PROJECT 06 – RELAYS

INTRODUCTION

A relay is a device that allows one circuit to control another circuit. It allows one circuit to turn on or off the other circuit – so it's an electrically controlled switch. The general use is to allow a circuit with a small current to control a circuit with a larger current. Below is a relay that resembles one of the models that we have in class:

The controlling circuit is called the primary circuit while the circuit that is controlled is called the secondary circuit.

For us, this is useful because devices such as Arduinos can be damaged by high currents. On the other hand, motors require higher currents than Arduinos can handle. So, by using a relay, we can control motors with Arduinos without really connecting the two.

INSIDE A RELAY

The diagram below shows how the inside of the relay changes when the primary circuit is powered ON versus when it is OFF. As you can see, the switch that closes the secondary circuit changes positions based on the state of the primary circuit.

RELAYS WITH BOTH NO AND NC

Some relays connect the secondary circuit's switch to two different pins so that the switch has one common pin (C) at one end and two pins at the other end: one normally open (NO) and one normally closed (NC).

DEVICES WITH TWO RELAYS ON-BOARD

Some relay devices have two pins for the primary circuit, three pins for the secondary circuit and another three pins for another secondary circuit.

PINOUT

The above graphic shows the pinout diagram of our relays. When the coil between pins 1 and 16 is disconnected, the COM pin is connected to its corresponding NC pin. When the coil pins are powered, the COM pin is now connected to its corresponding NO pin.

WORK

Get a relay from Mr. Campeau. It should have the NO and NC options on it.

Connect the primary circuit pins to a power source.

Connect the NC pin to LED, resistor and a second power source.

Connect the NO pin to a different LED and resistor and then to the same second power source.

Testing: When the primary circuit is OFF, one LED should be on. When the primary circuit is ON, the other LED should be on instead.

Show Mr. Campeau.