openQCM Wi2 is the frequency QCM in its plainest form: a Pierce oscillator keeps the crystal ringing, a microcontroller counts its cycles for one second, and that count is the measurement. Small enough for one hand, simple enough for a classroom, open down to the last screw.
Δf 0 HzSauerbrey 4.42 ng·cm⁻² per Hz
A Pierce oscillator built on an SN74LVC1GX04 inverter locks onto the crystal's fundamental resonance and follows it on its own. The microcontroller counts the edges of that signal over a fixed gate, typically one second. What comes out is the resonance frequency, with the crystal temperature from an MCP9808 sensor pressed against it. Wi2 measures frequency only, at the fundamental: for dissipation and overtones, see Q-1 and NEXT.
The 14 mm wrapped-electrode crystal rests on two pogo pins, contact side down. A lever sets the O-ring pressure finely, and a small magnet keeps the temperature sensor against the crystal. The cell holds about 50 µl; its only wetted parts are the window (PMMA or PTFE) and an FKM (Viton) O-ring.
The case is eight SLS-printed nylon PA2200 parts and a CNC-cut window; the main board is a two-layer 59.9 × 36.8 mm PCB with a Teensy microcontroller. The 45-page assembly manual goes through every step, from cutting the O-ring that cradles the crystal to the final leak test.
Power and data travel on one micro-USB cable at 5 V. Expansion headers on the board take a Wi-Fi module or a PCB of your own: Wi2 is wireless-ready rather than wireless out of the box. The software tells devices apart by their port, so several Wi2 can run on one computer, a whole bench of them in a teaching lab.
Each assembled unit is tested with a 10 MHz AT-cut crystal, at least 30 minutes in air and 35 minutes in static deionized water, in a 20–30 °C room. Acceptance: frequency standard deviation ≤ 1.0 Hz in air and ≤ 1.5 Hz in liquid, crystal temperature stable within ±0.1 °C, equilibrium in about 10 minutes in air and 20 in liquid.
| Acceptance test, 10 MHz crystal | Air | Static liquid |
|---|---|---|
| Frequency standard deviation | ≤ 1.0 Hz | ≤ 1.5 Hz |
| Crystal temperature stability | ± 0.1 °C | ± 0.1 °C |
| Typical equilibrium time | ~10 min | ~20 min |
| Room temperature | 20–30 °C | 20–30 °C |
From the official manual. Where two documents disagree, the figure is left out until it is confirmed.
Recent publications where the Wi2 was the measuring instrument, from the openQCM bibliography.
Woranan Netkueakul, Savvina Chortarea, Kornphimol Kulthong, Hao Li, Guangyu Qiu, Milijana Jović, Sabyasachi Gaan, Yvette Hannig, Tina Buerki‐Thurnherr, Peter Wick, Jing Wang
Read at the publisherTomasz Wasilewski, Damian Neubauer, Marek Wojciechowski, Bartosz Szulczyński, Jacek Gębicki, Wojciech Kamysz
Read at the publisherDário José Costa Junior, Jaime Francisco Ribeiro Hamann, Lucas Akio Yoshioka
Read the publicationWi2 ships from Pompeii, Italy, ready to measure, or build it yourself from the open files.
Explore. Measure.
Publish. Repeat.
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