Optocoupler Relay Module

A Relay is a digital switch that controls much higher voltages and currents than your normal Arduino boards. When a logic voltage is applied, the relay will switch to allow current to flow or cut off, depending on your wiring. A Relay usually consists of a coil, 1 common terminal, 1 normally closed terminal, and one normally open terminal. When the coil is energized, the common terminal and the normally open terminal will have continuity.

Why do we want to use a relay and do we really need to? Anytime you want to switch on/off a device that draws more current or works with a high voltage, you’ll need to use a relay, such as controlling headlights, parking lights, horns, etc.