My latest project -
Attached FileIt's built around
this kit and a couple surplus Soviet Geiger tubes (one for low-level measurements, and one for oh-shit-we're-all-gonna-die measurements) - all packaged inside a Hammond die-cast aluminum case.
One of the neat things about this kit is that not only is it capable of displaying instantaneous radiation levels and calculated dosage rate (32 counts per minute and 0.02 mR/hr in the above picture), it also has a second display page that can show long-term averages:
Attached File(In this case, it's displaying a 1-minute average of 16 counts per minute and 0.01 mR/hr, and a 60-minute average with the same values).
The 60-minute average is probably the most useful for monitoring background radiation levels over the long term - In my location with my particular Soviet SBM20 Geiger tube, it's always 16-18 CPM, no matter what.
This contrasts with shorter average intervals, which randomly vary quite a bit from moment to moment.
There are also programmable setpoints for CPM and mR/Hr that will sound an alarm if they are exceeded.
The remote control allows various parameters to be user-adjusted - I added a switch to disable the IR receiver when the remote isn't being used.
With the backlight turned on, the unit only draws about 25 mA at 5 volts - so it'll run for several days on a $5 Wal-Mart rechargeable USB power pack (shown attached to the back of the unit):
Attached FileSmall magnets secure the power pack to the unit, allowing it to be easily removed when not in use:
Attached FileNormally, it sits on my workbench without a battery pack attached, running 24/7, powered by a USB wall wart.
Total parts cost: $110, maybe?