I have an NPN LJ12A3-4-Z/BX proximity sensor that I want to use to detect water usage on a water meter that has a rotating iron disk.

To make sure I don't overpower the 3.3v GPIO inputs I want to use a reed relay SIP-1A05 to keep the 5v circuit separate. But connecting input pin 18 to the relay does not seem to work.

Do I also need to connect the ground? If so, where to? With a resistor to the relay also?

Thanks water meter circuit

1 Answer 1


Answering my own question so other people can learn from this (after help from Electrical Engineering SE). I should have connected brown and black to the reed relay, not black and blue. Also add pull down resistor to the ground.

corrected circuit

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