A while ago, I decided to build my own Geiger-Müller counter to be able to measure radioactivity myself. After Fukushima, all reasonable priced counters were sold out, so I’ve decided to build mine based on a Velleman Kit. (K2645)
The kit is pretty easy to build, but it doesn’t really offer much – it just beeps for the gamma or beta decay. To get an idea about the actual exposure to radioactivity, we need to count those beeps over a defined period of time.
I’m using a 555 to clean and convert that single beep into a pulse that can be counted and detected by a PIC (16F684) microcontroller. The PIC counts those pulses and calculates the radioactivity dose in micro sievert. I calculate the dose for the last minute, plus average over a longer period. The example in the picture shows 0.17 uSv per hour which is reasonable in the region Basel/Switzerland.
As an added bonus, the PIC also measures the voltage of the 9V battery.