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Low Cost Geiger Counter

I wanted to build an X-ray machine. Not really knowing a ton about x-ray machine design, I decided to dip my toe into the pool of high voltage and dangerous devices with a Geiger counter.

I started with the HV power supply. I’m using a SBM-20 tube, and need around 400V across the tube for proper operation. However, it needs a few uA a best, making the design fairly trivial. I opted to use a boost converter, although if I was going to build more than one, I’d probably move to a transformer. It’s a basic boost design, with a 10uH inductor, UF4007 diode, high voltage BJT, and a switching frequency generated by the Arduino – it’s somewhere around 10kHz. This is then sent to the filter capacitor, a metalized film cap rated for 800V, and through a resistor to the anode of the tube. Whenever a particle of ionizing radiation hits the tube, it triggers a breakdown, causing a sag in voltage, which is picked up by the Arduino and registered as a count.

Past that, it’s a simple serial output. In the future, I’ll add a better feedback mechanism, better filtering, a more robust power supply,an LCD interface, and a case so I can stop zapping myself all the damn time.

Realistically, I’ll just re-design the thing. However, barring nuclear holocaust, it’s not of much practical purpose. Maybe I’ll knock it out over the summer.