Relay Board, Getting Started

A relay is a simple electromagnetic switch. Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits)

Basic Relay Operation

The relay is just a switch, that can be controlled by an electrical signal. The relay does not provide any power, it can open or close an electrical circuit, just like any other switch.

The relay has three terminals Normally Open (NO), Common (COM) and Normally Closed (NC). When the relay is energized the NO terminal is connected to COM. When the relay is de-energized the NC terminal is connected to COM.
Figure 1. Relay Operation

Typical Relay Connection

The following connection diagram shows one way of connecting a light bulb to the relay board. The bulb will turn on when the relay is energized. The 230V AC phase is connected to NO. The 230V AC neutral is connect to one terminal of the bulb. The other terminal is connected to COM. When the relay is energized by making the digital input signal high, the NO is connected to the COM and the bulb will glow.
Figure 2. Typical Relay Connection Diagram

Concluding Notes

Hope this article has helped to get idea about the relay. In the next article, in this series, we will provide sample code, showing how to control a relay from ZDev, ZIO and NuttX.