One problematic issue was sourcing the proper detector, one that was both sensitive and small to fit the tiny space available in the already feature-crowded new uRADMonitor variant. After a slow process and intense communication with radiation detector manufacturers, we finally found a good candidate, putting price and performance in a reasonable balance: LND Inc and their excellent LND712 end window Mica Geiger tube.
To give it a quick test, the tube was hooked to one of the model A boards, and the voltage configured in software from 380V (which is used the SBM-20 and SI-29BG tubes) to 500V! Yes, the model A hardware supports that just fine with no other changes than a single constant changed in code, thanks to the excellent high voltage inverter circuit:
The result was as expected, and can be seen in the second image. The voltage on tube measurement is presented, part of the internal inverter feedback mechanism, responsible for having a regulated output matching the target voltage, in this case exactly 500V.
Compared to the SBM-20, the LND712 shows the same sensitivity at a smaller size.
But the Alpha and beta radiation sensitivity is the plus we’re after , and we get that just fine thanks to the mica end window.
The BOM production cost, however, will inevitably increase, as a single LND712 gets close to $70, the tube only and this is just a little fraction of all the components that need to go in the new model D environmental dosimeter.