Mighty Ohm Geiger Counter Build

31 Dec 2015 - Nic Ho Chee

I've been meaning to solder up the Mighty Ohm Geiger Counter Kit for a while. It was sitting on my desk forlorn and unused, and I had a couple of hours free just before Christmas to try it out.

A few hours later the kit was blipping along nicely, with a few observations from my very brief interaction with it:

• When tired don't move your soldering iron from your right to your left hand... because you'll end up grabbing the burning fire stick by the hot end. Ouch.
• Listening to the sound of background radiation hitting a geiger counter you've just put together is surprisingly scary. Random ionising radiation FTW!
• Granite is a much lighter beta/gamma source than I was expecting.
• If you're debugging the unit with a Multimeter, the GND pin of the Pulse pins (J6) is a good ground point to check voltages. I was using this to check against TP2 to understand what the voltage was going across the left hand side of the circuit, debugging the ICs etc. The GND pin is the top most pin of the three as you look at the circuit with the battery unit topmost.
• Check the direction of the ICs. I had a bug in the circuit caused by putting IC U2 into the unit back to front. The holder was soldered in correctly, but I'd parsed "Make sure the notch..." as, "line up the large circle with Pin 1 of the IC holder" which was completely incorrect.
• The tracks and pads are really great in the kit, but be careful when mounting the battery holder. It was the only thing that I had a problem with when I was soldering it. You need a smaller tip, and make sure that you get enough heat into both the leg and the pad to get the solder to flow correctly.
• Be careful about the quality of the batteries you're using. I had some rather dubious AAA batteries initially and they became quite warm when I mounted U2 upside down. The battery drain looks like it could be quite high in this case. I didn't have the same problem with the Duracell Plus Power AAAs that I ended up using rather than the dodgy generic versions I threw away.

I'll be spending a little more time with the unit once I can get hold of a USB -> Serial port, and will put some code up on github somewhere once I have something to try out :).

It is worth following @mightyohm, the creator of the kit and his blog over at mightyohm.com. There is some great stuff there, including the Soldering Is Easy comic book :).