User Manual

Working of Relay

The working principle of relay is simple. When power is supplied to the relay, currents start

flowing through the control coil; as a result, the electromagnet starts energizing. Then the

armature is attracted to the coil, pulling down the moving contact together thus connecting

with the normally open contacts. So the circuit with the load is energized. Then breaking the

circuit would a similar case, as the moving contact will be pulled up to the normally closed

contacts under the force of the spring. In this way, the switching on and off of the relay can

control the state of a load circuit.

Connect the base electrode of the transistor to GPIO0. When we make GPIO0 output high

level (3.3V) by programming, the transistor will conduct because of current saturation. The

normally open contact of the relay will be closed, while the normally closed contact of the

relay will be broken; when we make it output low level (0V), the transistor will be cut off, and

the relay will recover to initial state.