Use an Arduino to Control a Relay

Learn to turn high power devices on and off

Written By: Madeleine Schappi

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A relay is a device that is activated by a current in one circuit to open or close another circuit. 

In this guide, we will learn to use a relay to turn an LED on and off. In this guide, a Little Bird Uno R3 board, the 5V 1-Channel relay board module is used. Please see parts list for a complete list of components required.

After learning to use the 5V 1-Channel relay component, you can use it to turn off lamps, fans, and other appliances up to 250 VAC.

Step 1   Connect Relay to ground

  • Connect an Arduino Ground Pin to the Ground Pin of your relay.

Step 2   Connect Relay to 5V

  • Connect the Arduino 5V pin to the Relay's middle pin.

Step 3   Connect Pin 13 to the Relay

  • Connect Pin 13 to the Relay's Signal pin.

Step 4   Insert LED into Breadboard

  • Insert the LED into the bread board so that the Cathode (shorter pin) is on the left hand side.

Step 5   Insert 200 Ohm Resistor into the breadboard

  • Insert a 220 Ohm Relay so that one pin is in line with the LED's Anode (longer leg)
  • The 220 Ohm Relay has the bands: Red, Red, Black, Black, Brown.

Step 6   Connect LED to Ground

  • Connect the Cathode to a Ground pin on the Arduino.
  • The Cathode is the negative (shorter) leg of the LED.

Step 7   Connect the 3.3V Arduino Pin to the Relay

  • Connect the 3.3V Arduino Pin to the Relay.
  • The 3.3V jumper should go to the NC side of the screw socket.

Step 8   Connect the Relay to the Resistor

  • Connect COM on the relay to the other side of the resistor.

Step 9   Upload the code for your Relay

int relay = 13; // Plug the relay into Digital Pin 13

void setup() {
  pinMode(relay, OUTPUT);

void loop() {
  digitalWrite(relay, HIGH); // Turn the relay on
  delay(1000); // Wait 1 second
  digitalWrite(relay, LOW); // Turn the relay Off
  delay(1000); // Wait 1 second
  • Grab the code and upload it to your board.
  • You should start to hear the click, click of the relay switching on and off. There is also a red light on the module to tell you when it switches.
  • The Relay can be use to control up to 250VAC but we DO NOT recommend you play with this sort of voltage / current unless you are an electrician!

Step 10   In action!

  • This is what a working relay looks (and sounds) like!
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