Arduino - 2-Channel Relay Module

If we need to control two high-voltage devices like pumps, fans, or actuators, we have two options. One option is to use multiple relay modules, but there's an easier way. We can use a 2-channel relay module, which is a single board with two relays built into it. This simplifies the setup and makes it more convenient to control both devices.

Before learning how to use Arduino to control the 2-channel relay module, let's compare a 2-channel relay module to two separate 1-channel relay modules:

Hardware Required

1×Arduino UNO or Genuino UNO
1×USB 2.0 cable type A/B
1×2-channel Relay Module
1×Jumper Wires
1×(Optional) 9V Power Adapter for Arduino
1×(Recommended) Screw Terminal Block Shield for Arduino Uno
1×(Optional) Transparent Acrylic Enclosure For Arduino Uno

Or you can buy the following sensor kit:

1×DIYables Sensor Kit 30 types, 69 units
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About 2-Channel Relay Module

Pinout

2-Channel Relay Module Pinout

A 2-channel relay module has the following pins:

  • Power pins for relay boards
    • DC+: connect this pin to 5V pin of power supply
    • DC-: connect this pin to the GND pin of the power supply and also to the GND pin of the Arduino
  • Signal pins:
    • IN1: this pin receives the control signal from Arduino to control relay 1 on the module
    • IN2: this pin receives the control signal from Arduino to control relay 2 on the module
  • Output pins: NCx (normally closed pin), NOx (normally open pin), COMx (common pin),
    • NC1, NO1, COM1: These pins connect to a high-voltage device that is controlled by relay 1
    • NC2, NO2, COM2: These pins connect to a high-voltage device that is controlled by relay 2

    It also has 2 jumpers to select between the low level trigger and the high level trigger for each relay individually.

    If you want to learn the basic of relay, you can check out the Arduino - Relay tutorial. It provides detailed information on:

    • How to connect relay to high-voltage devices.
    • The terms normally closed and normally open
    • The terms low level trigger and high level trigger
    • How to control relay using Arduino

Wiring Diagram

Arduino 2-channel relay module wiring diagram

This image is created using Fritzing. Click to enlarge image

If you intend to power other components using the 5V pins, it is possible that the relay module may not receive sufficient power. Consequently, it is necessary to utilize an external 5V power source specifically for the module.

So, we need to use three types of power sources:

  • A 5V power adapter for Arduino
  • A 5V power adapter for the 2-channel relay module
  • One or several higher-voltage power adapters (12VDC, 24VDC, 48VDC, 220AC...) for things that are controlled by the 2-channel relay module

The below is the wiring diagram with three power sources. Power supply for Arduino (not included in the image) can be via either USB cable or power jack.

Arduino 2-channel relay module external power source wiring diagram

This image is created using Fritzing. Click to enlarge image

We can cut down on the number of power adapters by using just one 5V power supply for both the Arduino and the 2-channel relay module.

Arduino 2-channel relay module wiring diagram two power source

This image is created using Fritzing. Click to enlarge image

※ NOTE THAT:

If 2 devices that are controlled by a 2-channel relay module use the same voltage, we can use a single high-voltage power adapter for all. However, if they use different voltages, we can use different high-voltage power adapters independently.

How To Program For 2-Channel Relay Module

  • Initializes the Arduino pin to the digital output mode by using pinMode() function.
pinMode(PIN_RELAY_1, OUTPUT); pinMode(PIN_RELAY_2, OUTPUT);
digitalWrite(PIN_RELAY_1, HIGH); digitalWrite(PIN_RELAY_2, HIGH);

Arduino Code

/* * Created by ArduinoGetStarted.com * * This example code is in the public domain * * Tutorial page: https://arduinogetstarted.com/tutorials/arduino-2-channel-relay-module */ #define PIN_RELAY_1 2 // the Arduino pin, which connects to the IN1 pin of relay module #define PIN_RELAY_2 3 // the Arduino pin, which connects to the IN2 pin of relay module // the setup function runs once when you press reset or power the board void setup() { Serial.begin(9600); // initialize digital pin as an output. pinMode(PIN_RELAY_1, OUTPUT); pinMode(PIN_RELAY_2, OUTPUT); } // the loop function runs over and over again forever void loop() { Serial.println("Turn on both relays"); digitalWrite(PIN_RELAY_1, HIGH); digitalWrite(PIN_RELAY_2, HIGH); delay(2000); Serial.println("Turn off both relays"); digitalWrite(PIN_RELAY_1, LOW); digitalWrite(PIN_RELAY_2, LOW); delay(2000); }

Quick Steps

  • Copy the above code and open with Arduino IDE
  • Click Upload button on Arduino IDE to upload code to Arduino
  • Listen the click sound on relays.
  • See the result on Serial Monitor.
COM6
Send
Turn on both relays Turn off both relays Turn on both relays Turn off both relays Turn on both relays Turn off both relays Turn on both relays Turn off both relays
Autoscroll Show timestamp
Clear output
9600 baud  
Newline  

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Function References

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