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.

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

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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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