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?