Geiger counter from recycled stuff

When fiddling around with smoke alarms containing radioactive isotopes I got interested in measuring radioactivity in general. A friend gave me a FZH76V Geiger-Müller tube that require 500V exitation voltage. Most discarded LCD monitor has a high voltage driver for the backlight VFD tubes. Normally these drivers run on 12V and produces a couple of kV but when run on 5V they easily provide the around 500V that a typical GM tube require.
The above circuit can be connected directly to a micro controller and the pulses it generates can easily be picked up on a normal I/O pin.
I have only tested the circuit with the FZH76V tube but i’m sure that it can be adapted to other devices. I know from experience that the exitation voltage need to be within 10% of the specified value for the device for things to work well.

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