Controlling a relay “module” with an Arduino. Here’s a quick demo:
A quick test of a pretty common relay board, the Keyes 5V Relay Module for Arduino.
The relay board includes a transistor switching circuit (to minimise the current drain on the control signal) and diode shunt protection.
So using it is as simple as connecting 5V power and a control signal on one side, and then the relay-switch circuits on the other. The relay offers both normally opan and normally closed circuits. Either or both can be used.
In this case, I have a motor attached to the NO circuit, and an indicator LED on the NC circuit.