Smoke Detection using MQ-2 Gas Sensor

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Today in this tutorial we are going to make a “Smoke Detection Circuit” using MQ-2 Gas Sensor & Atmega328p IC. In this example, you will read the MQ-2 sensor analog output voltage and when the smoke reaches a certain level, it will make the sound of a buzzer, and a red LED will turn on. When the output voltage is below that level, a green LED will be on. So let’s get Started!

This Project is sponsored by PCBWay. They have an open-source community, people can share their design projects with each other. Moreover, every time people place an order for your board, PCBWay will donate 10% of the cost of PCB to you, for your contribution to the Open Source Community.

Hardware Required

Sr No	Components	Value	Qty
1	Smoke Sensor	MQ2	1
2	Buzzer	–	1
3	LED	5mm	1
4	Resistor	–	1
5	Bread Board	–	1
7	Jumper wire	–	1

Atmega328p Pinout

MQ2 Pinout

Circuit Diagram

Working Explanation

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 gas.

The smoke sensor has a built-in potentiometer that allows you to adjust the sensor sensitivity according to how accurately you want to detect gas.

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

Atmega328p Code

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);
}