MQ-2 Gas & Smoke Sensor Tutorial

1. Introduction

The MQ-2 is a versatile gas sensor that can detect combustible gases and smoke. It's commonly used in DIY smoke detectors, gas leak alarms, and air quality monitors.

📦 Gases Detected

LPG (Liquefied Petroleum Gas)
Methane (Natural Gas)
Propane
Butane
Hydrogen
Smoke

⚠️ Safety Warning

This sensor is for educational purposes only. Do NOT use it as the sole safety device for life-critical applications. Always use certified commercial gas detectors for safety-critical installations.

2. Technical Specifications

Parameter	Specification
Operating Voltage	5V DC
Heater Current	~150mA
Detection Range	300-10000 ppm
Preheat Time	20+ seconds (24-48hrs for accurate calibration)
Output Type	Analog (AO) + Digital (DO)
Digital Trigger	Adjustable via potentiometer

How It Works

The MQ-2 uses a tin dioxide (SnO2) semiconductor that changes resistance when exposed to gases:

Internal heater warms the sensing element
Clean air: High resistance → Low output voltage
Gas present: Low resistance → High output voltage
Compare voltage to threshold for detection

⚠️ Preheat Required

The sensor needs to warm up for at least 20 seconds before readings are stable. For accurate calibration, run continuously for 24-48 hours in clean air.

3. Wiring Guide

MQ-2 Pin	Description	Arduino	ESP32
VCC	Power (5V)	5V	VIN/5V
GND	Ground	GND	GND
AO	Analog Output	A0	GPIO 34
DO	Digital Output	Pin 2	GPIO 13

Figure 1: MQ-2 sensor wiring with Arduino

💡 Module Features

Potentiometer: Adjusts the digital output (DO) threshold

LEDs: Power indicator + alarm indicator

4. Project: Smoke & Gas Alarm

Basic Gas Detection

const int analogPin = A0;
const int digitalPin = 2;
const int buzzerPin = 8;

void setup() {
    Serial.begin(115200);
    pinMode(digitalPin, INPUT);
    pinMode(buzzerPin, OUTPUT);
    
    Serial.println("MQ-2 Gas Sensor");
    Serial.println("Warming up (20 seconds)...");
    delay(20000);  // Preheat time
    Serial.println("Ready!");
}

void loop() {
    int gasLevel = analogRead(analogPin);
    int alarm = digitalRead(digitalPin);

    Serial.print("Gas Level: ");
    Serial.print(gasLevel);

    if (alarm == LOW) {  // LOW = threshold exceeded
        Serial.println(" | ALARM: GAS DETECTED!");
        digitalWrite(buzzerPin, HIGH);
    } else {
        Serial.println(" | Status: Normal");
        digitalWrite(buzzerPin, LOW);
    }

    delay(500);
}

Gas Level Monitor with Categories

const int analogPin = A0;

void setup() {
    Serial.begin(115200);
    Serial.println("MQ-2 Warming up...");
    delay(20000);
    Serial.println("Ready!");
}

void loop() {
    int gasLevel = analogRead(analogPin);
    
    Serial.print("Gas Level: ");
    Serial.print(gasLevel);
    Serial.print(" | Status: ");
    
    if (gasLevel < 200) {
        Serial.println("Clean Air");
    } else if (gasLevel < 400) {
        Serial.println("Low Gas Detected");
    } else if (gasLevel < 600) {
        Serial.println("Moderate - Check Area!");
    } else {
        Serial.println("HIGH - DANGER!");
    }
    
    delay(1000);
}

5. Calibration Tips

Run the sensor in clean air for 24-48 hours
Note the baseline reading (typically 100-200)
Set your alarm threshold above baseline + margin
Test with a lighter (briefly release butane near sensor)
Adjust potentiometer to set DO trigger point

6. Applications

Smoke detection: DIY fire alarm systems
Gas leak detection: Kitchen safety monitors
Industrial safety: Workshop ventilation triggers
Robotics: Hazardous environment detection

7. Troubleshooting

Always reads high value

Allow longer preheat time
Ensure good ventilation around sensor

Not detecting gas

Check 5V power supply (not 3.3V)
Verify sensor is heated (check for warmth)

8. Summary

Detects LPG, methane, propane, butane, hydrogen, smoke
Requires 5V and 20+ second preheat
Analog output (AO) for gas concentration level
Digital output (DO) for threshold alarm
Potentiometer adjusts DO trigger threshold