Monday, October 13, 2014

Single/Multi Channel Relay Board

Good Morning. You may have heard or even used something like a Relay Board and often these boards can cost good amount of money but they are very simple to make so here is a few diagrams for making one. Board diagrams shown here can be used with Arduino or any similar development board.
Typical Relay Board

You can make many different types of Relay boards for ease of explanation I will be separating them based on how many channels they have and the power source they use.

For channels, it is quite simple, each relay will act as a switch so more switch you need more relays to be added and we can simply call each switch a Channel.

These relays can be powered both by the Development board itself or from an external power. If you don't have many external components on your development board and just want to run a single relay, you are fine with using power from the board but if you plan on using good amount of Relays or if they run on 12V you are better off powering the relays from an external 12V source.


These boards are essential if you want to control any external device running on different voltage or maybe controlling something that is on the main line. Say for example you want to make a Remote controlled ceiling light, for that you can easily use a single channel relay board with your development board of choice.

1. Circuit/Vero Board.
2. Diode,
3. Transistor,
4. Relay,
5. Resistor,
6. Connector


7. LED as status indicator. 



Single Channel 5V Relay Board

Single Channel 12V Relay Board

Dual Channel Relay Board
How It works:

Electromagnetic relays are switches that opens or closes with the help of an electromagnet, relays that are used here(the garden variety 5 pin one) usually connects the Common(C) pin to Normally Connected(NC) pin. When the electromagnet is energized with proper voltage the Common(C) pin then disconnects from Normally Connected(NC) and gets connected with Normally Open(NO) pin.
I have written about Relays in much more details so not gonna repeat much, link of that post should be in the Information section below.

Transistors are there to drive those relays as often Signal pins of development boards do not provide enough power.

A LED can be used as an Indicator.


1. While using an external 12V power source for relay, make sure it is regulated unless Relays might make noise/hum.
2. If your Signal pin needs to be pulled down, add that pull down resistor.
3. You can simply add more channels to any of the diagrams and have more relay channels.
4. To use an external source make sure to tie down both ground pins together.

1. Learn about relay here.

2. Read my other posts here.

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