Introduction

The MQ-2 is a semiconductor gas sensor that detects combustible gases including LPG, propane, methane, hydrogen, alcohol, and smoke. With its high sensitivity and fast response time, it's widely used in gas leak detectors, fire alarms, and air quality monitors.

Key Features

Technical Specifications

Pin Configuration

Pin	Label	Description	Arduino Connection
1	VCC	Power (5V ±0.1V)	5V
2	GND	Ground	GND
3	DO	Digital Output	D2 (Digital Input)
4	AO	Analog Output	A0 (Analog Input)

Wiring Diagram (Arduino)

// Basic Connections:
// VCC → 5V (must be 5V ±0.1V)
// GND → GND
// AO  → A0 (Analog Input)
// DO  → D2 (Digital Input - optional)

// For best results:
// - Allow 24-48 hours for initial stabilization
// - Keep sensor away from direct airflow

Basic Gas Detection

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

void setup() {
  Serial.begin(9600);
  pinMode(digitalPin, INPUT);
}

void loop() {
  int analogValue = analogRead(analogPin);
  int digitalValue = digitalRead(digitalPin);
  
  Serial.print("Gas Level: ");
  Serial.print(analogValue);
  Serial.print(" | Alarm: ");
  Serial.println(digitalValue);
  
  if(digitalValue == LOW) {
    Serial.println("Gas detected!");
  }
  
  delay(1000);
}

Advanced Applications

// Calibrate in clean air
float R0 = 0;
const int cleanAirFactor = 9.83; // Sensor specific

void setup() {
  // After 24h warmup in clean air
  float sensor_volt = analogRead(A0)*(5.0/1023.0);
  float RS_air = (5.0-sensor_volt)/sensor_volt;
  R0 = RS_air/cleanAirFactor;
  Serial.print("R0 = "); Serial.println(R0);
}

// Convert to PPM (LPG example)
float getPPM_LPG(float R0) {
  float sensor_volt = analogRead(A0)*(5.0/1023.0);
  float RS_gas = (5.0-sensor_volt)/sensor_volt;
  float ratio = RS_gas/R0;
  
  // Empirical values for LPG
  float ppm = 1000 * pow(10, (log10(ratio)-0.8)/(-0.4));
  return ppm;
}

// Add temperature compensation
#include "DHT.h"
DHT dht(DHTPIN, DHT11);

void loop() {
  float temp = dht.readTemperature();
  float analogValue = analogRead(A0);
  
  // Simple compensation (adjust coefficients)
  float compensated = analogValue * (1 + (25 - temp)*0.02);
}

// Send SMS alert when gas detected
#include 

void sendAlert() {
  GSM_SMS sms;
  sms.beginSMS("+1234567890");
  sms.print("GAS LEAK DETECTED!");
  sms.endSMS();
}

void loop() {
  if(digitalRead(D2) == LOW) {
    sendAlert();
    delay(60000); // Prevent SMS flood
  }
}

Troubleshooting