The Geiger–Müller counter, also known as a Geiger counter, is an instrument used for measuring ionizing radiation. According to Wikipedia, the device detects radiation such as alpha particles, beta particles and gamma rays using the ionization produced in a Geiger–Müller tube.
“Lately I have been messing around a bit with microprocessor powered geiger counters. One smart guy came up with the idea of generating high voltage using PWM signals from the microprocessor itself,” Johan explained in a detailed blog post.
“With some additional external parts a HV supply and negative going pulse suitable for microprocessors is easy to make.”
So, how does the circuit work? Simply put, a ~1 Khz squarewave turns the MPSA44 high voltage transistor on and off – generating high voltage when the inductors current is shut off.
As Johan notes, the specific voltage is contingent upon the pulse width of the square wave which can be tweaked on a software level.
“The 1N4007 diode rectifies this voltage, and the HV cap removes most of the ripple on this voltage. The resistor limits current to the GM tube,” he continued. “The current pulses from the tube generate a voltage drop over the 100K resistor which turns on the BC546. When this happens, the voltage [via] the 10K resistor is pulled to ground, generating a negative going pulse each time the GM tube detects an ionizing ray or particle.”
It should also be noted that Johan’s design supports serial logging capability using a tx only software serial library tasked with outputting the measurements in CPM every 10 seconds on pin 4.
So, what’s next for the Trinket-powered geiger counter? Well, Johan says the platform still requires some tweaking, as the circuit is quite susceptible to electromagnetic interference which causes erroneous counts.
Interested in learning more? You can check out the project’s official page here.