5 Volt 4 Channel Arduino Relay Module User Manual

The Basics

Four Channel Relay ModuleThis relay module allows you to combine the processing power of the Arduino to devices that use higher current and voltage.   It does so by providing four relays that are rated for 7A at either 28VDC or 10A at 125VAC.

Each relay has  a Normally Open (NO) and a Normally Closed (NC) contact.

With these relays you can control:


  • Appliances
  • Motors
  • Lights
  • Other Relay

Where to Purchase the Relay Module

The devices is available nearly everywhere, include the merchants below:



Bang Good


Relay Module Inputs

The module is supplied with power via the pin labeled VCC and ground via the pin labeled GND.

The relays are energized with low inputs to the IN1, IN2, IN3 and IN4 inputs

Four Channel Relay Inputs

Relay Module Outputs.

There are four relays that each provide dry contact outputs.  That is to say that each relay provides a common (COM) , normally open (NO) and a normally closed (NC) terminal.

Four Channel Relay Outputs

Module Schematic

Fundamentally this is four separate circuits on one board.  Other than sharing VCC and ground, the channels are isolated from one another.   See the schematic below:

5V Arduino Four Channel Relay Schematic

Typical Connection to an Arduino

The drawing below shows the typical connections to an Arduino.   In the example shown,  a low output on D7 will cause the light bulb to turn on.

5V Four Channel Relay Arduino Connections

Sample Sketch

As shown in the sketch below, the pin connected to the Arduino output pin is driven low to energize relay and high to de-energize it.

void setup(){  

void loop(){

Useful Information and Links

Songle SRD Relay Data Sheet

Understanding the specs of the Songle SRD-05VDC-SL-C relay will be fundamental to your design.  The datasheet is provided below:

Songle SRD Relay Datasheet

817C Optocoupler Datasheet

The optocoupler is another key component in the circuit.  Understanding its specifications may also be useful.

817C Optocoupler Datasheet

Video Tutorial

The video tutorial below walks you through a basic project.



  1. Curtis December 3, 2016
  2. capnfatz@gmail.com July 11, 2016
  3. George July 9, 2016
  4. capnfatz@gmail.com May 13, 2016
  5. Marek May 7, 2016

Leave a Reply

Your email address will not be published. Required fields are marked *