loop, run the laptop on its battery, unplugged from the mains, and compare. - Keep the QCM and electrochemistry cables short and route them apart. The openQCM electrochemistry module keeps the QCM and electrochemical circuits isolated, so both can measure at the same time. If your method requires a grounded working electrode, contact support before starting. Source: openQCM support archive (1 thread) ### My EQCM signal fluctuates by hundreds of hertz, or I need to seal my own electrodes in the cover. What should I do? *Applies to: Q-1, NEXT* Large fluctuations almost always mean the cell is **not completely filled** . Any air pocket or free liquid surface inside the cell moves and shows up in frequency and dissipation. Fill up to the electrode ports, slowly and with degassed electrolyte, and check the level during long runs, because evaporation re-creates a free surface. The cell holds much more liquid than a flow cell, so a slow drift during the first period after filling is normal. Allow time for thermal and mechanical relaxation before setting the reference. When you fit your own electrodes: - Adhesives bond poorly to PTFE. Conical gaskets, cable-gland style O-rings or thread-sealing tape around the electrode body seal better. Parafilm has added noise in practice. - For unusual electrode sizes, a custom cover can be made from the published drawings. - Clean PTFE parts with water, mild detergent or isopropanol, never acetone. Source: openQCM support archive (4 threads) ### What should I watch for when I follow electrodeposition or electropolymerisation with the QCM? *Applies to: Q-1, NEXT* - **Load** : deposits grow quickly. Keep the total frequency shift well below the saturation limit (see the FAQ on maximum mass). Soft or porous polymers damp the crystal much earlier than rigid metal films. Beyond the limit the resonance collapses and the software reports cut-off warnings. - **Uniformity** : the Sauerbrey equation assumes a uniform, rigid film. Rough, localised or edge-heavy deposits give only an approximate mass. Use dissipation and, on NEXT, several overtones to judge rigidity. - **Contacts** : keep electrolyte and deposits off the contact side of the crystal. - **Combined measurement** : the electrochemistry module keeps the QCM and electrochemical circuits isolated, so you can record both at once. Correlate the charge passed with the mass change to estimate deposition efficiency. - **Thickness** : for thick deposits, 5 MHz crystals give more dynamic range than 10 MHz crystals. Source: openQCM support archive (2 threads) ## Materials & chemistry ### Which materials are in contact with the fluid? *Applies to: all instruments* The wetted parts are: - **Quartz crystal** with a **gold** electrode - **Fluidic cell** : PMMA (Plexiglas) as standard, or **PTFE / Teflon** as a chemically inert custom option - **O-ring** : FKM (Viton) - **Tubing** : Tygon We can also supply custom cell materials for demanding chemistries — contact us with your solvent and concentration. Source: https://forum.openqcm.com/d/2-chemical-material-compatibility ### Can I use organic solvents, acids or surfactants (e.g. SDS)? *Applies to: all instruments* The standard **PMMA** cell swells and dissolves in many organic solvents (for example ethanol), so it should not be used with them. For acidic solutions or surfactants such as **SDS** , prefer a **PTFE** cell together with Viton O-rings and Tygon tubing. As a rule, do not use PMMA with acids. If you tell us your exact solvent and concentration we can recommend an inert configuration. Source: https://forum.openqcm.com/d/26-q-1-chemical-compatibility ### What are the thermal properties of the case, the cell and the O-rings? *Applies to: all instruments* The 3D-printed case is **Nylon** (strong & flexible plastic), dishwasher-safe and heatproof to **80 °C** ; higher temperatures may change the material properties. The window cell is **PMMA** (Plexiglas), glass transition ~105 °C (it softens above ~100 °C), with a thermal-expansion coefficient α_V ≈ (5–10)×10⁻⁵ K⁻¹. The chamber O-rings are **FKM (Viton)** . ### What is the best tubing for liquid applications, and which diameter? *Applies to: all instruments* We generally use **Tygon® 2375-C** high-purity tubing (Saint-Gobain), which resists acids, bases, ketones, salts and alcohols. Recommended dimensions are **OD = 3.2 mm, ID = 1.6 mm** . If you run a peristaltic pump, use a thinner tube in the pump head (e.g. Tygon ID = 0.51 mm) — a smaller bore reduces frequency fluctuations. ### What are the inlet and outlet hole diameters of the window cell? *Applies to: all instruments* The two CNC-milled holes are deliberately different sizes: - **Inlet** (larger): ID = 0.9 mm, OD = 1.8 mm - **Outlet** (smaller): ID = 0.6 mm, OD = 1.6 mm ### Which Wi2 materials touch the sample, and are there chemical compatibility limits? *Applies to: Wi2* The only sensor-module materials in contact with the sample are those of the measurement chamber: the **window cell** – standard material is **PMMA** acrylic glass (Plexiglas®) or **PTFE** (Teflon®) – and the **FKM Viton® O-ring** . It is strongly suggested **not** to use the PMMA window cell with organic solvents, because PMMA swells and dissolves in many organic solvents (such as ethanol) and has poor resistance to chemicals that hydrolyse its ester groups. Be very careful with aggressive chemical materials. Source: openQCM_Wi2-user_manual.pdf, p.14 ### Which materials of the openQCM TWIN come into contact with the sample? *Applies to: TWIN* None on the board: TWIN is an OEM board without a fluidic cell, so the materials in contact with the sample are those of the sensor holder you integrate. In all cases, pay close attention to aggressive chemical materials. Source: openQCM_TWIN_User_Manual.pdf, p.6 ### Which materials of the openQCM Holder come into contact with my sample? *Applies to: Holder* The Holder has no fluidic module: the board is FR-4 with gold pads, and only the crystal (Ti/Au electrodes on quartz) is exposed. When working with aggressive chemicals, check their compatibility with these materials and follow good engineering practice. Source: openQCM Holder.pdf, p.6 ### How do I clean a gold-electrode QCM sensor with the ammonium peroxide (TL1) mixture? *Applies to: all instruments* For gold sensors (QSX 301), the ammonium-peroxide method efficiently removes organic and biological material by oxidation. **Caution:** carry out the procedure under a fume hood with eye protection and gloves. 1. UV/ozone treat for 10 minutes. 2. Heat a **5:1:1 mixture of milliQ water, ammonia (25%) and hydrogen peroxide (30%)** to **75°C** (about 10 ml). 3. Immerse the sensor in the heated solution for **5 minutes** . 4. Rinse with milliQ water — keep the surfaces wet after immersion until well rinsed. 5. Dry with nitrogen gas, then UV/ozone treat again for 10 minutes. For platinum (QSX 314, protocol A-II) the same APM step is used, followed by a milliQ rinse, nitrogen drying, a 99% ethanol rinse and a final nitrogen dry (no UV/ozone steps). Source: cleaning_and_immobilization_protocols.pdf, p.4 ### How do I clean a silicon dioxide QCM sensor with SDS surfactant? *Applies to: all instruments* For SiO_2 sensors (QSX 303, 318, 328, 330), Sodium Dodecyl Sulfate (SDS) removes organic and biological material (proteins and lipids) by lowering interfacial tension. 1. UV/ozone treat for 10 minutes. 2. Prepare a **2% SDS solution in milliQ water** . 3. Immerse the sensor for **30 minutes at room temperature** . 4. Rinse with milliQ water — keep the surfaces wet after SDS immersion until well rinsed. 5. Dry with nitrogen gas, then UV/ozone treat again for 10 minutes. Source: cleaning_and_immobilization_protocols.pdf, p.5 ### How do I clean metal or metal-oxide QCM sensors with Hellmanex? *Applies to: all instruments* Hellmanex removes proteins and lipids and is somewhat more aggressive than SDS. **Note:** Hellmanex gives alkaline solutions that may etch glassware and quartz. 1. Immerse the sensor in **1% Hellmanex II** at room temperature for **30 minutes** (QSX 304 and 311 may be left 12 hours; for protocol C-II, QSX 322 30 min, QSX 319 3 hours, QSX 316 12 hours). 2. Rinse with milliQ water and dry with nitrogen gas. 3. Sonicate in 99% ethanol for 10 minutes, rinse with milliQ water, and dry with nitrogen gas. For C-I surfaces (stainless steel, titanium, tantalum, tantalum nitride) finish with a 10-minute UV/ozone treatment. Source: cleaning_and_immobilization_protocols.pdf, p.6 ### How do I clean a QCM sensor using only an alcohol (ethanol) treatment? *Applies to: all instruments* Alcohol treatment removes organic and biological material by dissolution and is used for surfaces such as aluminum oxide, cerium oxide (E-I), iron oxide (E-II) and hydroxyapatite (E-III). - **E-I / E-II:** sonicate in **99% ethanol for 15 minutes** , rinse with milliQ water, dry with nitrogen gas (E-I also adds a final 10-minute UV/ozone step). - **E-III (hydroxyapatite):** UV/ozone treat 10–20 min, immerse in 99% ethanol for 30 min, rinse with milliQ water, dry with nitrogen, then UV/ozone treat 10–20 min. Source: cleaning_and_immobilization_protocols.pdf, p.8 ### How can I spin-coat a thin polymer film onto a QCM sensor? *Applies to: all instruments* Spin-coating forms a thin, even polymer layer on any sensor surface; varying concentration and spin speed changes the thickness. **Caution:** the solvents are typically hazardous, so always work under a ventilated hood with eye protection and gloves. 1. UV/ozone treat the crystal for 10 minutes. 2. Prepare a polymer solution (e.g. **0.5% w/w** : PS in toluene; PMMA or PC in dichloromethane). 3. Place the crystal on the spin coater and apply 2–3 droplets of solution. 4. Spin at **2000 rpm for 20 seconds** . 5. Remove any polymer residue from the backside with a solvent-soaked cotton stick. 6. Evaporate the solvents by placing the crystals in an oven at ~80°C for 30 minutes. Source: cleaning_and_immobilization_protocols.pdf, p.11 ### How do I create a biotinylated-albumin linker layer on a gold QCM sensor for streptavidin/biotin coupling? *Applies to: all instruments* On a gold sensor (QSX 301) you can build a biotin/streptavidin linker surface: 1. **Clean:** immerse in a heated 5:1:1 APM mixture (milliQ water, 25% ammonia, 30% H_2O_2) at 75°C for 5 min, rinse in milliQ water (keep wet until rinsed), dry with N_2, UV/ozone treat 15 min, rinse and dry again. 2. **Apply biotinylated albumin:** dissolve to **10 µg/ml in de-gassed milliQ water** and rinse over the sensor; successful adsorption gives a frequency shift of about **-15 Hz** (normalized). 3. **Apply streptavidin/neutravidin:** dissolve to 10 µg/ml in de-gassed Tris buffer (10 mM Tris, 100 mM NaCl); a successful binding again gives about -15 Hz. Note that biotinylated-albumin layers may be less inert than phospholipid bilayers, so some non-specific binding can occur. Source: cleaning_and_immobilization_protocols.pdf, p.14-15 ### How do I form an NTA/Ni2+ supported lipid bilayer to immobilize His-tagged proteins, and can it be regenerated? *Applies to: all instruments* On a SiO_2 sensor (QSX 303) you can build an NTA/Ni-doped supported lipid bilayer for controlled His-tag protein capture: 1. Clean the sensor in 0.4% SDS for 2 h, rinse in milliQ water, dry with N_2, UV/ozone 15 min, rinse and dry again. 2. Prepare vesicles from 95 mol% POPC and 5 mol% DOGS-NTA, sonicate to clarity, and apply by injecting 40 µl of vesicle solution into 2 ml buffer; a successful bilayer gives a frequency shift of about **-26 Hz** and a dissipation shift close to zero. 3. Activate the NTA groups by rinsing a saturated **NiCl_2** solution (e.g. 2.5 mM) over the sensor for 5 minutes. The surface then captures His-tagged proteins via the Ni^2+ sites. After measurement, rinse with **EDTA or imidazole** for a couple of minutes to remove bound proteins and Ni^2+ ions and re-access the NTA surface. Source: cleaning_and_immobilization_protocols.pdf, p.12-13 ### How is Piranha solution used to clean a QCM gold electrode, and what are the cautions? *Applies to: all instruments* Piranha solution is prepared by mixing concentrated sulphuric acid and 30% hydrogen peroxide in a **7:3 ratio** . In the reported procedure each sensor was immersed in **10 ml of Piranha for 10 minutes** , then rinsed with demineralized water and ethanol and dried with nitrogen. **Caution:** Piranha is very toxic and requires safety procedures; mixing the components is strongly exothermic and self-heats strongly and can exceed 100 °C (so external heating is unnecessary). It is effective but the most invasive method — it erodes the gold, changes surface wettability, and reduces sensor lifetime and sensitivity over repeated cycles. Source: CLEANING-biosensors-12-00309-v2.pdf, p.4 and p.12 ### How do I prepare a self-assembled monolayer (SAM) on a gold QCM sensor? *Applies to: all instruments* A carboxylic-acid SAM can be formed on a gold sensor as follows: 1. Prepare a **1 mmol/l carboxylic-acid SAM solution** in ethanol, then dilute it 10-fold with ethanol. 2. Immerse the gold substrate in the solution at room temperature and leave it **overnight** . 3. Wash the substrate several times, sequentially, with ethanol and then purified water. The resulting SAM provides reactive groups that can subsequently be activated (e.g. with EDC/NHS) for covalent immobilization of receptor proteins. Source: se0c01641_si_001.pdf, p.5 ### Which parts of openQCM NEXT touch the sample? *Applies to: NEXT* Only the measuring chamber touches the sample. That means the crystal (quartz with Ti/Au electrodes), the **PTFE (Teflon) fluidic core** and an **FKM (Viton) O-ring** . The fluidic channels are machined directly into the PTFE core, which also helps bring the liquid to the set temperature before it reaches the crystal. PTFE and FKM resist a wide range of chemicals, but check aggressive media with us before use. The optional optical module adds a quartz window held by a mechanical joint, with no adhesive in contact with the sample. Source: openQCM NEXT user guide, p.7, 13, 19 ### Which pH range and solvents can the fluidic cell take, and how do I recognise chemical damage? *Applies to: Q-1, Wi2, NEXT* Only the crystal, the O-ring and the cell window or core touch the sample. The material list is in the FAQ on wetted parts; these are the practical limits support sees most often. - **PMMA window (Q-1, Wi2):** fine for water, buffers and dilute solutions, for example a few percent of methanol in buffer. Not for organic solvents: ethanol swells it and acetone causes stress cracks. Use the PTFE cover instead. - **PTFE core or cover (standard on NEXT):** resists almost all chemicals. - **FKM (Viton) O-rings:** resist many acids and hydrocarbons, but penetrating solvents such as DMSO or ketones can swell them. Swelling shows up as a steady baseline drift. More resistant O-rings of the same size, such as FFKM, are an option. - **Extreme pH** (for example pH 2 or 13) has not been tested. Use PTFE parts, test on a non-critical setup first and inspect the O-ring afterwards. Signs of damage are a cloudy or cracked window, persistent drift, or liquid under the crystal. Keep liquid away from the electronics and nylon parts. The manuals advise against use near flammable liquids or fumes, so assess flammable solvents under your laboratory safety rules. Source: openQCM support archive (41 threads) ### Can I sterilise or autoclave the Q-1/Wi2 sensor module? *Applies to: Q-1, Wi2* Do not autoclave it. The printed nylon (PA2200) parts are rated to about 80 °C and change their properties above that, so steam sterilisation would damage the module. For disinfection: - The wetted parts are only the window, the O-ring and the crystal. A PMMA window must not see ethanol or other solvents, because it swells or cracks. A PTFE window or cover tolerates a much wider range of disinfectants. - The PTFE covers still have a nylon frame, so check that your disinfectant is compatible with nylon too. - Do not let liquid reach the proximity board or the pogo pins. If it does, follow the sensor-module cleaning procedure (isopropyl alcohol in an ultrasonic bath, then complete drying). For cell-culture work, clean and sterilise the crystal separately, and handle the assembled module with aseptic technique. Source: openQCM support archive (3 threads) ### Are crystals single-use? How many times can I clean and reuse one? *Applies to: all instruments* Crystals are consumables, but a crystal whose electrodes stay intact can usually be cleaned and reused several times. How many times depends on your layer and on the cleaning method, because every cycle removes a little electrode material. Choose the mildest method that removes your layer: 1. **Gentle routine:** about 30 min in an ultrasonic bath of pure isopropyl alcohol, rinse, dry with nitrogen. Often enough for new crystals and light residues. New crystals carry no photoresist, because the electrodes are deposited through a shadow mask. 2. **Standard for gold:** UV/ozone plus the ammonia–peroxide mixture described in the TL1 cleaning FAQ. 3. **Least invasive regeneration:** electrochemical cycling, with about 7 % loss of response after three cycles in a published study on openQCM crystals. 4. **Piranha:** effective but hazardous. It erodes the gold and can destroy the thin wrap-around contact, leaving the crystal without signal. Replace a crystal when the peak becomes lower or broader, the baseline is unstable, the sensitivity drops or no peak is found. For quantitative series, use crystals with a similar cleaning history. Source: openQCM support archive (22 threads) ### Which side of the crystal should I coat, and can I deposit my own film? *Applies to: all instruments* Coat only the top side, the one with the large 12 mm electrode. The back carries both electrical contacts, which must stay clean and dry. A deposit there, especially a conductive one, can short the electrodes or spoil the pogo-pin contact. Coating both faces also makes the mass calculation ambiguous. You can sputter, evaporate or spin-coat metals, oxides, polymers or carbon onto the front electrode yourself: - Record the frequency before and after deposition. For a thin, rigid film the shift gives its mass (Sauerbrey), and the coated frequency becomes the new baseline. - Keep conductive material from creeping around the edge onto the back contacts. - A thicker edge bead matters little: sensitivity is highest at the centre and close to zero at the electrode edge. - Keep the total load well below the saturation limit. Every coating uses part of it. - For polymer films used in water, a surface pretreatment such as oxygen plasma or silanisation improves long-term adhesion. Source: openQCM support archive (11 threads) ### Which electrode materials are available, and which should I choose? *Applies to: all instruments* The standard openQCM crystals have **gold on a titanium adhesion layer** (50 nm Ti and 200 nm Au on the AT5 datasheet). There is no dielectric layer, and the titanium is not exposed to the sample. - **Gold** is the default. It is chemically stable, binds thiols and is supported by many published protocols for antibodies, DNA and SAMs. It is soft, so avoid abrasive cleaning. - **SiO₂** gives a silica-like surface for adsorption on oxides or glass, lipid bilayers and silanisation. - **Other metals** , such as platinum, titanium or stainless steel, have been supplied for specific projects or can be requested from the crystal manufacturer as custom batches, usually with a minimum order quantity. Check the store or ask support. openQCM does not supply pre-functionalised crystals; functionalisation is done by the user. Third-party coated crystals work if they are 14 mm with wrapped electrodes. Whether a coating suits your analyte is best checked with a short preliminary experiment. Source: openQCM support archive (44 threads) ### What should I expect from SiO₂-coated crystals in water? *Applies to: all instruments* SiO₂ sensors use the same 14 mm wrapped format as the gold ones, with a thin silica film (about 50 nm) over the gold electrode. They are mainly used for silica-like surfaces, lipid bilayers, silanisation and water-adsorption studies. Points from support experience: - **Slow baseline change in water.** Silica takes up water slowly, so dissipation can rise gradually and frequency can fall over a few hours even on a stable instrument. Record a clean SiO₂ crystal under the same conditions as a reference, and compare with a gold crystal to rule out a hardware fault. - **Delicate film.** The oxide can delaminate, even with mild detergents. Treat these sensors as essentially single-use; harsh cleaning is not recommended. - A short UV/ozone treatment before use removes organic contamination. For long aqueous experiments that do not need silica chemistry, gold is the more stable choice. Source: openQCM support archive (10 threads) ### My SAM or antibody functionalisation gives no frequency shift. What should I check? *Applies to: all instruments* Gold is a good substrate for thiol SAMs and antibody immobilisation, so the cause is usually surface preparation or the measurement protocol. - **Cleaning:** contaminated gold blocks SAM formation. Clean new crystals too, starting with an isopropyl alcohol ultrasonic bath and moving to a stronger method if needed. - **Compare like with like:** a frequency measured in air before and in liquid after cannot be compared. Take readings in the same liquid and at the same temperature, ideally while reagents flow over the mounted crystal. - **Check each step:** a modified surface is not always visible. Verify it with an optical microscope or another technique. - **Look at dissipation:** on the Q-1 or NEXT, ΔD shows whether a soft, hydrated layer formed even when Δf is small. Follow published protocols for your chemistry. The QCM immunosensor literature is extensive, and papers that used openQCM instruments are listed on the website. Source: openQCM support archive (4 threads) ### Can a QCM detect a specific gas, such as NOx, and give the result in ppm? *Applies to: all instruments* A bare QCM is not selective: it responds to any mass change at its surface. To detect a specific gas, functionalise the electrode with a coating or receptor that absorbs or reacts with it. Moisture is a partial exception, because many surfaces adsorb water readily, so humidity is also a common interferent to control. Very low amounts can be detected, since even a molecular layer is measurable, but converting frequency to ppm requires a calibration with known gas concentrations for your coating and conditions. The software is open source, so such a conversion can be added once you have the calibration curve. Dissipation (Q-1, NEXT) helps separate simple adsorption from swelling of the coating. For moisture detection, frequency alone is often sufficient, and the Wi2 is enough. Source: openQCM support archive (2 threads) ## Software & firmware ### How do I change the frequency sweep range / measurement window? *Applies to: Q-1* Edit the `constants.py` file in the Q-1 Python software, located at `...\openQCM_Q-1_py_v2.1\OPENQCM\openQCM\core\constants.py` Adjust the left/right offsets around the peak for the fundamental (and overtones): ``` # 10 MHz L10_fundamental = 7500 # widen the lower side of the sweep R10_fundamental = 2500 # widen the upper side ``` `L10_fundamental` is the frequency span to the left of the detected peak. For a large expected shift (e.g. ~44 kHz for glycerol) increase these values accordingly. **Note:** in the pre-built `.exe` version these source files are not exposed, so this edit is only possible with the Python distribution. Source: https://forum.openqcm.com/d/19-solved-adjusting-startstop-frequency-in-the-software ### How do I use 6 MHz crystals with the Q-1 software? *Applies to: Q-1* It is possible, but you must edit several source files: `constants.py`, `Calibration.py` and `switcher.py`. In `constants.py` add a 6 MHz block of sweep parameters, for example: ``` # 6 MHz (custom) L6_fundamental = 5500 R6_fundamental = 2500 SG_window_size5_fundamental = 9 # Savitzky-Golay window Spline_factor5_fundamental = 0.05 # spline smoothing # ...repeat for the 3rd / 5th / 7th overtones ``` **Known quirk:** some users find that the start/stop frequency and data-window size are still read from the `L10/R10` variables even at 6 MHz, so you may need to adjust those too. Edit only the Python distribution (not the `.exe`). Source: https://forum.openqcm.com/d/29-discussion-points-for-q-1-software ### Can I read crystals above 8 MHz? Can I change the baudrate? *Applies to: all instruments* On the original Arduino-micro openQCM, the `FreqCount` library is accurate up to ~8 MHz; higher frequencies (e.g. 10 MHz) are recovered with an **undersampling** correction, so the measured shift still matches the true value. The **Wi2 (Teensy 3.2)** handles frequencies above 8 MHz natively, so a 9 MHz crystal works without that limitation. The baudrate is set to 115200 for throughput; lowering it is possible but not recommended. Source: https://forum.openqcm.com/d/38-programming-alternate-frequencies ### The software slows down or freezes after running for a while. What can I do? *Applies to: Q-1* This is most often a **Windows Python-environment issue** rather than a hardware fault. The simplest fix is to use the **standalone executable** build of the Q-1 software (packaged with PyInstaller): unzip and run `app.exe`. The software has also been run successfully for hours on a **Raspberry Pi (Linux)** . If it persists, share the output of `conda list` so we can check your environment. Source: https://forum.openqcm.com/d/30-software-slowdown-after-long-runtime ### “Cut-off frequencies not found” warning, with implausible temperature/dissipation values. How do I fix it? *Applies to: all instruments* This warning means the half-power bandwidth (lower/upper cut-off) could not be located, so the readings shown in that state are unreliable. Try **widening the sweep window** in `constants.py` so the full resonance is captured, check the **sensor mounting and pogo-pin contact** , and clean the sensor. A peak that drifts out of the window, or a partially contacted crystal, is the usual root cause. Source: https://forum.openqcm.com/d/36-program-status-warning-cut-off-frequencies-not-found-error ### The Arduino COM port is not recognised, or I cannot upload the firmware. *Applies to: all instruments* First, install/update the Arduino driver and confirm the board is recognised. To upload the openQCM sketch you also need Paul Stoffregen’s [FreqCount](https://www.pjrc.com/teensy/td_libs_FreqCount.html) library — download it from [GitHub](https://github.com/PaulStoffregen/FreqCount/archive/master.zip) and add it via the Arduino IDE ( *Installing Additional Arduino Libraries* ). ### Is the openQCM software cross-platform? *Applies to: all instruments* Yes. The application runs on **Windows, macOS and Linux** . The firmware and software are open-source — see the [software page](https://openqcm.com/software/) for the installation guide and downloads. ### What is the difference between Single Measurement and Multiscan Measurement modes? *Applies to: NEXT* In the software's Operation Mode setting, **Single Measurement** monitors frequency and dissipation in real time on a single chosen frequency of the quartz resonator spectrum. **Multiscan Measurement** monitors frequency and dissipation in real time on the fundamental and all available overtone harmonics, swept one after another in every multiscan cycle, about 1.4 s per overtone. Before measuring you must run **Calibration** , which records the resonator calibration signal for resonance peak detection (selecting a 10 MHz or 5 MHz fundamental). Source: openQCM NEXT user guide, p.28 ### How do I set a reference and choose the datalog sampling time? *Applies to: NEXT* Press **Set Reference** to fix the current frequency and dissipation as the reference for measuring variations (works in single and multiscan modes); **Reset Reference** returns them to actual values. In Multiscan Measurement, choose the **Datalog Sampling Time** from the drop-down menu; the default is the hardware minimum of **7 seconds** . Frequency is shown in Hz and dissipation in ppm. Source: openQCM NEXT user guide, p.29-30 ### What are the default PID parameters and set temperature in the NEXT software? *Applies to: NEXT* Enable thermal control with **Temperature Ctrl ON** . The default **Temperature Set** is 25 °C (working range 25–45 °C). The TEC PID defaults are: P Share 1000 mA/K, I Share 200 mA/(K·sec), and D Share 100 (mA·s)/K, each adjustable from 0 to 100000 via **PID Set** . If the controller enters an error state, use **TEC Controller Reset** (disabled by default) to reset it. Source: openQCM NEXT user guide, p.29 ### How do I install the openQCM Q-1 software? *Applies to: Q-1* Download the Q-1 Python application v2.1 from [openqcm.com](https://openqcm.com/downloads/q-1/software/openqcm-q-1-software-2.1-source.zip), then: 1. Download and install **Anaconda3 for Python 3.7** (Anaconda3-5.3.0). Selecting "Just Me" avoids needing an elevated console. 2. Open the Anaconda3 prompt (Windows) or terminal (macOS) and run: `conda install pyqtgraph pyserial`, `python -m pip install --upgrade pip`, `python -m pip install --upgrade h5py`, and `pip install progressbar`. The software runs on Windows, macOS and Linux. Source: openQCM_Q-1-user_manual, p.14-15 ### How do I install and run the Q-1 software on Linux? *Applies to: Q-1* On Linux there are a few extra steps: 1. Change ownership of the Anaconda3 folder: `sudo chown -R username:username /home/username/anaconda3` (replace *username* with your own). 2. Open the Anaconda3 terminal and run `conda install pyqtgraph pyserial`, `pip install --upgrade pip --user`, and `pip install progressbar --user`. 3. Set serial-port permissions: `sudo usermod -a -G uucp username` and `sudo usermod -a -G dialout username`. 4. Log out and log back in. Source: openQCM_Q-1-user_manual, p.16 ### How do I start the openQCM Q-1 GUI? *Applies to: Q-1* You can launch the application from the Anaconda3 prompt: launch the prompt, browse to the software main directory `...\openQCM_Q-1_py_v2.1\OPENQCM\`, and run `python -m openQCM`. Alternatively you can run the `app.py` file directly by associating it with the `python.exe` executable inside your Anaconda3 directory and double-clicking it. Source: openQCM_Q-1-user_manual, p.17 ### What files does Q-1 calibration create, and can I delete them? *Applies to: Q-1* After a successful calibration the system saves `Calibration_5MHz.txt` or `Calibration_10MHz.txt` (depending on the @5 MHz or @10 MHz sensor) plus `PeakFrequencies.txt`, which lists the detected peak frequencies. **Do not remove or modify these system files** , otherwise the software may stop working. A backup of the initial-setup files is kept in the `backup` folder. Note that no files are saved if calibration fails. Source: openQCM_Q-1-user_manual, p.25-26 ### Where are my Q-1 measurement data saved and in what format? *Applies to: Q-1* Frequency, dissipation and temperature data are stored automatically each time a new acquisition starts, in `...\openQCM_Q1_py_v2.1\OPENQCM\logged_data`. The file is a `.csv` named `[Timestamp]_[overtone name].csv` with five columns: Date, Time, Relative_time (seconds from start), Resonance_Frequency and Dissipation. If "Txt Export Sweep File" is enabled, raw sweep files are also saved as `sweep_[overtone name]_[sweep number].txt` containing frequency, amplitude (dB) and phase (deg). Source: openQCM_Q-1-user_manual, p.30-31 ### How is the Wi2 connected and powered, and what does the software do? *Applies to: Wi2* The Wi2 connects to a PC via a **USB** connection and is powered at **5 VDC** through the USB port (cable included); the modular main body connects to the external fluidic measuring cell using a standard USB 3.0 connector. The GUI monitors frequency variations in real time and uniquely identifies each device by its **COM port** , so you can plug in multiple devices simultaneously. Experimental data can be saved to a file for post-processing, and the interface displays live frequency and temperature charts. Source: openQCM_Wi2-user_manual.pdf, p.5, p.11, p.13 ### How do I install the Wi2 software on macOS? *Applies to: Wi2* On macOS, install the software as follows: 1. Download and install the latest **Java Runtime Environment version 8u*** for Mac OS X x64. 2. Download and unzip `openQCM_Wi2_v1-macOS.zip`. 3. Open the `.../RXTX-lib-natives` folder, then copy `RXTXcomm.jar` and `librxtxSerial.jnilib` into `/Library/Java/Extensions`. 4. In the terminal, run (replacing *username* with your profile name): `export DYLD_LIBRARY_PATH=/Library/Java/Extensions`, `sudo mkdir /var/lock`, `sudo dscl . -append /groups/_uucp GroupMembership username`, `sudo chgrp uucp /var/lock`, `sudo chmod 775 /var/lock`. 5. Browse to the openQCM Wi2 directory and run `openQCM_Wi2_v1.jar`. On Windows, simply unzip `openQCM_Wi2_v1-app.zip` and launch `openQCM_Wi2_v1.exe` (a stand-alone driver installer is provided). Source: openQCM_Wi2-user_manual.pdf, p.12 ### How does the sample firmware compute frequency and what is the measurement timing? *Applies to: TWIN* The example firmware counts rising edges of each crystal signal over a **2 ms gate interval** (`GATE_INTERVAL 2000` µs) and accumulates **500 cycles** (`GATE_ACCUM 500`), giving an exact **1-second** measurement window so the accumulated count equals the frequency in Hz. A unity multiplication factor (`MULT_FACTOR 1`) gives a direct Hz readout. This accumulation/averaging improves stability and reduces noise, and 16-bit counter overflow is handled automatically through modulo arithmetic. Source: openQCM_TWIN_User_Manual.pdf, p.22, 24, 25 ### What is the serial data format output by the openQCM TWIN firmware? *Applies to: TWIN* The firmware streams data over USB serial at **115200 baud** as a formatted string `F[ref_freq],[sensor_freq],[diff]`. For example, `F10000000,10000123,123` represents a 123 Hz shift of the sensor relative to the reference frequency. Temperature readings are also published, prefixed with `T` for the MTD415T (queried with the `Te?` command) and `C` for the onboard MCP9808 sensor. Source: openQCM_TWIN_User_Manual.pdf, p.26, 27, 30 ### What software, libraries, and tools do I need to build and customize the firmware? *Applies to: TWIN* The openQCM TWIN is an OEM platform supplied with complete example firmware (full source in Appendix A) intended as a foundation for custom development. It targets the **Teensy 4.0** and is built with the **Arduino IDE 2.0** (CLI version 0.32.2). The firmware depends on three libraries: - `IntervalTimer` (Teensy core library) - `Adafruit_MCP9808` (temperature sensor library) - `FreqCountMany` by Paul Stoffregen (PJRC) Source: openQCM_TWIN_User_Manual.pdf, p.22, 28, 31 ### What microcontroller does the SpaceBug use and in what languages can it be programmed? *Applies to: SpaceBug* At the heart of the SpaceBug is the **Seeeduino XIAO Arduino SAMD21 Cortex® M0+** (SAMD21G18), a 32-bit 48 MHz microcontroller with **256 KB Flash and 32 KB SRAM** . It controls the device's subsystems, manages power, and handles communication. The device can be programmed in **C++ (Arduino)** or **MicroPython** . It ships with pre-installed firmware that includes a library for the RV-3028 Real-Time Clock, so users do not need to write their own RTC integration code. Source: openQCM SpaceBug.pdf, p.10, 11, 17 ### How do I set up the Arduino IDE to program the SpaceBug? *Applies to: SpaceBug* 1. Download and install the Arduino IDE from [arduino.cc](https://arduino.cc) for your operating system. 2. In `File > Preferences`, add this Board Manager URL: `https://files.seeedstudio.com/arduino/package_seeeduino_boards_index.json` 3. Open `Tools > Board > Boards Manager`, search for *Seeeduino XIAO* , and install the "Seeed SAMD Boards" package. 4. Select **Seeeduino XIAO** under `Tools > Board`, then choose the correct port under `Tools > Port`. 5. Install required libraries via `Sketch > Include Library > Manage Libraries`: `Melopero_RV3028`, plus `SPI` and `SD`. To verify the setup, upload the `01.Basics > Blink` example; the onboard LED should blink. Source: openQCM SpaceBug.pdf, p.18, 19 ### I am flashing the firmware myself. Which CPU speed should I choose? *Applies to: Q-1, Wi2* The mounting manuals ask you to flash the firmware from the Arduino IDE with the Teensyduino add-on (PJRC) and to set `Tools › CPU Speed` to **150 MHz** . The microcontroller can run much faster, but the lower clock produces less heat inside the enclosure. That matters because the crystal and the temperature sensor are only a few millimetres away, and self-heating would show up as frequency drift and a biased temperature reading. After upload, check that the blue LED on the sensor module lights. If it does not, check the USB connection, the upload log, the LED soldering and the USB port power. Source: openQCM_Q-1-mounting_manual, p.41-42; openQCM_Wi2-mounting_manual, p.41-42 ### What is the measurement workflow in the NEXT software? *Applies to: NEXT* 1. **Connect** and select the COM port. 2. **Calibrate** after mounting a crystal: choose 5 or 10 MHz. The software scans amplitude and phase from 1 to 51 MHz and locates the resonance peaks. 3. **Set the temperature** (Temperature Ctrl ON; default 25 °C) and let the cell stabilise. 4. **Measure** in *Single* mode (one harmonic) or *Multiscan* mode (all available overtones, about 1.4 s each). 5. **Set Reference** once the baseline is flat, so the plots show Δf (Hz) and ΔD (ppm). 6. **Data** are saved as CSV. The beta *Log data view* replots the current session. The *Raw data view* shows each sweep with the points used for frequency and dissipation. Source: openQCM NEXT user guide, p.27-31 ### What should I know when integrating the TWIN serial output into my own software? *Applies to: TWIN* - USB serial at 115200 baud. The `F` line (`F,,`) arrives once per second, from a 2 ms gate accumulated 500 times. `diff` is sensor minus reference and is signed. - `T` lines (MTD415T reply to `Te?`) and `C` lines (onboard MCP9808) come from separate reads, not synchronised with `F`. Pair them by arrival time. - Anything else you type on the port goes to the MTD415T, and its reply is echoed back. This is how you talk to the controller. - The TTL difference output carries only the **magnitude** of the difference, and it keeps its last value when the difference is zero. Use the `F` line when the sign matters. - Treat the Thorlabs MTD415T datasheet as part of the system documentation. Source: openQCM_TWIN_User_Manual, p.24-32 ### How can I reduce the number of data points in long or overnight experiments? *Applies to: NEXT, Q-1, Wi2* Each instrument logs at its own measurement rate: about once per second on the Wi2, once per sweep of the selected harmonic on the Q-1, and once per multiscan cycle on the NEXT (about 1.4 s per overtone). - **NEXT** : choose a longer *Datalog sampling time* , for example 10, 30 or 60 s. In some versions this control works only in multiscan mode; to log a single harmonic slowly, run multiscan with the other overtones switched off. - **All instruments** : down-sample the CSV file afterwards by averaging over your chosen interval (for example 5 or 30 minutes), which also reduces noise. - **Q-1 and Wi2** : the open-source code can be changed to log less often, and support has provided custom versions that average over a selectable interval. If very long runs show irregular sampling times or frozen values, check that power saving or another process on the PC is not slowing acquisition. Source: openQCM support archive (6 threads) ### Does the software convert frequency into mass or thickness, or fit viscoelastic models? *Applies to: all instruments* No. The software acquires, displays and logs frequency, temperature and (Q-1, NEXT) dissipation. It applies no Sauerbrey or viscoelastic model, because the right model depends on the sample and the medium. - **Rigid films** : apply the Sauerbrey equation to the exported data. Over the 0.196 cm² active area of current crystals, 1 Hz on the fundamental corresponds to about 3.5 ng at 5 MHz and about 0.9 ng at 10 MHz. Thickness is the areal mass divided by the film density. - **Soft or hydrated layers** : viscoelastic models (for example Voigt) need frequency and dissipation at several overtones, as logged by the NEXT in multiscan mode; a single harmonic (standard Q-1 use) is not enough. Load the CSV into your own scripts or into open-source or commercial modelling tools. - openQCM dissipation is an instrumental value from the peak width, so check its scaling against a reference, such as a Newtonian liquid, before absolute fitting. Because the code is open, a live mass or thickness display can be added; support has made such versions for deposition monitoring. Source: openQCM support archive (32 threads) ### Are dissipation values comparable between different software versions? *Applies to: Q-1, NEXT* Not directly. The way dissipation is computed has changed between releases of the Q-1 and NEXT software. For example, early versions took the peak width at a fixed fraction (70.7 %) of the peak amplitude, while later versions take it at a fixed, calibrated level below each harmonic's peak, which gives repeatable results on all overtones. The same raw data can therefore give different absolute dissipation values in different versions, with no simple conversion factor. Frequency is not affected, and dissipation changes within one experiment follow the same trends. Good practice: - record the software version in your lab book and publications; - analyse a whole series with the same version; - do not mix dissipation data from different versions in one quantitative comparison. Source: openQCM support archive (1 thread) ### Do I need to recalibrate after coating the crystal or adding liquid? Can I reuse a calibration? *Applies to: Q-1, NEXT* Calibration (peak detection) sweeps the crystal over about 1–50 MHz and finds its fundamental and overtone peaks; measurements then sweep a narrow window around each. Repeat it every time you change crystal, ideally with the clean crystal in air. A successful calibration shows 5 peaks for a 5 MHz crystal and 3 for a 10 MHz crystal. - After that, measure without recalibrating, even after adding liquid or a thin film: the window follows normal shifts. For multilayer work, press *Set Reference* after each stable step. - Recalibrate only if a large load has moved the resonance out of the window. On a heavily coated crystal recalibration can fail, because the higher overtones are too damped. - **Switching crystals** (Q-1): after calibrating, copy `PeakFrequencies.txt` and `Calibration_5MHz.txt` or `Calibration_10MHz.txt` into a folder named after that crystal. When you remount it in the same orientation, copy them back and start measuring. Its resonance must still lie inside the window. Keep a backup of the original files. Source: openQCM support archive (13 threads) ### Can I read data from an openQCM instrument with my own software (LabVIEW, Python, Raspberry Pi)? *Applies to: Q-1, NEXT, Wi2* Yes. Firmware and software are open source, and every instrument talks to the PC over a USB serial (COM) port. - **Q-1 and NEXT** : the PC sends the sweep parameters (start frequency, stop frequency, step) and the firmware returns amplitude and phase points plus temperature. All processing (baseline correction, smoothing, peak detection, width) runs on the PC. The serial classes are in the `processors` folder of the Python software. - **Wi2 and oscillator boards** : the firmware streams counted frequency and temperature lines that are easy to parse. Users have built interfaces in LabVIEW, MATLAB, C++ and Python, also on a Raspberry Pi. With your own Q-1/NEXT code you must handle peak finding, window centring and baseline correction; support has a basic LabVIEW example. Simpler routes: read the CSV that the standard software writes in real time, or extend the Python software, for example by sending the latest results from its data queues to a local TCP socket in a separate thread, or by triggering a pump when the baseline is stable. Source: openQCM support archive (21 threads) ### What computer do I need to run the openQCM software? *Applies to: all instruments* Modest resources are enough: a standard laptop or desktop running Windows (64-bit for the standalone executable), macOS or Linux, with about 8 GB of RAM and one free USB port per instrument. The Q-1 and NEXT software draws real-time charts of each sweep, so a reasonably recent processor helps, especially with several instruments. No internet connection is needed to measure: the software can be copied to an offline lab PC, as long as the USB serial driver is available. No anti-vibration table is needed either. For long runs: - disable sleep, hibernation and USB power saving, and run laptops on mains power; - avoid heavy background tasks and automatic restarts for updates; - keep enough free disk space. Irregular sampling intervals in the data file usually mean the PC is slowing acquisition. After an operating-system upgrade, test the software before a critical experiment. Source: openQCM support archive (11 threads) ### Can I use crystals with a fundamental other than 5 or 10 MHz? *Applies to: Q-1, NEXT, Wi2* - **Q-1 and NEXT** (network analyser): the standard software has 5 and 10 MHz presets, and calibration looks for the peaks expected for them. Another fundamental within the 1–50 MHz range shows up in the calibration sweep but is not tracked. Measuring it needs changes to the open-source Python code (peak search and sweep settings in the calibration and constants files); support has prepared custom versions on request. Any custom sweep must be wider than the resonance bandwidth, or dissipation will be wrong. - **Wi2 and oscillator boards** : the oscillator locks onto the crystal's fundamental by itself, so other fundamentals generally work without software changes. Check with support for the frequency you need. Whatever the frequency, the crystal must be a 14 mm blank with wrapped electrodes. A crystal with a contact on each face does not fit the standard modules. Source: openQCM support archive (10 threads) ### How do I open my data files in Excel, and what do the NEXT and Wi2 files contain? *Applies to: Q-1, NEXT, Wi2* Data are saved automatically during the measurement as CSV files in the `logged_data` folder of the software (with the Q-1 executable, `app/logged_data`). Stopping clears the plots, not the files. - **Q-1** : one file per run and harmonic with date, time, relative time (s), temperature, frequency and dissipation; optional raw sweep files (frequency, amplitude in dB, phase) via *Txt Export Sweep File* . - **NEXT** : frequency, dissipation (ppm) and temperature for each overtone. Raw sweeps appear in the Raw data view but are not logged routinely. - **Wi2** : a text file of frequency and temperature. In Excel use *Data › From Text/CSV* with a comma delimiter, and check the columns are numbers, not text. Logged values are absolute: subtract a baseline row to get shifts. A chart exported by right-click stores time as Unix epoch; use the logged file instead. Do not open the live file during acquisition; copy it. Dissipation cannot be recomputed later from logged values, so enable sweep export if you need the raw curves. Source: openQCM support archive (37 threads) ### Do I need Python to run the Q-1 or NEXT software, and how do I update it? *Applies to: Q-1, NEXT* Not on Windows. Each instrument has a free standalone Windows application with Python built in. Download it from the product page, extract the whole archive (running it from inside the zip makes the window close at once), keep the folder structure and start the program or its shortcut. The first start can take a while. The application needs its companion folders and calibration files, so do not move the executable; point a shortcut to it instead. **Updating** : no uninstall is needed. Extract the new version into its own folder; several versions can coexist. The Python source package is for macOS and Linux, or for anyone who wants to modify the code. Run it in the Anaconda environment described in the installation guide for that version and start it from a terminal (`python app.py` or `python -m openQCM`, depending on the package). Changes to the source do not affect the executable. Both packages offer the same measurement functions. Source: openQCM support archive (26 threads) ### Running the Python source gives errors such as 'QtGui has no attribute QMainWindow' or empty plots. How do I fix it? *Applies to: Q-1, NEXT* These errors come from library versions newer than those the code was written for, mainly pyqtgraph and PyQt5. On Windows the simplest fix is the standalone executable. To run the source: 1. Create a dedicated Anaconda environment with the Python and package versions given in the openQCM installation guide for your software version. pyqtgraph 0.11.0 is the critical one: 0.13.x and very recent Python releases cause missing Qt classes, empty real-time plots, "QRectF/boundingRect" type errors at calibration or progress-bar type errors. Do not accept the latest default packages (for example a plain conda-forge setup). 2. Install the packages listed in the guide (pyserial, progressbar and others) inside the activated environment and check with `conda list`. 3. Open a terminal in the correct folder and start the program there, so you can read the messages. "No module named openQCM" means a wrong folder; `python - m` with a space is a typo. Avoid patching imports by hand, and use the latest source package, which fixes a path-separator problem on Linux and macOS. Support can send the environment guide. Source: openQCM support archive (33 threads) ### How do I run the software on macOS, Linux or a Raspberry Pi? *Applies to: Q-1, NEXT, Wi2* - **macOS and Linux** : run the Python source (the executable is Windows-only) in a dedicated conda environment. Missing-file errors such as `PeakFrequencies.txt` mean the program was started from the wrong folder, lacks permissions, or is an old version with a Windows-only path separator. - **Serial access on Linux** : add your user to the `dialout` (and `uucp`) groups, then log out and in. - **Raspberry Pi (ARM64)** : use an aarch64 installer (for example Miniforge), but pin the package versions from the guide. If Qt cannot load the "wayland" plugin or the plots stay empty, start with `QT_QPA_PLATFORM=xcb` (and set `DISPLAY=:0` if it is empty). The Wi2 software runs well; the sweep processing of the Q-1 and NEXT is heavier and may lag on small boards. - **Virtual machines** : COM-port pass-through is often unreliable; prefer a native installation. - The old **Java** Wi2 software no longer works on recent macOS versions; use the current Python Wi2 software. Source: openQCM support archive (18 threads) ### Do the firmware and software versions need to match? Which Teensy does my device use? *Applies to: NEXT, Q-1, Wi2* Yes. Each instrument has its own software, and the firmware on its Teensy microcontroller must belong to the same instrument and generation. If the program connects but shows no data, freezes, or gives implausible frequencies or calibration errors, suspect a mismatch. - **NEXT** (Teensy 4.0): some software releases need a firmware update; the software warns you. - **Q-1** : older units use a Teensy 3.6, current units a Teensy 4.0; both run the current Q-1 software with their matching firmware. - **Wi2 and Teensy shield** : older units use a Teensy 3.2, current units a Teensy 4.0. Use a software version that supports your board; older software can freeze or show wrong frequencies with a Teensy 4.0. To check the hardware without the openQCM software, open a serial monitor (Arduino IDE with Teensyduino, 115200 baud): Wi2 and Teensy-shield boards stream data lines as soon as they are powered. A different output format means the wrong firmware. Reload the firmware supplied with your software version. Several software versions can coexist in separate folders. Source: openQCM support archive (11 threads) ### How do I reinstall the firmware on a Q-1 or Wi2? *Applies to: Q-1, Wi2* 1. Install the Arduino IDE and the Teensyduino add-on from PJRC. 2. Open the complete firmware folder for your instrument and board, including its libraries: Teensy 4.0 on current units, Teensy 3.6 on older Q-1, Teensy 3.2 on older Wi2. A missing "src/…" file means an incomplete folder; a missing `Adafruit_MCP9808.h` is added through the Library Manager. 3. Under *Tools* select the board and port, and for a Teensy 4.0 set CPU Speed to 150 MHz as in the mounting manuals. For a Teensy 3.2 also set USB Type to Serial. 4. Upload, pressing the button on the Teensy if prompted. Warnings such as "unused variable" are normal. If you received a compiled HEX file, flash it with the Teensy Loader instead. After a correct upload the blue LED lights and the software detects the device. Never load Teensy 4.0 firmware on a 3.2 board: the counting code differs and frequencies come out wrong. Support can guide you remotely. Source: openQCM support archive (20 threads) ### How do I check and update the firmware and software of openQCM NEXT? *Applies to: NEXT* Check the installed firmware with *Info › Firmware Info* . Keep software and firmware up to date and read the release notes: recent releases improved resonance signal processing, added selectable datalog sampling times and the Log Data View and Raw Data View windows, and fixed temperature-control alerts. Some releases need a matching firmware; a mismatch can cause serial errors, measurement loops or temperature-control problems. Firmware updates come as a HEX file with a loader tool: 1. Open the loader and load the HEX file ( *File › Open HEX File* ). 2. Press the small reset button through the hole in the main unit with a thin pin. The board enters programming mode and the firmware is written; the fan stops briefly and restarts. 3. Restart the software and check the version again. The open-source firmware can also be compiled with the Arduino IDE and Teensyduino. If a new version misbehaves, go back temporarily to the previous one in its own folder and report the problem with console screenshots. Source: openQCM support archive (9 threads) ### Under which licence is openQCM released, and can I modify it or build my own? *Applies to: all instruments* openQCM is open hardware and open source under the **Creative Commons BY-NC-SA 4.0** licence: you may study, modify and share the designs and code for non-commercial purposes, with attribution and under the same licence. Commercial or OEM use needs an agreement with openQCM. - **Software and firmware** : Python software and Arduino/C++ firmware, downloadable with earlier versions. Users have added pump control, cameras, timers and translated interfaces. - **Hardware** : schematics, CAD files of cells and modules and construction files are shared on the website or on request. Typical uses are teaching labs, custom or confinement cells built around the sensor module, and integration with LabVIEW or MATLAB through the USB serial port. Building a working Q-1 or NEXT from parts needs specific mechanical and electronic know-how: sealing, contact pressure and thermal noise are critical, and support cannot guide complete self-builds step by step. Source: openQCM support archive (15 threads) ### Can I change the software interface or its processing parameters? *Applies to: Q-1, NEXT* Yes, with the source version (the Windows executable cannot be edited). Back up the files and change one thing at a time. - **Processing parameters** are in `constants.py` (in `core`): smoothing window, sweep span and step, peak-search distances. You can also open it as text to cite the values you used. - **Smoothing and response time** (Q-1): frequency and dissipation pass through a circular averaging buffer, 50 samples by default (about 30 s), and a Savitzky–Golay filter. This is why "processing early data" appears after Start. A shorter buffer responds faster but is noisier. - **Interface** : the layout is a Qt Designer file (for example `res/mainWindow_new.ui`), which is also where labels are translated. Compile it with `pyuic`, copy the result into the `ui` folder and connect new buttons in `mainWindow.py`. Users have added timers, event markers, normalised shifts (Δf/n), mass displays and pump triggers. Check the latest release first, since many such features are added there. Firmware parameters, such as averaging or gate time, need a re-upload with the Arduino IDE. Source: openQCM support archive (15 threads) ### Why do the live plots differ from the CSV values, and how do I see small shifts? *Applies to: Q-1, NEXT* **Set Reference** works like the tare of a scale: from that moment the plots show Δf (Hz) and ΔD relative to the reference, so all overtones appear around zero. **Reset Reference** returns to absolute values. Without a reference the NEXT plots absolute frequencies, which differ by megahertz between overtones. Plots in the manuals usually show shifts. After a large step such as air to buffer (hundreds or thousands of hertz), a later binding step of a few hertz looks flat on an auto-scaled plot. Wait for a stable baseline, then press **Clear Plots** and **Set Reference** , and allow time for slow binding to develop. These controls only change the display. The CSV files keep absolute values: to reproduce the shift plots, subtract the values of your reference row from all later rows, separately for each overtone. You can then choose any baseline during analysis. Source: openQCM support archive (7 threads) ### How do I zoom the live plots, and why do I see only part of a long run? *Applies to: Q-1, NEXT* - **Zoom** : the charts use pyqtgraph. Right-click › *Mouse Mode › 1 Button* lets you draw a rectangle; the scroll wheel zooms the axes; the "A" button or *View All* autoscales. During acquisition the plots rescale themselves, so stop first to set fixed axis ranges. - **Long runs** : to stay responsive, the live chart shows a moving window of recent data (on the Q-1, the last 180 minutes). Acquisition continues and every point is written to the data file; plot the complete run from the file afterwards. - **NEXT minimum scale** : the frequency plot does not zoom below ±100 Hz, on purpose, so that normal sub-hertz fluctuations do not look alarming. Use the Log Data View add-on for full autoscaling, or ask support for a modified source file. - The time axis shows clock time; elapsed time is in the relative-time column of the file. For publication figures, plot the CSV in your own software. Source: openQCM support archive (10 threads) ### Can I run several openQCM instruments from one computer? *Applies to: all instruments* Yes. Each instrument drives one sensor, and you run one software instance per instrument: 1. Make a separate copy of the software folder for each device; each copy saves its data in its own folder. 2. Connect each instrument to its own USB port. Direct ports are preferable to hubs; with a hub, watch for ground loops. 3. Let Windows recognise each device, then start each copy and select a different COM port. Fixing the COM numbers in Device Manager helps. 4. On the Q-1 and NEXT, measure on the same COM port used for calibration. Users have run four or more devices in parallel on an ordinary laptop. Disable sleep, keep free disk space and use stable USB ports. With several Q-1 instances the logging interval can differ slightly between devices; setting the main-loop timer in `constants.py` close to the sweep time evens this out. Showing several devices in one window would need major software changes. For synchronised multichannel systems, contact openQCM about custom designs. Source: openQCM support archive (29 threads) ### Can I sample faster than once per second with the Wi2 or other oscillator boards? *Applies to: Wi2, Holder* Oscillator boards (Wi2, Teensy shield with the Holder) count the crystal's pulses over a fixed gate time, 1 s by default, so the counting resolution is about 1/gate: 1 Hz at 1 s, 10 Hz at 100 ms, about 1 kHz at 1 ms. A shorter gate updates faster but more coarsely. A moving average of ten 100 ms readings restores roughly 1 Hz smoothing while updating every 100 ms. To change the gate, edit the gate constant in the open-source firmware (for example `#define GATE 1000`, in milliseconds), scale the count to Hz if needed, and upload again with the Arduino IDE and Teensyduino. Constant names differ between firmware versions, so ask support if in doubt. Do not compute the gate in seconds with integer division: `GATE/1000` is zero for gates below 1000 ms. The serial baud rate does not set the sampling rate, and thousands of readings per second are not practical by counting at MHz frequencies. Source: openQCM support archive (6 threads) ### What is the serial output format of the Wi2 firmware, and why does the raw data contain spikes? *Applies to: Wi2, Holder* The oscillator firmware sends one line per gate period over USB serial at 115200 baud, in the form `RAWMONITOR_`, followed by a terminating byte of value 255. The frequency is the counted value in Hz; the temperature is the MCP9808 reading in °C multiplied by 10, as an integer (241 means 24.1 °C). A serial monitor shows this output, which is a quick check that the main unit works independently of the PC software. If no temperature sensor is connected, set the temperature to 0 in the firmware. Raw readings occasionally contain a spike pair: the hardware counter is read slightly late, giving one count too high followed by one too low. This is normal. The openQCM software filters it; in your own code, keep a circular buffer of at least five readings and output the median. Source: openQCM support archive (4 threads) ### Why does a 10 MHz crystal read about 6 MHz, or why do the 6 and 10 MHz settings look swapped? *Applies to: Wi2* (Legacy: first-generation openQCM, blue case with Arduino Micro and oscillator shield, now discontinued.) The Arduino Micro counts pulses with a 16 MHz clock, so it measures correctly only up to about 8 MHz. Above that, undersampling occurs: a 10 MHz crystal reads about 6 MHz, and changes appear with the opposite sign. The legacy software therefore asks you to choose 6 or 10 MHz and reconstructs the true frequency as `f = 2 × 8 MHz − fcounted`; frequency changes remain correct. If you see this on a **Wi2** , you are using the first-generation software. The Teensy-based Wi2 counts directly into the tens of MHz and needs no correction: install the current Wi2 software. The Wi2 ships with the right firmware. If you write your own code for a first-generation board, reload the firmware made for it, because the old Java software expects a different output format. Source: openQCM support archive (11 threads) ### My early Q-1 came with Java software. How do I move to the current Python software? *Applies to: Q-1* (Legacy: early Q-1 units delivered with the Java beta software and a Teensy 3.6.) In that software a SCAN was needed before each measurement to correct the gain baseline, START was enabled only after the scan, and data were saved only with SAVE FILE. Each firmware version worked only with its own Java version, so messages such as "Error during calibration, please repeat after disconnecting/reconnecting" usually meant a firmware–software mismatch. The Java software is no longer developed. To upgrade: 1. Flash the firmware for the Python software with the Arduino IDE and Teensyduino (see the firmware question). Java and Python firmware cannot coexist. 2. Install the current Q-1 Python software. 3. Calibrate each new crystal, then measure; data are saved automatically. Contact support for the files for your unit. If calibration still fails, check the crystal contact and calibrate a clean, dry crystal. Source: openQCM support archive (13 threads) ## Cleaning & maintenance ### How do I clean the microfluidic channels? *Applies to: NEXT* The inlet/outlet channels are less than 1 mm in diameter and can clog with solid or solidified residues, which during pumping may cause overpressure, fluid loss, or crystal breakage. Before each experiment, check that the channels are clear and clean if needed: 1. Use a single-wire electrical conductor segment with an outer diameter no more than 0.75 mm. 2. Insert the wire through the channel hole and gently pull it through; if it resists, try inserting from the other end. 3. Move the wire back and forth a few times, then pull it out. 4. Repeat for the other channel. **Do not** use needles or rigid wires — the PTFE core has very thin walls and can be perforated, rendering it unusable. Source: openQCM NEXT user guide, p.22 ### How do I clean and reassemble the NEXT sensor module? *Applies to: NEXT* Clean all sensor-module components periodically, since small leaks from misplacement of the sensor or improper cover mounting can deposit fluid on the temperature sensor or electrical contacts and interfere with signals and thermal control. Disassemble the module, remove the quartz sensor and the PTFE fluidic core, unscrew and set aside the two proximity-electronics screws, remove the half o-rings ( **do not unscrew the 2 grub screws near the half o-rings** ), and place components in a beaker partially filled with isopropyl alcohol. Put the beaker in an ultrasonic cleaner partially filled with pure water and clean for at least 15 minutes. Let parts dry (nitrogen gas improves drying) and ensure the inlet/outlet channels are dry before reassembly. Source: openQCM NEXT user guide, p.23-25 ### How should I handle and clean the quartz sensors? *Applies to: NEXT* To avoid damage or scratches, handle quartz sensors with dust-free lab gloves and soft-tipped tweezers, preferably Teflon, and ideally use the openQCM Teflon holder. The suggested cleaning protocols are generally not harmful to sensor coatings, but success is not guaranteed and depends on the deposited materials. For gold-electrode sensors, the manual references published regeneration/cleaning protocols, including Wasilewski et al., *Biosensors* 2022, 12, 309, and Fulgione et al., *Sci. Rep.* 8, 16137 (2018). Source: openQCM NEXT user guide, p.26 ### How do I clean the NEXT electrochemistry module components? *Applies to: NEXT* Disconnect all electrical connections and power down before cleaning, then disassemble in reverse order (steps 5 through 1). Clean the PTFE cover/fittings and the PTFE reservoir with deionized water or mild detergent (isopropyl alcohol for stubborn residues), the quartz cylinder with deionized water and mild detergent dried with lint-free tissue, and the sensor holder contacts with isopropyl alcohol on lint-free swabs; inspect O-rings and replace if degraded. Alternatively, ultrasonically clean removable parts in isopropyl alcohol at room temperature for two consecutive 5-minute cycles, rinse with deionized water, and dry (the quartz cylinder may be oven-dried at 40 °C for 30 minutes). **Never use acetone or aggressive organic solvents** , which can damage sealing surfaces. Source: openQCM_NEXT-Electrochemistry-Module, p.28-29 ### Can I use the Q-1 PMMA window cell with organic solvents? *Applies to: Q-1* No. It is strongly suggested **not** to use the PMMA (acrylic glass / Plexiglas®) window cell with organic solvents, because PMMA swells and dissolves in many organic solvents such as ethanol and has poor resistance to chemicals that hydrolyse its ester groups. The standard window cell is available in PMMA or PTFE (Teflon®); for aggressive media choose PTFE, and always be careful with aggressive chemicals. Source: openQCM_Q-1-user_manual, p.37 ### How do I clean the Q-1 EQCM module components? *Applies to: Q-1* Disassemble in reverse order of assembly and, with all connections disconnected, clean each part: - **PTFE cover/fittings and PTFE reservoir** : deionized water or mild detergent; isopropyl alcohol for stubborn residues. - **Quartz cylinder** : handle with extreme care, deionized water (mild detergent if needed), dry with lint-free tissues. - **O-rings** : inspect for wear and replace if degraded. - **Sensor holder contacts** : clean with isopropyl alcohol and lint-free swabs. Alternatively, ultrasonically clean removable parts in isopropyl alcohol (two 5-minute cycles), then rinse with deionized water. **Never use acetone or aggressive organic solvents** , and ensure parts are fully dry before reassembly. Source: openQCM_Electrochemistry-Module-User_Manual, p.28-29 ### What are the temperature, voltage and handling limits for the Wi2? *Applies to: Wi2* The device case is 3D-printed in **Nylon (PA2200)** , which is heatproof to **80 °C / 176 °F** and dishwasher safe; higher temperatures may significantly change the material's properties. The recommended working temperature range for the electronics and device is **−40 °C to 85 °C** . The device must be powered only at a continuous **5 VDC** via USB – a different power supply will damage it – and, due to its open-source construction, the user should take appropriate precautions against electrostatic discharge. Source: openQCM_Wi2-user_manual.pdf, p.13, p.14, p.15 ### What safety and handling precautions should I follow? *Applies to: SpaceBug* Observe these precautions to avoid injury and damage: - Do not use the device near flammable gases, fumes, or liquids, and do not expose it to rain, snow, or dust; keep it dry during storage and transport. - Do not use force when connecting or disconnecting connectors, and do not subject the equipment to external shocks. - Always ship the product in its original Novaetech packaging or equivalent, and follow all instructions in order — skipping steps can damage the device. Source: openQCM SpaceBug.pdf, p.9 ### How do I clean the openQCM Q-1 / Wi2 sensor module? *Applies to: Q-1, Wi2* Disassemble and clean the module in solvent as follows: 1. Remove the anti-slip bumpons and unscrew the four screws at the base. 2. Unscrew the two indicated screws (keeping the spacer rings) and remove the electronic board by pulling it vertically with two fingers; tilt it once the pogo pins are exposed to free the USB connector. 3. Place all components in a beaker partially filled with **isopropyl alcohol** . 4. Put the beaker in an **ultrasonic cleaner** partially filled with pure water. 5. Let the components dry (an optical cloth or drying with **nitrogen gas** improves efficiency), then reassemble the fluidic module. The LED pins may bend during board removal; restore them on reassembly by inserting the LED into its slot first. Source: Sensor_Module_Cleaning.pdf, p.6-7 ### How should I handle a QCM sensor to avoid damaging it? *Applies to: all instruments* To prolong sensor life, minimize direct contact with the coated surfaces. Where possible use a Teflon sensor holder rather than handling the sensor directly. When using tweezers, **grip the sensor only on the edge** to avoid scratching the surface. When rinsing, direct the flow *towards* the tweezers, which reduces the risk of transferring contaminants from the tweezers onto the sensor. Source: cleaning_and_immobilization_protocols.pdf, p.2 ### How do I clean a QCM sensor with UV/ozone treatment? *Applies to: all instruments* UV/ozone treatment removes low-molecular-weight hydrocarbons through oxidation and is applicable to all sensor surfaces unless oxidation is undesired (it is **not used for silver, QSX 322** ). It does not remove thick organic films. 1. Place the sensor surfaces in a UV/ozone chamber, approximately **5 mm from the lamp** . 2. Turn on the UV lamp for **5–10 minutes** ; a minimum of 12 mW/cm^2 at 1 inch from a 185/254 nm lamp is recommended. Source: cleaning_and_immobilization_protocols.pdf, p.3 ### How do I clean the instrument flow path on a daily basis? *Applies to: all instruments* Contamination of the flow system is a common cause of drifting measurements, so clean it after each measurement and finish with a pure-water rinse. 1. Mount a sensor surface into the chamber/flow module. 2. Pump approximately **20 ml of 2% Hellmanex II** through the system (heating to 30°C can improve cleaning). 3. Pump **100 ml of milliQ water** through the system. 4. Empty the chamber/flow module and dry the visible parts with nitrogen gas. Source: cleaning_and_immobilization_protocols.pdf, p.9 ### How do I perform a thorough cleaning of the flow module? *Applies to: all instruments* For a deep clean of the flow module: 1. Open the module and unscrew the 6 screws holding the flow part together (PH-1 screwdriver). 2. Pry or twist the two metal pieces apart and remove the sealing gasket and o-ring. 3. Immerse all flow parts in **2% SDS in milliQ water** . **Important:** the contact block with the two electrode pins must never be immersed in any cleaning solution. 4. Sonicate while heating to **40°C** . 5. Rinse with milliQ water and dry with nitrogen gas. 6. Optionally replace the gasket and o-ring, then reassemble — take care not to overtighten the 6 M2 screws. Source: cleaning_and_immobilization_protocols.pdf, p.10 ### How should lipid vesicle solutions be stored before functionalizing a sensor? *Applies to: all instruments* After preparation and sonication, lipid vesicle solutions (for example POPC-based vesicles used to form supported bilayers) should be stored at **4°C under nitrogen or argon, in darkness** . When applying bilayers, de-gas the buffer (e.g. by sonication) before flowing it through the QCM-D chamber to avoid air-bubble formation. Source: cleaning_and_immobilization_protocols.pdf, p.12-13 and p.16-17 ### Can openQCM gold sensors be cleaned and reused, and which regeneration method is least damaging? *Applies to: all instruments* Yes. A study using openQCM (Novaetech) AT-cut 10 MHz gold sensors compared three regeneration methods for peptide-coated electrodes: **Piranha solution** , **oxygen plasma** and **electrochemical (cyclic voltammetry) cleaning** . All three removed the peptide layer, but they differ in how much they erode the gold. After three regeneration cycles the loss of sensor performance was about **25% for Piranha, 16% for oxygen plasma, and only 7% for the electrochemical method** . Electrochemical cleaning was the least invasive and most reproducible, best preserving the gold surface and extending sensor lifetime. Source: CLEANING-biosensors-12-00309-v2.pdf, p.1, p.10-12 ### How is oxygen plasma cleaning applied to QCM sensors, and what are its effects? *Applies to: all instruments* Oxygen plasma rapidly removes organic contaminants and sulphur from the gold surface and does not react with silicon dioxide, so the quartz properties are unchanged. In the reported work, cleaning was done in a plasma generator for **85 s at 0.5 mBar and 22 W** , after which the sensor was placed in deionized water for 3 min, transferred to methanol, and dried in a desiccator (12 h). The treatment causes slight surface oxidation, forming a protective gold-oxide (Au_2O_3) layer; this oxidation can later make covalent re-attachment of peptides more difficult. Plasma is less invasive than Piranha but still slightly reduces sensitivity over repeated cycles. Source: CLEANING-biosensors-12-00309-v2.pdf, p.4-5 and p.11-12 ### After a QCM-D binding experiment, how do I clean the system to avoid contamination? *Applies to: all instruments* Once a measurement script is finished, run a washing routine using a **sodium dodecyl sulphate (SDS) surfactant solution** over the sensors, syringes and tubing, then finally rinse with MilliQ water and leave to dry overnight. This leaves the system clean and dry for the next experiment. In a customized openQCM (C-QCM) flow setup, the ports, tubing and sensor holders are likewise cleaned with maintenance chips before each session, with the system held at room temperature (25°C). Source: se0c01641_si_001.pdf, p.4 ### How should I store new crystals, and do they need cleaning before first use? *Applies to: all instruments* Crystals are supplied in boxes of 10, in a vacuum-sealed bag. Once the bag is open, store them dust-free in **dry air or nitrogen at room temperature** . Yes, clean new crystals too: gold readily picks up contaminants during transport and storage. A gentle start is a rinse with deionised water and methanol or ethanol, then drying with nitrogen or in a desiccator. Handle crystals by the edge with dust-free gloves and soft-tipped tweezers, preferably PTFE. Avoid touching the electrodes, which would leave residues that shift the baseline. Source: AT5-14-12-AU-WRAP datasheet, p.5; AT10-14-12-AU-WRAP datasheet, p.6; Wasilewski et al., Biosensors 2022, 12, 309, p.2-3; openQCM NEXT user guide, p.26 ### How many times can I reuse a crystal, and when should I replace it? *Applies to: all instruments* Treat crystals as consumables: a fresh crystal for each experiment gives the most reproducible results. In practice crystals can often be cleaned and reused, many times with mild samples and gentle cleaning, but only a few times (or once) when the layer binds chemically or aggressive cleaning such as piranha is needed. Each cleaning removes a little electrode material, so sensitivity can fall slowly. Heavily modified surfaces (cross-linked polymers, cured films) may never come fully clean. Check the crystal after each cleaning and replace it when: - its frequency or resonance amplitude in air no longer returns close to the bare-crystal values; - the baseline is noisier or drifts more than usual, or calibration finds weak or missing peaks; - the electrode is scratched, chipped or cracked, or results stop being reproducible. For gold electrodes, the peak separation in a cyclic voltammogram of ferri/ferrocyanide is a further cleanliness check. Simply rinsing a water-soluble film off with water does not harm the crystal. Source: openQCM support archive (25 threads) ### How should I store SiO₂-coated sensors, and why does my coating look patchy? *Applies to: all instruments* Once the vacuum bag is open, store all crystals dust-free and dry (dry air, nitrogen or a desiccator) at room temperature. This matters most for oxide and silicon-based coatings: they absorb moisture and can become unusable if kept in a humid lab for long periods. A cloudy or stained coating on a crystal that has never been used points to moisture uptake. SiO₂ is more delicate than gold. A patchy or scratched look on arrival or after use is usually delamination, because SiO₂ adheres poorly to gold. Current SiO₂ sensors include an extra titanium adhesion layer to prevent this; report affected sensors to support. Clean SiO₂ surfaces with UV/ozone, oxygen plasma or the SDS protocol, and avoid aggressive etching that thins the layer. Full restoration is not always possible, so treat coated sensors as single-use for critical work. The coating is applied to the sensing face only. Source: openQCM support archive (4 threads) ### How do I replace the window of the Q-1/Wi2 fluidic cover, or reset its height? *Applies to: Q-1, Wi2* 1. Remove the old window by loosening the three set screws with the 1.3 mm micro hex key. 2. Fit the new window, with its O-ring lightly greased in the groove, and turn the screws only slightly, so the window can still move up and down. 3. Remove the crystal from the sensor module and place the cover on the module. 4. Set the lever halfway between min and MAX. 5. Press the window gently until its O-ring touches the O-ring of the module, then tighten the three screws to fix the height. Do not overtighten: PMMA can crack. 6. Remove the cover, insert the crystal, refit the cover and move the lever gently toward MAX. 7. Run the syringe leak test. If the level in the tube drops, move the lever slightly further toward MAX; if it still drops, repeat from step 3. Occasional readjustment of the window height is normal over the life of the cover. Source: openQCM support archive (2 threads) ### How do I clean the PMMA window of the Q-1/Wi2 cover, and can scratches be removed? *Applies to: Q-1, Wi2* Usually only the transparent PMMA (acrylic) window needs cleaning. Wipe it with a lens cloth moistened with isopropyl alcohol; this should not damage the plastic, though it can slowly discolour it. If the window is very dirty, unscrew it from the cover, remove the O-ring and clean the window in an ultrasonic bath with **pure water** first. Use isopropyl alcohol only if needed, because there is some risk of damaging PMMA, and never use other organic solvents. Dry it fully before reassembly and tighten the set screws gently. Scratches can be removed, for example for microscope observation, by polishing progressively from coarser to finer grits and finishing with a plastic polish. A scratched window can also stop the liquid from wetting the crystal completely, so polish or replace it. For solvent work use the PTFE-window cover instead. Source: openQCM support archive (2 threads) ### How tight should the screws of covers and modules be? *Applies to: all instruments* Gently. Several parts thread into **PTFE or nylon** , and these threads strip easily. Tighten by hand with a small screwdriver and **stop as soon as you feel resistance** . Overtightening also deforms PTFE parts, which can break the seal and cause leaks, and it stresses the crystal, which shows as drift or cracking. - Use only screws of the original length. Longer screws can press on PTFE parts or stop a cover from seating. - On stacked parts, such as the quartz holder, tighten evenly in a diagonal sequence. - The NEXT fluidic cover is held by small stainless-steel set screws and slotted round nuts. Tighten them evenly and only enough to close the cell. Spare screws and O-rings come with the instruments. The screws are standard small metric parts, so replacements are also available from fastener suppliers. Source: openQCM support archive (4 threads) ### Which O-rings does the sensor module use, and can I fit a more solvent-resistant material? *Applies to: Q-1, Wi2, NEXT* The crystal seal uses standard FKM (Viton®) O-rings of about 11 mm inner diameter. On the Q-1 and Wi2 one ring is cut into two halves to support the crystal, and the module also has a larger ring for the 1-inch seat. Sizes quoted in different documents vary slightly, so use the replacement O-rings supplied by openQCM, or match the original ring exactly. For solvents that swell FKM (for example some polar aprotic solvents such as DMF), fit a perfluoroelastomer (FFKM, Kalrez-type) or other resistant ring of the **same size** . Keep the hardness similar or softer: a harder ring needs more pressure to seal and stresses the crystal, which shows as drift. Do not use a ring with a larger inner diameter (for example 12 mm), which may not seal. Inspect the O-rings at every crystal change and replace any that are deformed, swollen or cracked. Spare O-rings come with the instruments and are also available separately. Source: openQCM support archive (11 threads) ### How do I adjust or repair the pogo-pin contacts in the Q-1/Wi2 sensor module? *Applies to: Q-1, Wi2* The pins should stand just above the support O-ring, so they touch the crystal pads without lifting it. Too low gives a weak or missing signal; too high tilts or stresses the crystal, causing drift, noise, or a crack when the cover closes. - **Height** : with the crystal removed, insert the 1.3 mm hex key through the small hole under the module (it reaches the pin-height set screw) and turn in small steps. Check with a crystal and the cover closed; you can also watch the live signal until a clean resonance curve replaces the noise. - **Levelling** : if one pin is higher, remove the base cover and turn the two board screws slightly until the pins are even. Do not force them. - **Cleanliness** : deposits or corrosion on pins or pads add resistance. Clean with isopropyl alcohol on a lint-free swab. - **Unsoldered pin** : a spring pin that has come off its pad can be resoldered with ordinary soldering. Readjust only when you see contact problems, tilt or drift. If unsure, send photos of the pins and board to support. Source: openQCM support archive (13 threads) ### Can I replace the proximity board of the sensor module myself? *Applies to: Q-1, Wi2* Yes. The proximity board, the small board under the crystal that carries the pogo pins, the temperature sensor and the status LED, is a user-replaceable spare part. Spare boards and complete sensor modules fit existing main units. 1. Disconnect the device and remove the crystal, the bumpons and the base cover. 2. Undo the two board screws (keep any spacers) and lift the board out, taking care with the LED and the pins. 3. Fit the new board and reassemble. 4. Set the pin height with the 1.3 mm hex key so the pins just protrude above the O-ring. 5. Check that the LED lights and the temperature reads sensibly, then calibrate with a crystal as usual. No other calibration is needed. A spare kit may contain a small two-terminal component: the status LED. Solder its longer lead (anode) to the "+" pad and the shorter lead to "D1". It is not needed for measurements. Source: openQCM support archive (9 threads) ### My instrument seems faulty. How do support and repairs work? *Applies to: all instruments* 1. Write to openQCM support with the instrument model and serial number, the software and firmware versions, the crystal type and what happened. 2. Attach screenshots of the calibration and amplitude/phase curves and of the real-time plots, your data files, and photos of the mounted crystal, contacts and boards. 3. Many problems (contacts, leaks, firmware, software settings, COM ports) are solved remotely, by e-mail or in a remote-desktop session. 4. If a part is faulty, support can send a replacement, such as a proximity board or sensor module, which you can usually fit yourself. 5. If the instrument must come back, support explains the shipping procedure. Decontaminate any part exposed to hazardous or biological samples, include all modules so they can be tested together, and use the original or equivalent packaging. Returned instruments are inspected, repaired and tested again before they are shipped back. Avoid hardware modifications that the manuals do not describe. Source: openQCM support archive (52 threads) ### Which spare parts can I get? *Applies to: all instruments* Spare O-rings and screws come with the instruments. Other parts are in the online store or can be ordered on request: - proximity boards (contacts and temperature sensor) and complete sensor modules, which fit existing main units; - top fluidic covers with PMMA or PTFE windows (also without inlet and outlet holes), open and pipetting covers, levers; - NEXT fluidic, pipetting and optical modules, or their covers alone; - electrochemistry cell parts and quartz holders; - O-rings, contact pins, screws, tubing and the micro hex key; - microcontroller boards and cases; - crystals: 5 MHz, 10 MHz and SiO₂-coated. When you ask, give the model and serial number so support can identify your hardware revision; for example, older top covers held only by magnets differ from the current lever design. Standard parts such as O-rings, screws and connectors can also be bought from distributors, and schematics and pinouts are available on request. Source: openQCM support archive (20 threads) ### The quartz cylinder of my electrochemistry cell broke. Can it be replaced? *Applies to: Q-1, NEXT* Yes. Contact support for a spare cylinder. Glass and quartz parts have loose tolerances, so replacements are selected to fit the PTFE reservoir of the cell. A machined PTFE cup is a possible alternative, and support can provide the CAD files of the chamber for it. To avoid breaking the new one: - handle it with gloves and safety glasses; - lower it vertically onto its seal without twisting or forcing it; - turn the fixing ring only until you feel moderate resistance. Full tightening is neither needed nor recommended. Clean the cylinder with deionised water or a mild detergent and a lint-free tissue, never with abrasives, acetone or aggressive organic solvents. Source: openQCM support archive (1 thread) ## Troubleshooting ### My Q-1 frequency keeps drifting after mounting the sensor — what should I do? *Applies to: Q-1* Frequency drift can occur when the fluidic cover presses too hard on the quartz surface. You can solve this by finely tuning the lever *clockwise* toward the minimum direction to reduce the pressure. **Be careful** : turning the lever clockwise too far may cause the cell to lose its seal and flood, so adjust gradually and re-check the seal. Source: openQCM_Q-1-user_manual, p.11 ### I'm seeing frequency drifts after sealing the cell — how do I fix it? *Applies to: Wi2* Frequency drifts can occur when the cover presses too hard on the quartz surface. To solve this, finely tune the lever **clockwise** toward the minimum direction to relieve the pressure. **Be careful** : turning the lever clockwise too far may cause the cell to lose its seal and flood, so adjust gradually. Source: openQCM_Wi2-user_manual.pdf, p.9 ### What safety precautions and handling rules should I follow with the openQCM TWIN? *Applies to: TWIN* Follow these precautions to avoid injury and damage: - Do not use the device near flammable gases, fumes, or liquids; it is for indoor use only and must not be exposed to rain, snow, or dust. - Avoid temperatures below 0°C and above 50°C during storage and transport. - Do not use force on connectors and do not subject the board to shocks. - If liquid is spilled on the instrument, disconnect power and have it checked; do not perform unauthorized modifications. Source: openQCM_TWIN_User_Manual.pdf, p.7 ### What does it mean when the onboard LED blinks, and how do I handle SD card failures? *Applies to: SpaceBug* The firmware uses the built-in LED for status feedback: if SD card initialization fails, an error message is printed to the serial monitor and the `led_Blink()` function blinks the LED **three times** . To make SD operation more robust, the manual suggests adding a retry mechanism that attempts `SD.begin()` several times (e.g. up to `MAX_INIT_ATTEMPTS = 3`) before giving up, which improves the chance of success after temporary issues. Also double-check wiring and confirm the chip-select pin definition matches your hardware. Source: openQCM SpaceBug.pdf, p.24, 27, 29 ### Can I plug the openQCM Holder into a standard USB port on my computer? *Applies to: Holder* **No.** The openQCM Holder fitted with the USB connector is **not compatible with standard USB ports** because its pinout allocation is different. Connecting it to a standard USB port could damage the device. The USB connector is intended for use with your own custom acquisition electronics wired to the documented pinout (e.g. pin 2 QCM OUT, pin 3 QCM IN, pins 1/9 the I2C temperature sensor SDA/SCL, pin 6/8 GND, pin 7 V+). Source: openQCM Holder.pdf, p.8 and p.10 ### My crystal looks clean but shows no resonance at all. Could the electrode connection be broken? *Applies to: all instruments* Possibly. openQCM crystals use wrapped electrodes: the large top (sensing) electrode continues around the edge of the quartz disc to a pad on the back, so both contacts are made from below. If the thin gold strip along the edge wears away, through repeated or aggressive cleaning, abrasive handling or long oxidising treatments, the top electrode is disconnected. The crystal can no longer be driven and calibration finds no peak, even though both faces look fine. Inspect the edge under a magnifier before reusing a crystal, and use the mildest cleaning that works. The same happens with a home-made sensor: a conductive film deposited on a bare quartz blank without a wrap-around tab is electrically floating. It can be rescued by bridging the top film to the back pad around the edge with a silver-filled conductive epoxy (low-outgassing grades exist for vacuum work); the edge region is not very mass-sensitive. For new work it is simpler to start from wrapped-electrode sensors and deposit your material on top. Source: openQCM support archive (4 threads) ### The cell still leaks after I close it. How do I find the cause? *Applies to: Q-1, Wi2, NEXT* First run the usual aspiration test: inlet tube in a water reservoir, syringe on the outlet, stop before the liquid reaches the chamber. To **locate** a leak, pull harder on the syringe and watch where air bubbles enter. Common causes: - an O-ring that is worn, swollen, of the wrong size or badly seated; - a crystal that is not centred or not flat, leaving a gap under the O-ring; - too little closing force: on the Q-1/Wi2 move the lever a little further toward MAX; on the NEXT tighten the nuts evenly; - missing window set screws, overlong screws, or overtightened PTFE parts that deform the seal; - broken tube connectors, or overpressure from pushing liquid in. Use the lowest closing force that passes the test: excess pressure stresses the crystal and causes drift. Colloids and low-surface-tension liquids may need a little more. If a Q-1/Wi2 cover still leaks, reset the window height. Repeat the test at every crystal change, because crystals from different batches can differ slightly at the edge. A brief movement of the liquid that then stops is normal. Source: openQCM support archive (29 threads) ### The software warns 'unable to apply half-power bandwidth method' or 'right/left value not found'. Are my data still valid? *Applies to: Q-1, NEXT* The frequency is taken at the peak of the swept resonance curve, and the dissipation from the curve width where it crosses a calibrated level on each side. The warning means one crossing was not found inside the sweep window: the peak has moved or broadened beyond it (heavy or viscous loading gives "left", a frequency increase gives "right"), or it has become too weak (poor contact, leak, bubbles, strong damping). - **Validity** : frequency usually stays valid while the peak is inside the window; dissipation does not. A single warning in a long run is at most one outlier point; frequent warnings mean the dissipation is unreliable. - **Fixes** : calibrate the clean crystal in air before adding liquid, recalibrate after a large mass change, update the software (recent versions sweep a wider window and can calibrate in liquid), and check contacts, leaks and pump speed. - **Wider window** : on the Q-1 it is set in `constants.py` of the Python source, not in the executable. Each sweep has a fixed number of points, so a wider window means a coarser step and noisier values. Widen only as needed. Source: openQCM support archive (77 threads) ### The software stops acquiring, freezes or crashes during a long run. What can I check? *Applies to: Q-1, NEXT, Wi2* The software has no time limit, so a run that stops by itself has a technical cause. - **PC power settings** , the most common cause: disable sleep, hibernation, disk sleep and USB selective suspend, and avoid automatic restarts for updates. Screen standby alone is harmless. - **The live data file** : never open or copy it during acquisition. Exclude the data folder from cloud synchronisation (OneDrive or similar) and from real-time antivirus scanning; a "PermissionError" after hours usually means something touched the file. - **Installation** : extract the archive completely into a short path where you have write permission. Problems after one or two uses suggest antivirus quarantine; re-extract a fresh copy. If "Run as administrator" fails, start `app.exe` from an administrator command prompt in its folder. - **Hardware** : use a reliable USB cable and port, stop the measurement before removing the crystal, and check seating and leaks, since losing the resonance can stall tracking. - Enough memory and disk space, and the latest software with matching firmware. If it repeats, send support the console output, the data file and the time of the stop. Source: openQCM support archive (14 threads) ### The liquid does not fill the chamber completely, or leaves dry spots on the crystal. What can I do? *Applies to: Q-1, Wi2, NEXT* - **Fill fast, then slow down.** Low flow rates often fail to wet the whole chamber. Draw the liquid in quickly with a hand syringe on the outlet until the chamber is full, then continue at your working rate. - **Fill by aspiration** , with the inlet in a reservoir, so the chamber fills evenly without overpressure. - **Clean the surfaces.** Contaminants on the window or crystal change the surface energy and make the liquid pin. Clean the window and use a clean crystal. - **Pre-wet** with a low-surface-tension liquid such as isopropyl alcohol, then replace it with your buffer. Avoid this with PMMA windows and sensitive biological samples. - **Clear the channels** , which are under 1 mm wide, with a thin, soft single-core wire (no more than 0.75 mm on the NEXT). Avoid rigid needles, which can perforate PTFE. An O-ring sticking to the window after the cell has stayed assembled for a long time is normal and does not affect sealing. Source: openQCM support archive (3 threads) ### How do I avoid air bubbles in the measurement chamber? *Applies to: all instruments* Bubbles add noise and steps, and as they grow they remove wetted area: frequency rises and dissipation falls, often right after the flow starts. Besides air in the tubing, they come from degassing: a liquid that warms up in the cell releases micro-bubbles. - Degas liquids (for example under mild vacuum or with sonication) and bring them close to the cell temperature. Change temperature gradually. - Use clean, hydrophilic crystals; residues act as nucleation sites. - Fill slowly and draw the liquid through the cell (pump-out). Do not let air in when switching reservoirs. - Check that tubes are fully inserted and the cover O-ring seals: small leaks draw in air. - If a bubble appears, a short, firm pull on the outlet often removes it. Do not open or loosen the cell, and do not press on the cover: this can flood the cell or break the crystal. - Look near the O-ring and the window edge. Optical and open pipetting covers trap bubbles more easily; inspect them before measuring. Source: openQCM support archive (25 threads) ### The frequency jumped up during my measurement. What should I check? *Applies to: all instruments* A QCM responds to what happens at its surface, so a rise in frequency normally means mass is leaving the surface, or the liquid coupled to it has become lighter or less viscous. Typical causes: - desorption, dissolution or evaporation, including traces of solvent leaving a "dry" sample; - air micro-bubbles on the sensor, which lower the average density in the chamber; - contamination or cleaning residues being removed; - a transient thermal or mechanical disturbance, for example breathing on the sensor, before the real signal; - on the Q-1 and NEXT, a resonance curve that is no longer fully inside the sweep window: the reported values are then not valid. Look at the real-time resonance curve first, then repeat with a fresh, clean sensor and degassed liquids. Source: openQCM support archive (5 threads) ### Liquid leaked into the sensor module. How do I recover it and stop it happening again? *Applies to: Q-1, Wi2, NEXT* Typical symptoms: temperature stuck at zero or an impossible value, frequency dropping to zero, intermittent loss of the resonance, or failed calibration. Saline buffers such as PBS are the most harmful, because their residues corrode contacts and tracks. The crystal signal path in the module has no active components, so it is usually recoverable. 1. Stop, disconnect and remove the crystal. 2. Dry everything. Liquid soaked into the module body can keep evaporating onto the back of the crystal and cause drift, so allow several days with the base cover removed if needed. 3. If symptoms persist, rinse salts off the proximity board, clean it in an ultrasonic bath of isopropyl alcohol for 15–30 min (no acetone), dry it completely, reassemble and check the pin height. 4. Mount a fresh crystal in air and calibrate again. If it does not recover, the proximity board is a user-replaceable spare part; the main unit usually survives. Corroded NEXT module contacts need service. Before measuring again, find the cause: leak test, cracked window (solvents attack PMMA), worn O-rings. Pull liquid through the cell rather than pushing it. Source: openQCM support archive (35 threads) ### The temperature reading is stuck, negative or missing. How do I find the cause? *Applies to: Q-1, Wi2, NEXT* On the Q-1 and Wi2 an MCP9808 sensor sits on the proximity board just under the crystal; on the NEXT a 10 kΩ thermistor sits below the crystal. Check in this order: 1. **Leak residues** on the sensor or its contacts, the most common cause. Clean and dry the proximity board as described for leaks. 2. **Extension cable** (Q-1/Wi2): the link between module and main unit uses USB 3 connectors that carry the crystal signals and the I²C lines of the temperature sensor. A USB 2 extension lacks those conductors: frequency still works but temperature reads zero. Use a full USB 3.0 cable, or none. 3. **NEXT** : both the USB data cable and the 5 V TEC power cable must be connected; then press *TEC Controller Reset* . 4. **Swap test** : with two units, swap the sensor modules. If the fault follows the module, its board is affected; if it stays with the main unit, suspect the connector or the internal flat cable. Damaged boards can be replaced through support. Never plug a sensor module directly into a computer. Source: openQCM support archive (19 threads) ### Is my NEXT temperature control working? The reading barely changes, or it oscillates. *Applies to: NEXT* A reading that holds the set point and barely moves usually means the controller is regulating well, not that the sensor is stuck. The 10 kΩ thermistor sits just below the crystal, so it reads the temperature inside the fluidic module. To test it, change the set point within the 25–45 °C range, for example from 40 °C to 30 °C and back: the reading should move to each new value and settle. - **Oscillation** around the set point, sometimes visible as a periodic ripple in frequency, usually comes from unsuitable PID values. Select the default PID set and change P, I and D only if needed; the user guide lists the defaults. - **After Stop** : depending on the software version, stopping a measurement can return the controller to its default state or switch it off. Switch temperature control back on if the cell should stay at temperature, otherwise it has to equilibrate again. Be suspicious only if the value never changes after a set-point change, sticks at 0, NaN or another implausible number, or a TEC error appears. Source: openQCM support archive (6 threads) ### The NEXT shows a TEC error or 'Thermal Latch-up', or stops controlling the temperature. What should I do? *Applies to: NEXT* The Peltier controller has a safety cut-out. If the heat sink overheats (long runs near the low end of the range, fast ramps down, a warm room, blocked ventilation), it switches off active control: the cell drifts toward the heat-sink temperature and new set points are ignored. - **Thermal Latch-up** : the set point cannot be reached. Let the heat sink cool, press *TEC Controller Reset* , enter the set point again and ramp gradually. - **No Sensor detected** : the thermistor is not read; the module is not fully seated, its contacts are worn or dirty, or liquid has reached them. - **No TEC detected** : the Peltier is not reached, usually a poor contact between head and main body, sometimes only when the head is tilted. Also check that the TEC power cable and adapter are connected, the fan and vents are free, and the module sits flat on the Peltier, with no grease. For long runs near 25 °C in a warm lab, add external airflow to the heat sink. If an error keeps returning, depends on the head position or follows a leak, contact support: the flat cable, thermistor or Peltier may be damaged. Source: openQCM support archive (19 threads) ### The NEXT temperature reads 0 °C, or temperature control does nothing. What should I check first? *Applies to: NEXT* The power cable. The NEXT needs two connections: the USB data cable to the computer, which powers the measurement electronics, and the USB TEC power cable from the supplied 5 V adapter (plugged into the mains) to the socket marked *5VDC* . The Peltier and the thermal control are not powered over the data cable, so without the adapter there is no control and the temperature can stay at zero. This is a common oversight at setup. Use only the supplied adapter, with a plug adapter for your country if needed. If both cables are connected: - check that the fluidic module is fully inserted (on recent units it clicks), because the thermistor contacts pass through its pogo pins; - look for liquid residue under the sensor holder; - after an error press *TEC Controller Reset* and use the default PID set. If the problem persists, send support photos of the pogo pins and of the underside of the module. Source: openQCM support archive (7 threads) ### NEXT: calibration shows no clear peaks, or the signal comes and goes. Could it be the module contacts? *Applies to: NEXT* Often yes. The fluidic module connects to the main unit through gold pads and pogo pins in its PTFE slot. - **Seating** : push the module up until it clicks (modules from 2023 onward). To remove it, press the metal clip with the supplied tool and slide it down; never lever it out, which can break the PTFE hooks. - **Quick test** : run a calibration while gently pressing the module against the heat sink. If the peaks appear only while you press, the contact is the problem. - **Condition** : pads and pins must be clean, dry and free of corrosion; saline spills such as PBS corrode them quickly. Do not apply grease or conductive paste, whose vapours can contaminate the back of the crystal. - If the same fault appears with several modules, the problem is on the main-unit side. Do not bend the slot contacts yourself. Send support photos of the module underside and of the connector on the head. Damaged connectors are repaired at the openQCM lab. Source: openQCM support archive (7 threads) ### On the NEXT I see steps or extra noise only in conductive buffers such as PBS. What can I do? *Applies to: NEXT* Conductive liquids can couple electrical interference into the crystal signal through any metal part of the cell. Current NEXT fluidic modules have a PTFE core inside a metal shell, so the liquid touches only PTFE, the O-ring and the crystal, which greatly reduces the effect. If you still see noise in liquid but not in air: - make sure the fluidic module and the heat sink share a good ground; if needed, connect them with conductive tape, a wire or a small magnet; - keep the instrument away from sources of interference; - check that no liquid has reached the contacts or electronics. On some early NEXT units with a metal top cover, insulating the cover's contact pad with tape removed step-like artefacts in PBS. Upgraded PTFE-core covers replaced those covers. Source: openQCM support archive (4 threads) ### My signal shows spikes, jumps or bursts of noise. How do I recognise electromagnetic interference? *Applies to: all instruments* The instruments are shielded but work at MHz frequencies, so nearby equipment can disturb them: mobile phones, monitors and laptops, motors, pumps, compressors, incubators, air conditioning and power supplies. Interference shows as regular spikes, jumps that recover quickly, or a noisy or distorted resonance curve, often only while the source is on. Noise that appears when someone walks in with a phone is a classic sign. It shows first on the higher overtones and in liquid, where peaks are weaker. - Move the source away or rotate the instrument; interference is often directional. - Test in a metal box connected to the ground of the USB cable. - Use short, shielded cables, no USB extensions or adapters, and with several instruments watch for ground loops through a shared hub. - Disable USB power management on the PC. Gradual drift is more often thermal or mechanical, and periodic ripple often comes from the pump. Measure a clean bare crystal in air and in static water: if its noise is normal, the cause lies in the sample or setup. Screenshots of the resonance curve in quiet and disturbed periods speed up diagnosis. Source: openQCM support archive (33 threads) ### My baseline shows a periodic ripple or slow regular oscillations. Where do they come from? *Applies to: all instruments* - **The pump** : peristaltic rollers, and diaphragm pumps, produce a regular sinusoidal ripple on frequency and dissipation. This is normal; performance figures are measured in static liquid. Use a low speed, small-bore tubing, pump-out mode downstream of the cell and a correctly closed cover. A syringe pump flows more smoothly. For the most accurate readings, exchange the liquid under flow, then stop the pump and measure static. A periodic ripple can also be filtered out in post-processing. - **Room cycles** : slow oscillations, for example every 10 minutes, whose amplitude grows with overtone number usually come from air-conditioning or thermostat cycles, cyclic equipment (vacuum pumps, compressors, shakers) or timed switching of other devices. To find the source, record a baseline in another place or at another time of day. Keep the instrument out of drafts and sunlight, on a stable bench, or in a shielded, insulated enclosure. Bring liquids to the cell temperature before they enter, and avoid emptying the cell between solutions. Source: openQCM support archive (7 threads) ### Why is the highest overtone noisier than the others? *Applies to: NEXT, Q-1* Some extra noise at higher overtones is normal: their peaks are lower, so the signal-to-noise ratio is worse, especially in liquid. For 10 MHz crystals the 5th overtone lies near 50 MHz, the top of the instrument range, where it is also more exposed to interference. Each crystal is slightly different, so some sensors show this and others do not. - Rely on the lower overtones for quantitative work when noise matters. - If you need many overtones, 5 MHz crystals reach the 9th overtone at 45 MHz, within the range. - If the noise appears only with certain crystals, try another sensor. - If the highest overtone is weak or missing on every crystal, suspect a weak contact on one pogo pin, and look for interference sources nearby. Source: openQCM support archive (9 threads) ### How can I tell whether the resonance signal is healthy, and what do weak peaks mean? *Applies to: NEXT, Q-1* Look at the amplitude curve in calibration or in the raw-data view. With a clean crystal correctly mounted, each peak stands well above the noise floor; in support experience a 5 MHz fundamental typically reaches about 10 dB or more, also in water. - **Peaks only a few hundred mdB high** : the resonance is effectively lost, through poor contact, a misoriented or cracked crystal, or leak damage. - **Peaks clearly lower than usual** : frequency and dissipation noise rise sharply. Suspect worn, recessed or oxidised pogo pins, or a heavy, thick or viscous load. - **Amplitude that comes and goes** , or depends on tilting the head: intermittent contact, or a damaged internal flat cable or connector. - **Spikes or a distorted curve** : electromagnetic interference. Test with a new bare crystal in air; with two modules or instruments, swap them to find the faulty part. Worn contact boards can be replaced; cable damage needs a repair in the lab. Send support screenshots of the amplitude/phase curves. Source: openQCM support archive (10 threads) ### Calibration shows a flat curve with no peaks, only noise. What should I check? *Applies to: Q-1, NEXT* A flat spectrum means the crystal is not vibrating or not electrically connected. Check in this order: 1. A **new, clean crystal in air** : 14 mm, wrapped electrodes, contact side down on the pins, flat and centred. If it works, the old crystal is cracked, overloaded or its edge wrap is worn. 2. The **right software** for your instrument (the Q-1 and NEXT programs are not interchangeable) and, on the Q-1, the blue LED on. 3. The **cover** : closed firmly but not pressing too hard, with no overlong or loose screws; on the Q-1, try the standard cover. 4. On the NEXT, the module **fully seated** until it clicks. 5. The **pogo pins** : not sunk, worn, dirty or unsoldered. After a leak, clean the proximity board. 6. The connectors between module and main unit. A flat spectrum while the temperature reads normally, especially if it started suddenly, points to an interrupted signal path such as the internal flat cable. Inverted peaks in a custom cell usually mean swapped input and output lines. Send support the calibration screenshot and photos of the contacts. Source: openQCM support archive (52 threads) ### Calibration reports 'incompatible peaks number or frequencies', or finds only the fundamental. Why? *Applies to: Q-1, NEXT* The calibration did not find the expected set of peaks. - **Wrong preset** : the 5 or 10 MHz option must match the crystal; a mismatch gives this error. - **Damped overtones** : a film or liquid lowers the overtones more than the fundamental. Calibrate the clean crystal in air, then coat it or add liquid. Current software accepts a calibration if at least the fundamental is found. - **Overloaded crystal** : very thick, viscous, patterned or metal-oxide coatings broaden the peaks until they sink into the noise. Use less material and keep it off the contact side and the edge wrap. A conductive coating must not short the two electrodes; check with a multimeter. - **Contacts** : loose cover screws or NEXT nuts, a module not fully seated, or discoloured or uneven pins often lose the highest overtone first. On the NEXT, check that the sensor holder is not inserted the wrong way round. - **Custom holders** : keep wires short and shielded. If a new clean crystal calibrates correctly, the instrument works and the problem lies with the coated crystal. Source: openQCM support archive (25 threads) ### The software does not find the instrument or its COM port. What should I check? *Applies to: all instruments* 1. **Cable** : connect the main unit, never the sensor module, to the PC with a USB data cable. Many cables are charge-only; try another cable and port, directly on the PC. 2. **Device Manager › Ports (COM & LPT)** : the Teensy appears as "USB Serial Device (COMxx)". Unplug the device to see which port disappears; COM1 is almost never the instrument. 3. **Driver** : Windows 10/11, macOS and Linux need none. Older Windows versions, or Teensy 3.x units, may need the PJRC serial driver, which the Arduino IDE with Teensyduino also installs. Offline PCs cannot download it automatically. 4. **Port busy** : "permission" or "cannot configure port" errors mean another program, such as a serial monitor, holds the port. Close it, replug the device and restart the software. Change the mode drop-down to refresh the port list. 5. **Linux** : add your user to the `dialout` group. 6. **LED** : if the blue LED stays off, check the USB connection, power and firmware. A connection that depends on cable position points to a worn cable or damaged connector. Test on another computer to isolate the problem. Source: openQCM support archive (40 threads) ### The software connects but shows no data, 'emptybuffer', or stays on 'processing early data'. What is wrong? *Applies to: NEXT, Q-1, Wi2* - **Right program** : NEXT, Q-1 (also the Q-1 shield) and Wi2 (also the oscillator Teensy shield) each have their own software, and they are not interchangeable. The old Java program is for the first generation only. Q-1 software on a Wi2, for example, gives *emptybuffer* errors at calibration, because the device never sends sweep data. - **Firmware** matching the software version. - **Port and cable** : the correct COM port, no other program using it, a data cable. - **NEXT power** : both the data and the TEC power cable. - **Sequence** (Q-1/NEXT): calibrate first with the correct 5/10 MHz preset. "Processing early data" is normal for about 30 s after Start. If it never ends, or "convert raw to float failed" or "Ref. freq is not set" appears, the device is not sending valid data or the resonance is outside the window: check the above and recalibrate. - **Fresh copy** : re-extract the program (for example with 7-Zip), keeping the folder structure, and run the original executable, not a moved copy. - **Autoscale** the plot ("A" or *View All* ). If a serial monitor shows data, the problem is on the software side. Source: openQCM support archive (36 threads) ### How long can the connection between the crystal and the electronics be? *Applies to: all instruments* As short as possible. The crystal signal is in the MHz range: long or unshielded wires pick up interference and add capacitance after only a few centimetres. On oscillator boards this can stop the oscillator or make it lock onto a wrong frequency, with readings off by megahertz; on the Q-1 and NEXT it distorts the calibration scan and can cause failed peak detection. - Use shielded coaxial or shielded twisted cable with the shield grounded, and identical, matched lines for the two crystal connections. A short coaxial lead of a few tens of centimetres is workable. - Between a Q-1 or Wi2 sensor module and its main unit, use only a full USB 3.0 extension. A USB 2.0 cable lacks the extra conductors: frequency may work but the temperature reads zero. After wiring, check that the resonance is near the nominal frequency and that breathing gently on the crystal shifts it by only tens of hertz, recovering within seconds. Source: openQCM support archive (10 threads) ### How can I check quickly that my instrument and sensor respond correctly? *Applies to: all instruments* 1. Mount a **new, clean** crystal, calibrate (Q-1/NEXT) and record a baseline in air until it is stable near 5 or 10 MHz. 2. Breathe gently on the crystal: water vapour should give a temporary frequency drop that recovers within seconds. 3. On an open holder, place a 5–10 µL drop of water exactly at the centre of the large electrode. The frequency should drop clearly and settle. A drop reaching the edge can short the electrodes or stop an oscillator (0 Hz). 4. In a closed cell, fill with pure water and compare shift and noise with the device test report. Optionally alternate water and ethanol or isopropanol a few times (not with a PMMA window): the steps should repeat. If this works but your experiment does not reproduce, look for micro-bubbles, residues, surfaces that differ between runs, temperature differences, remounting between runs and interference. Run blank, sample and blank again in one continuous acquisition and compare relative shifts. Send support your data files and screenshots if needed. Source: openQCM support archive (14 threads) ### Why do crystals break when I close the cell? *Applies to: Q-1, Wi2, NEXT* Crystals usually break from uneven pressure: - the crystal is not centred, or sits tilted on the pins; - the pogo pins protrude too far above the support O-ring; - the cover is overtightened to stop a leak; - the cover is pressed by hand to remove bubbles; - liquid is pumped into an obstructed cell, creating overpressure. Make sure the crystal lies flat and centred before closing, set the pin height correctly, and fix leaks at their source (O-ring, window screws, lever or nuts) instead of applying force. Check that the channels are clear before pumping. 10 MHz crystals are thinner and more fragile than 5 MHz ones. If breakage continues with correct handling, contact support: the cell may have a mechanical tolerance problem. Source: openQCM support archive (2 threads) ### My Wi2 or other oscillator-based setup reads 0 Hz. Why? *Applies to: Wi2, Holder, TWIN, SpaceBug* On oscillator electronics (Wi2, Teensy shield with the Holder, TWIN, SpaceBug), 0 Hz or a constant out-of-range value means the crystal is not oscillating. Plain water should not stop it. Common causes: - no crystal, crystal upside down, poor or contaminated contacts, pins too low; - liquid behind the crystal or on the contact board after a leak; - too much damping: a thick, soft or swelling coating, a very viscous liquid, a large or off-centre drop touching both electrodes, or a much-reused crystal; - a cover pressing too hard, long cables, or a supply below 5 V. Test with a new bare crystal in air, then with a small drop centred on the large electrode. Going from air to water, expect roughly −0.7 kHz at 5 MHz and −2 kHz at 10 MHz. A brief zero that recovers points to a transient (a drop, a bubble, a loose contact); gaps in the data without zeros point to serial communication. For viscous samples, soft films or heavy loads, use the Q-1 or NEXT: they sweep the resonance passively, still follow a weak, broad peak and also report dissipation. Source: openQCM support archive (31 threads) ### I see a second peak close to the resonance at a higher overtone. Is the crystal defective? *Applies to: NEXT, Q-1* Spurious (anharmonic) modes normally appear above the main resonance and spread over a range wider than the sweep window. A second peak just a few kilohertz from an overtone resonance that stays with the crystal when you clean it, remount it or change instrument points to a defect in that crystal, for example non-uniform electrode deposition. Check several crystals from the same batch on the same instrument and keep screenshots. If the main peak is distorted so that tracking fails, use another sensor or another overtone. Report affected crystals to support with the batch information: they can test and select replacements, including checks at a specific overtone before shipment if your work depends on it. Source: openQCM support archive (1 thread) ### My older Wi2 has the Wi-Fi module. Why does the web chart stay empty? *Applies to: Wi2* (Legacy: earlier Wi2 units fitted with the discontinued ESP8266 Wi-Fi module. Current Wi2 units are USB-powered and have no built-in wireless.) - Power the Wi2 through its main micro-USB socket; the module's own USB socket is for programming only. - First join the module's own network (access-point mode) to enter your local network credentials, then join your local network and open the IP address shown, where the live chart appears. - An empty chart can mean the module receives no data from the main microcontroller; check its serial output with a serial monitor. On one firmware generation the web page also loaded its charting library from the internet. Firmware updates fixed both problems. - On offline PCs you may need the CP2104 USB-serial driver to program the module. Contact support for the firmware matching your unit. Source: openQCM support archive (3 threads) --- openQCM by Novaetech S.r.l., Pompeii, Italy · Buy: https://store.openqcm.com/ · Contact: info@openqcm.com · https://openqcm.com/contacts/