I “rebuild” my Geiger counter, the SBM-20 tube was initially inside the box, so, i have put this one inside a 32mm diam plastic tube, for more convenience, wired through a XLR3 cable.
The LCD display alternatively, the “count per minutes” and result on: milli Sievert/year or nano Sievert/hour, you can switch off/on the buzzer, also 3 modes on measure are available, 15/30/120 secs.
This counter is from “Electronique-Pratique” n°368, a French electronic magazine. Shem, pcb, and PIC hex & C source code available. (Microchip compiler C18 v2.40/MPLAB 8.4)