[Swlug] DIY Geiger counter

[James R. Haigh (+ML.LUG subaddress)]

At Z+0000=2025-03-09Sun21:44:56, Rhys Sage sent:
> The big thick leads in the photo go to the scope/ [...]

    Do you mean the crocodile clips?  But the flat purple jumper wire or far-side node 18 on your breadboard is meant to be a positive supply if you match it with the Instructables amplifier design.  That's why I guessed that the red croc clip was the positive side of a 2nd supply.  But if you're saying that this is actually a scope lead then maybe that is one of your problems -- there'd be no power to your 1st transistor.

    I can't see anything else in the picture that would be considered a "big thick lead", except maybe the yellow/green pair look a bit thicker -- but you already confirmed that this pair is from the photodiode...

> The yellow/green pair go to the photodiode.

    So by process of elimination, the only "big thick leads" in the photo are the crocodile clips, and therefore it looks like your 1st transistor is not powered.

    By nature of an open-collector output, your 2nd transistor is "powered" by whatever its output is that it is sinking current for.  Okay, it makes sense that the black croc clip is a scope input because it is connected to this open-collector output.  It also makes sense that the other scope lead connects to a power rail as its common current return path.

    So I'm wondering whether you missed a jumper between your breadboard near-side outer/positive rail and near-side node 19 that the red croc clip connects to via the pin that probably started life as a paperclip -- or whether you do have a 2nd power supply off-photo whose positive side shares the red crocodile clip.

    It's another thing worth checking, anyway.

Kind regards,
James.
-- 
Wealth doesn't bring happiness, but poverty brings sadness.
Sent from Debian with Claws Mail, using email subaddressing as an alternative to error-prone heuristical spam filtering.
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