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What is a Relay?

A Relay is an electrically operated switch.Relays control one electrical circuit by opening and closing contacts in another circuit.Many relays use an electromagnet to mechanically operate a switch, but other operating principles are also used, such as solid-state relays.Relays are used where it is necessary to control a circuit by a separate low-power signal where the output is a high voltage, or where several circuits must be controlled by one signal.In our IoT home automation projects using Raspberry Pi it can control ow voltage devices of 3.3 V, however when we speak about 220 V of AC Raspberry Pi cannot handle it. So we uses a Relay switch which have Normally Open (NO) and Normally Closed (NC) Pins which is controlled by low voltage. Refer the below diagram to understand Raspberry Pi Relay Control.

  1. Normally Open (NO) : The circuit is disconnected when the relay is inactive.

  2. Normally Closed (NC) : The circuit is connected when the relay is inactive.

The relay switch is utilized by means of a low-voltage to control the AC connected in NO or NC pins. Since the Pi only tolerates a maximum of 5V and the GPIOs only 3.3V without relays the Pi could burn out if you use direct connections to GPIO pins. We will not controlling ac with raspberry pi in this relay raspberry pi tutorial tutorial however we will be controlling led with relay and raspberry pi.

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