This is my solo debut as part of the element14 Presents team, and I’m extremely excited to be on this journey.
Matt Eargle is a cold war nut who loves historical technologies. He just happens to have some old Soviet surplus Geiger tube sitting around. He’ll use it to build his own take on a Geiger counter. It will be something like an updated CDV 700 series. The original CDV-700 Series models were in production from 1954 until 1974. Later XXX series models were produced well into the 1980s. In order to build a homebrew version of a Geiger counter, he’ll need a couple of components in addition to his Geiger tube. A Geiger tube has a sealed vial inside a sealed glass tube containing an inert gas. You take that and apply a really high potential, the one he’s using is about 400 volts. When your particle comes in and strikes the nucleus of the gas inside, it temporarily ionizes that gas, just enough to allow some of that voltage through that it can be measured.
He’ll need a high voltage source to feed his tube. The cathode of the tube will run into an Arduino. Running the high voltage source through batteries will require a transformer. The transformer will require an AC current. The easiest way to create an AC current would be to create a little oscillator with 555 timers and run that into an inductor. The 555 timer will set up in astable mode to produce an alternating signal at 60 Hz that will get amplified by a MOSFET before running into the transformer. The current from the transformer will go into a diode laddering system which will drive the GM tube. The signal from the Geiger tube will run into an NPN transistor. The output pulse of the tube is around 200V, so it needs to have some level of conditioning before it can be counted by the Arduino. Once the output is run into ground they’ll have a digital signal that they can feed back into the Arduino.
He tests the circuit in a breadboard to make sure it works. The output of the Geiger tube is hooked into an oscilloscope. Matt uses an old aircraft instrument, an ADF with a glow in-the-dark radium dial to test to ensure that a signal is outputted to the scope. Now that we know the signal is working, we can condition that signal to create a digital pulse that we can measure and count with the Arduino. The tube output runs through a voltage divider so that it doesn’t fry the transistor. All that’s left is to 3D print some parts and do some coding using the Arduino IDE.