MarkusB of Lets Make robots designed this simple Geiger counter. If you’ve somehow come across a Geiger counter tube and want to make a detector out of it, this could be just the thing you need. His design uses only commonly available parts, and is powered by a 5v power supply. He plans to make a radiation-seeking robot out of it, perhaps as an atomic version to Natalie Jeremijenko’s feral robotic dogs?
This is all well and good, but how does the circuit work? Let’s take a look:
Looking at the circuit, it basically breaks down into three parts: On the far left, a 555 timer is configured in an astable mode, causing it to generate a square wave at some frequency. This square wave is then fed into a charge pump, creating a (claimed) 300-1000v potential, which is used to power the Geiger counter tube. When a particle or photon of radiation moves through the tube, it allows the inert gas in the tube to conduct electricity (source: Wikipedia), allowing some charge to flow from the high-voltage lead of the tube to the other side. This causes the on the sensing lead to go up for a short amount of time, which then causes a second 555 timer to put out a short pulse.
Note that I haven’t simulated this circuit, so I don’t know if it actually works with the specific components specified, however the general topology (layout) appears to be correct. Have you designed or built a similar circuit for a geiger counter? Have any suggestions to improve this one?