Hi & a question about CPM

Simomax wrote:

What everyone else said. There is a small chance it could be interference from something electrical. Cheap nasty Chinese switch mode power supplies can often emit noise. Make sure you have a decent PSU running your Pi and counter. As an example, running a plasma ball near a Geiger counter will make it go crazy!

As mw0uzo mentions, leave it running for a few days to see if there is a pattern of it counting higher at nights. Also, do you any kind of check source such as Uranium glass, fiestaware pottery (Uranium glaze) or something else you could use? If so then place it right at the tube to get the highest count then slowly move it away from the tube. If you see the counts going down steadily as it gets further away the tube voltage is probably set OK. If the counts stay high then drop in sort of chunks then the voltage may be too high causing the tube to avalanche. Don't rely on the CPM display though as this takes ~30 seconds to settle. Instead listen to the clicks it makes.

I Have just had a look at the kit. Make sure the jumper is removed for correct 400v. With the jumper fitted it will be set to 500v which is too much for the SBM-20 tube. Also if this was a kit you have built then check that the correct 10M ohm resistor is correct and not mixed up with another value resistor.

If all seems well then jet it run a few days and we can have a look at the data. Times/counts etc. There is a possibility this was an event, though at 70CPM it's nothing to worry about if it has come and gone. I have had a couple of times when it has rained hard and my counts have gone up due to the rain trapping radioactive particles in the air and bringing them down to ground level.

Don't worry about it though. There are a lot of clever people on this site so we'll get you up and running properly

Simomax wrote:

I'm also surprised there is no circuit diagram with the kit. IMHO there should be!

docsquee wrote:

Thanks, Alpha01. I've check the voltage and it's sat around 400V (380V +).

docsquee wrote:

I'll compare using shorter wiring to the tube from the PCB and see if that helps steady counts in the future.