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I assembled my geiger counter, and was happy to see it working right away. I was pleased to see that it worked immediately, and that I could leave the pot at its leftmost setting. However, now I'm a little worried. I get about 25 CPM, but a fair few of them are very quick double clicks or triple clicks in quick succession - is this normal behaviour, or is it possible I've stuffed something up and have too greater a voltage being fed into the tube?

In particular I want to know this because I read elsewhere that you can power the geiger counter using the 3.3v output of an Arduino to the 3rd pin of the J6 pulse header. If I did this, is there any chance I could damage anything (assuming I remove the batteries).

Thanks for your time - and thanks for the project. I put it together without really knowing much about electronics - and I'm really happy with it.

Double and triple clicks, if they are happening often, may be indicative of an intermittent connection, a voltage out of range, or a failing geiger tube. Did you purchase the tube with the kit? I test all tubes before I send them out, but sometimes they fail in transit (does the tube rattle?)

Try inspecting and reflowing any suspect solder joints, and try varying VR1 to see if that makes any difference.

3.3V should work without modifications as this is very close to the design voltage of 3V (2xAA batteries).
Be sure the batteries are removed to avoid any chance of inadvertently charging them (very bad for alkaline cells!)

Thanks for your reply. I'm using the tube that came with the package. I gave it a shake, but heard no rattling. It is possible, I supposed, it could have been damaged in transit as I live in Melbourne.

Anyway, the next thing I tried was increasing the voltage using the blue pot. As I said, my counter clicks even on the lowest setting, but I slowly increased it to about 1/3 of the full range. The double and triple clicks were much reduced - or rather, most of those that remained no longer sounded so rapid fire in succession anyway.

I was thinking I could buy another SBM-20 tube to check whether it is the tube or my soldering that is the problem. Would one of these be ok?
http://www.ebay.com.au/itm/TESTED-SBM-2 ... 19fab1f736

Thanks for getting back to me.

Yes, that is the right tube. I will also replace any tubes that arrive faulty. PM me your address and order information.