Archive for May 21st, 2011

DIY :: Geiger counter with USB connection, part II

Here’s the finished board connected to my computer. It works surprisingly well, reading about 20CPM on average — it might be cosmic rays or anything, because I’m too far from Fukushima and don’t really believe anything can be brought over here by wind. The power consumption from the USB bus is less than 10mA, which makes it safe to connect to any USB port, even to a laptop/notebook with a small and weak battery.

But even with this low power consumption, the naked board does not play quite well with bare hands — it still has enough voltage (about 400v) inside and is always ready to zap the finger. Still, the discharge current is very low — about 10uA, so it’s just a bit more annoying than static electricity discharge, like the one you get while getting off the sweater.

And here’s a fresh plot of today’s data. I have no idea what happened between 17:00 and 20:00, maybe my neighbours were microwaving the sausage or we had a solar flare, because it does not look like radiation at all. The radiation usually builds up pretty fast and then slowly decays over time, not the opposite, as seen on the picture. I shall check tomorrow’s graph to see if this phenomena will repeat itself again tomorrow.