5V Relay: Pinout, Description, Working & Datasheet Sep 26, 20173V Relay, 12V Relay, 1-channel Relay module, 4-channel Relay Module. How to use a Relay. Relays are most commonly used switching device in electronics. Let us learn how to use one in our circuits based on the requirement of our project. Before we proceed with the circuit to drive the relay we have to consider two important parameter of the relay. How to use a relay | BuildCircuit There are 5 Pins in a relay. Two pins A and B are two ends of a coil that are kept inside the relay. The coil is wound on a small rod that gets magnetized whenever current passes through it. COM/POLE is always connected to NC(Normally connected) pin.