What is a relay and how can it be used to control electrical devices?
A relay is a switch. You can turn on the switch by applying a small electric current to the coil inside the relay. A relay has four terminals (aka contacts or “pins”) – two that are connected to the coil – connect these two to a battery, and the relay will turn on. The other two pins are the pins of the switch, you connect your circuit to them and if the relay switches on current can flow through one pin and out the other. They’re used to control very large currents (for example turning on the indiciator /signal lights in your car), using only a small current signal (for example the signal from your car’s computer that turns the indicator lights on and off once per second). The computer alone can’t handle the current needed to power the lights, so the computer powers on the relay’s coil (which only needs a small amount of current), and then the relay is used to turn the lights on or off. The relay is obviously just a switch – the power for turning on the lights comes from the battery o
