Further experiments & improvements to the Arduino Geiger Counter

My dad recently returned from a small socially-distant holiday to Cornwall.

"I've bought you a gift, saw this and thought you'd like it!"
"The chap in the shop said it might be a bit radioactive" *

It's a "Radio Compass" from an aircraft. This is used to display a heading to a terrestrial radio beacon. This one's old. Old enough to have a Radium-266 dial. Waving the geiger counter near it proves the point, end-stopping the meter on both the SBM-19 and SBM-20 tubes. It does show a potential limitation in my counter though.. let's investigate....

The original project is here

The count rate appears to be being limited to a shade less than 1000 CPM. by something. It could be the tubes are saturated. It could the arduino is not capable of counting that quickly. It could be the high voltage supply is incapable of delivering that amount of current when the tube is at a high pulse rate, and the HT is falling between counts.

After poking round the high voltage supply, I think we can conclude it's not that ... 

There IS a delay in the tick function of the sketch, and also digitalWrite is notoriously slow.

After modifying the sketch , there's no detectable change, even with that delay removed, which IS still blocking the sketch. 

Looking closer on how I can get the loop to run faster, I'm unnecessarily updating the LCD every cycle, and reading the battery every 5mS ...

 ... this is moved into a non blocking loop counter, to update every ~3 seconds or so ..  

Oh that's fixed it ! I'm now getting a reading of ~30,000 CPM maximum from my radium dial... 

I also needed to tweak the meter movement routine a shade to compensate for the faster loop speed.

The new sketch can be found on my git as usual https://github.com/andydoswell/geiger_counter

*The chap in the shop also told my dad the chap he bought it from had a stack of them under his bed... I'd hate to see what his dose rate is like!