Check out the video to see what I mean.
From a technical point of view this project has a few interesting aspects.
- Interfacing a custom circuit with an existing circuit board
- Capacitive touch controls
- 7-segment LED display
- Customising microcontroller software
It's only been roughly calibrated. But the circuit is robust enough to be pretty accurate with proper calibration and perhaps some tweaks to the software.
Step 1: Materials and Tools
- This DIY geiger counter. It's not cheating. There is no point reinventing the wheel! This is a great circuit, already tested and works very well. What is really useful is that it incorporates an ATMega328 microcontroller (it has an Arduino built in). I will be running my own customised code on it.
- A Geiger–Müller tube. This is the sensor that actually detects radioactive particles. These can bought on ebay. I recommend either an SBM-20 or SI-180G. They are especially sensitive to gamma rays and are relatively cheap. In fact, for this project I used one of each in parallel.
- Project box. A nice box to hold everything makes a big difference. I used the biggest size of this. It is the biggest one I could find at a reasonable price that looked alright. It was a wee bit small though and required a bit of creativity to fit everything in!
- 2mm clear acrylic sheet. Often known as perspex this is the "screen" of the geiger counter. The touch switches are hidden underneath.
- Overhead projector transparency sheets. The interface graphics are printed on this and then laminated to the acrylic. I also use these for the method I use to make the circuit board.
- Electronic components
- 5mm LEDs: 9x red, 4x white
- Resistors: 2x 82Ohm, 1x 100Ohm, 5x 220Ohm, 1x 6.8kOhm, 1x 22kOhm, and 4x 10MOhm
- 1x 10kOhm trimpot
- PCB single row headers (male and female)
- 1x Maxim MAX7219 LED display driver
- 2x 4 digit 7 segment LED display (common cathode, 0.36")
- 1x slide switch. This is the only mechanical switch used to turn the device on. I salvaged mine from an old digital photo frame as it had a nice cap on it.
- 1x 9v battery and holder
- thin single core wire to use as jumpers on the circuit board.
- general purpose wire for connecting geiger tube and battery to circuit
- 2x PCB mount screw terminals (for power)
- fuse holder (to attach to geiger tube terminals)
- dual-layer blank PCB for our circuit board
- single-layer blank PCB to make touch sensors
- 1x 0.1u capacitor
- 1x 24 pin IC socket