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 2.GQ Geiger Muller Counter
 Get a Logic Pulse out of a counter for each Count?		  New Topic  Reply to Topic
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ullix

Germany
1241 Posts
Posted - 01/27/2026 :  09:00:06  Show Profile  Reply with Quote
Particularly from a GMC-800? Preferentially the Logic-Pulse should have 3.3V, active Hi, Pulse Width 100...150 µs.

I am prepared to solder a connection onto the board!
Reply #1

EmfDev

2387 Posts
Posted - 01/27/2026 :  15:52:17  Show Profile  Reply with Quote
middle pin of LED but it is active low and is an open collector when not active.
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Reply #2

ullix

Germany
1241 Posts
Posted - 01/28/2026 :  03:15:24  Show Profile  Reply with Quote
Thx! The only LED I see is a 2-color LED with 4 pins, which makes it difficult to find the middle one ;-)

But on testing the 2 outer pins seem to carry the same signal. This is an active Low of 2.0V and a width of 720#181;s.

Are you sure this is the signal for counting? Because its lenght limits any counter to 1 / 720 #181;s or below CPS=1389, CPM=83333?
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Reply #3

EmfDev

2387 Posts
Posted - 01/29/2026 :  15:30:52  Show Profile  Reply with Quote
I think it comes from resistor R9. It is not directly from the real pulse so the duration is not the same as from the pulse counter.

You can connect your probe to V3-C pin but it may generate false counts to the device.
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Reply #4

ullix

Germany
1241 Posts
Posted - 01/30/2026 :  03:31:40  Show Profile  Reply with Quote
I get nothing at R9, nor at its neighbor R26.

But at V3-C I get a beatiful signal, Active-Lo, ~3.3V, length fluctuating 100...120#181;s!

This works, thank you!
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