PNP/NPN detection circuit

21

Hey Bob.

Apologies for the late replayed I’ve been away on holiday.

Came back with fresh eyes and decided to measure the current through the LEDs and I can confirm there is no current flowing without an input.

You are likely correct that the small current I seen was being used by the comparator and other areas possibly.

Needless to say I’m happy the first design without R9 and R10 work exactly how I want it to.

I have since removed the LEDs and inserted some optocouplers which are connected to an Arduino with OLED

Thanks again for your help.

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22

Hi Larry
All good. If you are not inclined to follow up the R9 and R10 behaviour that is OK. Be aware though tat with very high impedance inputs left floating you might experience the occasional strange happening from time to time.

Fitting R11 and R12 should get rid of any minute LED illumination. If you replace the LRDs with Opto Couplers you might get some intermittent strange switching as some of these couplers are pretty sensitive and operate with very small currents.
Cheers Bob

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