Arduino - Gas Sensor - Relay

We are going to learn how to use the Arduino, gas sensor and relay do activate the fan or siren when detecting the LPG, smoke, alcohol, propane, hydrogen, methane and carbon monoxide, or other flammable gasses.

Hardware Required

1×Arduino UNO or Genuino UNO
1×USB 2.0 cable type A/B
1×MQ2 Gas Sensor
1×Jumper Wires
1×(Optional) 12V Cooling Fan
1×(Optional) 12V Alarm Siren Horn
1×(Optional) 12V Power Adapter
1×(Optional) DC Power Jack
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
Please note: These are Amazon affiliate links. If you buy the components through these links, We will get a commission at no extra cost to you. We appreciate it.

About Relay and MQ2 Gas Sensor

If you do not know about relay and MQ2 Gas Sensor (pinout, how it works, how to program ...), learn about them in the following tutorials:

Wiring Diagram

Arduino MQ2 Gas Sensor Relay Wiring Diagram

This image is created using Fritzing. Click to enlarge image

Arduino Code

/* * Created by * * This example code is in the public domain * * Tutorial page: */ #define DO_PIN 12 // Arduino's pin connected to DO pin of the MQ2 sensor #define RELAY_PIN 2 // Arduino's pin connected to relay void setup() { // initialize serial communication Serial.begin(9600); // initialize the Arduino's pin as an input pinMode(DO_PIN, INPUT); pinMode(RELAY_PIN, OUTPUT); Serial.println("Warming up the MQ2 sensor"); delay(20000); // wait for the MQ2 to warm up } void loop() { int gasState = digitalRead(DO_PIN); if (gasState == HIGH) { Serial.println("The gas is NOT present"); digitalWrite(RELAY_PIN, LOW); // turn off } else { Serial.println("The gas is present"); digitalWrite(RELAY_PIN, HIGH); // turn on } }

Quick Steps

  • Connect Arduino to PC via USB cable
  • Open Arduino IDE, select the right board and port
  • Copy the above code and open with Arduino IDE
  • Click Upload button on Arduino IDE to upload code to Arduino
Arduino IDE Upload Code
  • Move your hand in front of sensor
  • See the change of relay's state

Code Explanation

Read the line-by-line explanation in comment lines of source code!

Video Tutorial

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The Best Arduino Starter Kit