Open ThomasWaldmann opened 4 years ago
answering my z-diodes in series question:
Idea:
Currently, 2x 200V Z-Diodes are used to define a fixed 400V "full" voltage.
Use 3 places on the PCB (future PCB revision) for Z-diodes.
With the current PCB revision, this can also be done, just a little less pretty.
Hmm, anode resistors also need to adapt.
I asked Jürgen: We think, the LND712 could be used.
I tried searching some Z-Ds on mouser.com, but the huge amount of choices is confusing...
What are the design criteria to select for? Guess <= 500mW, zener current = ?, tolerance = ?, price, through hole, ...?
Z-Dioden z.B. BZX85C200, die kleine mit 3V3 ist ziemlich beliebig.
Yes, sounds like a good idea. There should be space left for one additional diode.
See also #86 - it seems the LND712 somehow works (although I am not sure about whether the CPMs seen are as they should be - it's hard to compare with the bigger / different tubes and also I do not have a conversion factor yet for the LND712).
After a long idle time for the LND712, I pulled that out again, flashed current firmware and it works!
It uses the standard PCB and parts, just with 1 addtl. 100V Z diode in series with the 2 on the board, so the tube gets ~500V as required.
It's ticking happily at:
OK, so I guess the only stuff that is missing is:
sensor.community will not be a problem, we just have to tell Rajko to take in the LND712
From another GM kit (offline only, without WiFi, without LoRa) I have a LND712 (alpha, beta, gamma) which could be put online using multigeiger maybe?
Tube specs: https://www.lndinc.com/products/geiger-mueller-tubes/712/
LND712: 500V (recommended. 450V-650V overall), 10M Anode resistor.
Si22G: 400V (recommended. 360-440V overall).
So, just change the Z-diodes to a sum of 500V?
What I wondered: is putting Z-diodes in series and adding the voltage a valid method?