Guide for MQ-2 Gas/Smoke Sensor with Arduino

This guide shows how to build a smoke detector that beeps when it detects flammable gas or smoke.

The MQ-2 Gas Sensor

The MQ-2 smoke sensor is the one in the following figure:

The MQ-2 smoke sensor is sensitive to smoke and to the following flammable gases:

• LPG
• Butane
• Propane
• Methane
• Alcohol
• Hydrogen

The resistance of the sensor is different depending on the type of the gas.

The smoke sensor has a built-in potentiometer that allows you to adjust the sensor digital output (D0) threshold. This threshold sets the value above which the digital pin will output a HIGH signal.

How does it work?

The voltage that the sensor outputs changes accordingly to the smoke/gas level that exists in the atmosphere. The sensor outputs a voltage that is proportional to the concentration of smoke/gas.

In other words, the relationship between voltage and gas concentration is the following:

• The greater the gas concentration, the greater the output voltage
• The lower the gas concentration, the lower the output voltage

The output can be an analog signal (A0) that can be read with an analog input of the Arduino or a digital output (D0) that can be read with a digital input of the Arduino.

Pin Wiring

The MQ-2 sensor has 4 pins.

Example: Gas Sensor with Arduino

In this example, you will read the sensor analog output voltage and when the smoke reaches a certain level, it will make sound a buzzer and a red LED will turn on.

When the output voltage is below  that level, a green LED will be on.

Parts needed:

So, for this example, you’ll need:

• 1 x MQ-2 gas sensor 
• Arduino UNO – read Best Arduino Starter Kits
• 1x Breadboard 
• 1 x red LED
• 1 x green LED
• 1 x buzzer
• 3 x 220Ω resistor
• Jumper wires

You can use the preceding links or go directly to MakerAdvisor.com/tools to find all the parts for your projects at the best price!

Schematics

Follow these schematics to complete the project:

Code

Upload the following sketch to your Arduino board (feel free to adjust the variable sensorThres with a different threshold value):

/*******
 
 All the resources for this project:
 https://randomnerdtutorials.com/

*******/

int redLed = 12;
int greenLed = 11;
int buzzer = 10;
int smokeA0 = A5;
// Your threshold value
int sensorThres = 400;

void setup() {
  pinMode(redLed, OUTPUT);
  pinMode(greenLed, OUTPUT);
  pinMode(buzzer, OUTPUT);
  pinMode(smokeA0, INPUT);
  Serial.begin(9600);
}

void loop() {
  int analogSensor = analogRead(smokeA0);

  Serial.print("Pin A0: ");
  Serial.println(analogSensor);
  // Checks if it has reached the threshold value
  if (analogSensor > sensorThres)
  {
    digitalWrite(redLed, HIGH);
    digitalWrite(greenLed, LOW);
    tone(buzzer, 1000, 200);
  }
  else
  {
    digitalWrite(redLed, LOW);
    digitalWrite(greenLed, HIGH);
    noTone(buzzer);
  }
  delay(100);
}