I wanted to trigger an external camera with this detector so events involving the simultaneous discharge of the GM tubes (eg. a muon passing through) can be captured in a cloud chamber. I didn't have a camera that can be triggered that way (although there are a few like that on the market), so I connected a small computer to the detector with a camera attached to it.
This involved some programming, too. I rewrote the GM code I made earlier. I didn't have a cloud chamber handy, but tested the electronics and it seems to work as intended. The camera is triggered through the Raspberry Pi with hopefully not too big delay for the track to be still visible in the chamber. I connected a webcam first and thought that would be fairly trivial, but I found out that the Raspberry Pi (this was a 2) didn't really like webcams. I had to write a shell script to check the status of the webcam and restart the SMSC ethernet/USB chip on board the RPi occasionally. It's a pity that the network goes with the USB, too. So, ifdown, restart the chip, ifup... That made it work reliably. I'm going to try it with the dedicated RPi camera, that should give better results.
Here's a picture of the boxed prototype. There's a video further down about the making.
Operating voltage: 3 V through the main connector.
Could be operated at 5V on the ISP header only when programming the on board microcontroller. The main connector is NOT 5V tolerant.
Power consumption: 27 mW (typical with 2 GM tubes connected @ background radiation)
Coincidence times: 5 micro second (typical). Range is 2 - 8 us.
Maximum count rate: 5000 counts per second when using SBM 20 tubes.
Current: 9 mA (typical).
Output voltage: 100 - 600 V adjustable, unregulated to be used with GM tubes only.
Series resistance on the high voltage connectors: 4.7 MOhm.
Worst case short current at the HV pins: ~0.1 mA.
Connectors rated at 1000 V (ac/dc).