# openQCM TWIN

> Source page: https://openqcm.com/about-openqcm-twin
> 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

_OEM board · differential QCM · gas and vacuum_

openQCM TWIN carries two identical oscillators on one OEM board. One crystal meets your gas or your vacuum; the other stays behind as a reference, under the same conditions. Whatever moves both, temperature first of all, cancels in the difference. Whatever moves only the sensor is your signal.

## Key figures

- 2: crystals: sensor and reference
- 1–25 MHz: frequency range
- ±1.5 A: Peltier drive
- ~25 g: board weight

## Differential: Two oscillators, one difference.

Two Pierce oscillators on SN74LVC1GX04 inverters, with identical components, drive the sensor and the reference crystal through gold-plated MMCX connectors. A Teensy 4.0 counts both in hardware over 2 ms gates, accumulated into a one-second window, and reports the two frequencies and their difference. The difference also leaves the board as a TTL signal on its own connector, for a counter or a data logger.

## Thermal control: And a Peltier to hold still.

A Thorlabs MTD415T controller drives a thermoelectric element up to ±1.5 A, heating or cooling, reading a 10 kΩ thermistor with better than 10 mK resolution (2 mK typical). Its digital PID, with auto-tuning, holds the setpoint to 100 mK typical. An MCP9808 sensor (±0.25 °C) watches the board, and a PWM fan output completes the loop.

## Integration: Made to disappear into your rig.

TWIN mounts on four M2 screws and takes your own sensor holder, Peltier, thermistor and fan on push-wire terminal blocks. In the box: the board with a Teensy 4.0 and sample firmware, USB data cable, USB power cable and 5 V adaptor for the Peltier, five SMA-to-MMCX cables and a sample Peltier-thermistor kit.

## Firmware: Plain text on a serial port.

The open Arduino firmware prints one line per second: F with reference frequency, sensor frequency and their difference in hertz; T with the Peltier temperature; C with the board temperature. Anything typed on the port goes straight to the MTD415T, so the temperature controller can be tuned from a terminal.

## Honest limits: Where the board ends.

TWIN measures frequency at the fundamental only. Its manual gives no frequency-noise figure and no vacuum rating for the board itself: in a vacuum system, the crystals sit in your holder and the board stays outside, behind a feedthrough.

## Specifications

### Measurement

- **Crystals:** 2: sensor and reference
- **Range:** 1–25 MHz
- **Quantity:** Frequency, at the fundamental
- **Oscillators:** 2 × Pierce, SN74LVC1GX04
- **Counting:** Teensy 4.0 timers, 2 ms gates × 500 = 1 s
- **Outputs:** USB serial (115200 baud); TTL difference frequency

### Thermal

- **Controller:** Thorlabs MTD415T
- **Drive:** ±1.5 A at 4 V, heating and cooling
- **Sensor:** 10 kΩ NTC thermistor, resolution < 10 mK (2 mK typical)
- **Stability:** 100 mK typical (digital PID, auto-tune)
- **Board sensor:** MCP9808, ±0.25 °C typical
- **Fan:** PWM output with RPM line

### Board

- **Size:** 59.8 × 53.5 mm
- **Weight:** ~25 g
- **Mounting:** 4 × M2 holes
- **RF connectors:** MMCX: SENS IN/OUT, REF IN/OUT, TTL difference
- **Power:** USB 5 V (logic); 5 V jack (Peltier)

## Buy or ask

- Store: https://store.openqcm.com/
- Contact: https://openqcm.com/contacts/

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openQCM by Novaetech S.r.l., Pompeii, Italy · Buy: https://store.openqcm.com/ · Contact: info@openqcm.com · https://openqcm.com/contacts/