simple geiger counter circuit

Super simple 555 GEiger Mueller Driver circuit

Recently someone asked if it was possible to build a cheap GM-Driver circuit which is a HV source and a pulse output connected to a speaker. When a gamma/beta/x-ray is detected by the tube, the unit will make a click noise.

I’ve decided to make one only by using very standard parts everyone should be able to obtain. To be honestly, I have already built one of those some years ago but have not really documented it properly. The unit still works fine with all the parts shown below.

Schematic 1: Principal of a super simple step up GM Driver

When the MOSFET Q1 shuts the current through L1 off, a current pulse rushes through D1 which is a standard 1000V rectifier diode. The current charges C2, a high voltage rated 100nF foil capacitor. When the set voltage is reached the Z-diodes regulate it to their limit. The voltage can be lowered by just shorting one or multiple Z-diodes out. In the given case, the voltage will stay at 400V. The diodes should be chosen with a reverse saturation current as low as possible to lower the idle power consumption to a minimum. The current to charge the GM-Tube MUST be limited by a 7-15M resistor R1. When a ionization is detected the GM Tube discharges through R2 into the base of a BC547B NPN transistor. The transistor lets current flow and pulls the pulse output low for a very short time. It is important NOT to use a FET as Q2 as it will be easily be destroyed when the HV builds up at the gate.

The PWM drive for Q1 and the pulse-out-detector which drives an active buzzer can be both made by using a 555 type timer IC.

Coming soon: Schematic for GM Driver with 555 timer ICs and Schematic for GM Driver just using one AtTiny microcontroller. Edit: March 24 2022, I have had many other projects since and have not forgotten about this one, there will be an update. Also check out my other projects.

This is a work in progress…