Connecting a Relay to an Arduino

These instructions will go through the basics of a relay and what its terminals mean. Though this one has been used to switch on and off a 12v light, there are many many other potential applications as well!

5v to 12v (or whatever output voltage you'll need) relay

arduino

power supply

To wedge the end of a wire into the terminal, first loosen the top screw before inserting the stripped wire end (or any M end on the jumper wire). Then tighten screw to hold the wire in place.

These are the relay terminal to other terminal connections you'll need to make in order to complete the circuit:

DC+ : connect to 5v terminal on Arduino via jumper wire

DC- : connect to ground terminal on Arduino via jumper wire

IN - : connect to any of the digital output terminals on Arduino via jumper wire

NO (normally open) : connect to positive terminal on power supply (use NO or NC separately, not at the same time); the circuit will be open (off) unless switched on

COM : connect to positive lead on object

NC (normally closed) : connect to positive terminal on power supply (use NO or NC separately, not at the same time); the circuit will be closed (on) unless switched off

The negative lead on the object should be connected to the -v terminal on the power supply to complete the circuit.

In the case where you need to use more than one relay and there aren't enough open 5v or ground terminals on the Arduino, you'll have to wire the 5v and ground terminals to the + and - rails (respectively) on a breadboard.