A Geiger Counter is perhaps the ultimate geek toy, but the price of commercial devices such as the Gamma Scout have always been too high for me. Recently prices have been coming down as Fukushima mania subsides and sellers dump excess stock. A number of DIY kits have also appeared, tying in with the Raspberry Pi and Arduino market.

Enter RH Electronics “My Geiger”, a ~$50 DIY Geiger counter kit. This is an Arduino compatible PIC16F876A based device with graphic LCD and TTL serial output for data logging.

The kit can be ordered either unassembled or (mostly) assembled. I chose the assembled option as it does not add much cost. The package arrived just over a week later (priority mail from Israel). No instructions are included in the box but a link to the website provides a PDF manual. Even with the assembled version a small amount of soldering is required - three switches and an (optional) LED, but this is very basic stuff. You’ll also need to make an enclosure, for this a Dremel tool or similar is needed to cut holes for the LCD/switches/USB port.

The quality of the PCB and soldering is high.

The tube clips are designed to accommodate an SBM-20 or STS-5 Geiger–Müller tube, although any 400V tube can be used. I went with the slightly cheaper STS-5 from Ukrainian seller “any-devices” on Ebay.

Power and connection options are numerous: USB TTL - power (5v) and data USB (type B) - power only - but data is possible by soldering TTL module RX/TX to USB socket. NiMH batteries: 4.8v (4xAA) LiPo: 3.7v 5V DC adapter Other output options are Arduino (interrupts via ARD pin) and Geiger bot

Input voltage range is given as 3.7V - 5.5V. Stated minimum battery capacity is 1000 mAh, but 4xAAA 850 mAh works fine for me.

TTL serial output. The CPM figure is output every 10s.

The heart of the device is an 8-bit PIC16F876A MCU. The display output consists of CPM figure (10s moving average) with meter, dose reading in (micro)sieverts per hour (needs calibration to have any meaning - and the firmware allows this) and tube voltage. The firmware is closed source and no binaries are available, so no customisation is possible. External controls are only three buttons and a power switch. The buttons are speaker on/off, backlight on, and the top button is to enter calibration mode. Power switch is for USB or battery, it has no effect when TTL 5V is used.

Maximum reading is given as 500000 CPM. Luckily, I don’t have a source that will get anywhere near this. The highest count I have seen is from “fiesta ware” fragments held directly next to the tube: ~7000 CPM vs background here in south west England of ~20 CPM. An ionisation smoke detector gives readings of ~70 CPM externally.

Overall I’m pleased with the RH Electronics MyGeiger. I now have a fully functioning Geiger counter at half the price of even the cheapest commercial devices. My only complaint is that the firmware is proprietary. This is definitely a negative compared to similar kits, so I hope they will consider releasing the firmware at some point.

[youtube http://www.youtube.com/watch?v=mphglGKLTtI&w=560&h=315] Testing device with uranium glazed pottery.