Relay a Electromechanical Switch
In general, It has 5 pins described below:
|1.||Input 1||Apply Signal to trigger relay, either positive or negative signal.|
|2.||Input 2||Apply Signal to trigger relay signal opposite to input 1 (if positive to input 1 then negative here or vice versa).|
|3.||COM (common)||Com point where you connect the one terminal of ground or supply voltage (recommended) you want to give to the load either 5V/12V/24V DC or 110V/220V AC etc.|
|4.||NO (Normally open)||Switching terminal, when relay gets triggered than arm of relay trip to NO terminal. So the signal from com will directed to NO terminal of the relay.|
|5.||NC(Normally close)||When relay don’t get triggered, signal connected to common point will directed to NC terminal of the relay.|
You can apply positive signal to either of the input (input 1/ input 2) but on the other input must be ground (negative) signal. Keep in mind potential difference between the inputs must be the voltage of relays rating.
For example, we have a 5V DC relay, apply +5V to input 1 and ground to input 2 (makes 5V potential difference) or you can give +12 V to input 1 and +7 V to input 2 it will also work because of potential difference of 5V.
When a current flows through the relays coil an electro-magnetic field is set up. This electromagnetic field attracts an iron armature, whose other end pushes the contacts together, completing the circuit.