# openQCM Holder

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

_Sensor holder · all FR-4 · from the bench to vacuum_

openQCM Holder has no case. Three layers of FR-4, the glass-epoxy of circuit boards, are at once the structure, the crystal seat and the wiring. Under 5 grams and 4 mm thin, with no plastic housing, it carries a QCM crystal from the open bench into a vacuum chamber.

## Key figures

- < 5 g: weight
- 4 mm: thickness
- 25 × 18.6 mm: without the plug
- 1–10 MHz: crystals, 14 mm

## Three layers: Electronics as structure.

Three FR-4 layers clamp a 14 mm wrapped-electrode crystal (1 to 10 MHz) and carry its contacts, an MCP9808 temperature sensor on I²C (−40 to +125 °C) and a Pierce oscillator whose output is a TTL signal at the crystal's resonance frequency. Building the holder from circuit board removes the plastic housing, and with it a source of mechanical play.

## Two ways to connect: A plug, or seven gold pads.

The USB version plugs into your own acquisition electronics through a USB 3.0 connector with its own pinout. The pad version is made for soldering: seven gold pads take the wires of a vacuum feedthrough, so only the holder sits inside the chamber.

## Warning: It is not a USB device.

Never plug the USB version into a computer. The connector is a USB 3.0 plug, but its pins carry the crystal, the oscillator output and the I²C bus, not USB: a standard port can damage the holder.

## Vacuum: What the manual says, and what it does not.

All-FR-4 construction makes the holder suitable for atmospheric and vacuum environments. The manual gives no pressure range, outgassing figure or bake-out temperature: check them for your process, and keep the rest of the electronics outside the chamber.

## Specifications

### Sensor

- **Crystal:** Single, 1–10 MHz, 14 mm, wrapped electrode
- **Electronics:** Pierce oscillator, TTL output
- **Quantity:** Frequency
- **Temperature:** MCP9808 on I²C, −40 to +125 °C

### Mechanics

- **Material:** FR-4, three PCB layers
- **Size:** 25 × 18.6 × 4 mm; 40.2 mm long with the plug
- **Weight:** < 5 g

### Electrical

- **Connection:** USB 3.0 plug (custom pinout) or gold solder pads
- **Supply:** 3.3–5 V
- **Current:** Max 80 mA at 5 V

## 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/