1) What the MQ-4 senses (and what it does not)

The MQ-4 is specifically designed for detecting methane (CH4), which is the primary combustible gas in natural gas systems.

MQ-4 is sensitive to

• Methane (natural gas)
• Compressed natural gas (CNG)
• Biogas (methane-rich)

MQ-4 is NOT suitable for

• Carbon monoxide (CO)
• Precise ppm measurement without calibration gases
• Selective gas identification in mixed environments

2) How the MQ-4 gas sensor works

The MQ-4 uses a heated tin dioxide (SnO2) sensing layer. Methane molecules reduce the surface resistance of this layer when present.

• Clean air ? high sensor resistance
• Methane present ? resistance decreases
• Resistance change ? voltage change across load resistor

3) Methane selectivity and cross-sensitivity

The MQ-4 is tuned to be more sensitive to methane than many other gases, but it is still cross-sensitive.

• Strong response to methane
• Moderate response to hydrogen
• Lower response to LPG and propane compared to MQ-2

4) Module overview and onboard electronics

The MQ-4 module typically includes:

• MQ-4 sensing element with integrated heater
• Load resistor for voltage divider output
• LM393 comparator for digital alarm output
• Threshold adjustment potentiometer
• Status LED

This makes the module suitable for both qualitative measurement and simple alarm systems.

5) Pinout and electrical characteristics

• Heater current typically 150–200 mA
• Stable 5V supply strongly recommended

6) Heater power and warm-up requirements

The internal heater must reach operating temperature before readings stabilize.

• Initial burn-in (new sensor): several hours recommended
• Typical warm-up before use: 30–60 seconds
• Readings during warm-up are unreliable

7) Analog vs digital outputs

Analog Output (AO)

• Continuous voltage related to methane concentration
• Used for monitoring trends and calibration
• Required for meaningful analysis

Digital Output (DO)

• Comparator-based ON/OFF alarm signal
• Threshold set via onboard potentiometer
• Often active LOW when gas is detected

8) Wiring to Arduino

MQ-4 VCC ? Arduino 5V
MQ-4 GND ? Arduino GND
MQ-4 AO  ? Arduino A0
MQ-4 DO  ? Arduino D2
    

9) Arduino Example 1: Methane level reading

/*
  MQ-4 Methane Sensor - Analog Read
  Product #2711
*/

const int MQ4_AO = A0;

void setup() {
  Serial.begin(9600);
}

void loop() {
  int gasValue = analogRead(MQ4_AO); // 0–1023
  Serial.print("Methane level: ");
  Serial.println(gasValue);
  delay(500);
}
    

10) Arduino Example 2: Natural gas alarm

/*
  MQ-4 Methane Sensor - Digital Alarm
*/

const int MQ4_DO = 2;

void setup() {
  pinMode(MQ4_DO, INPUT);
  Serial.begin(9600);
}

void loop() {
  if (digitalRead(MQ4_DO) == LOW) {
    Serial.println("WARNING: Methane detected!");
  } else {
    Serial.println("Air is normal");
  }
  delay(300);
}
    

11) Arduino Example 3: Software threshold alarm

/*
  MQ-4 Methane Sensor - Software Threshold Alarm
*/

const int MQ4_AO = A0;
const int BUZZER = 8;
const int METHANE_THRESHOLD = 380; // adjust after calibration

void setup() {
  pinMode(BUZZER, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  int value = analogRead(MQ4_AO);

  if (value > METHANE_THRESHOLD) {
    digitalWrite(BUZZER, HIGH);
    Serial.println("ALARM: Methane concentration high");
  } else {
    digitalWrite(BUZZER, LOW);
  }

  delay(200);
}
    

12) Calibration and baseline setup

Calibration is relative and environment-specific.

1. Warm sensor fully
2. Record baseline reading in clean air
3. Introduce controlled methane source if available
4. Set alarm thresholds above baseline

13) Environmental effects and limitations

• Humidity affects sensitivity
• Temperature drift alters readings
• Cross-sensitivity to other hydrocarbons
• Sensor aging over time

14) Typical applications

• Natural gas leak detection experiments
• Biogas monitoring
• Educational gas sensor projects
• Home automation gas alerts (non-certified)

15) Troubleshooting

Always high readings

• Sensor not fully warmed up
• Residual gas in environment
• High humidity or contamination

No response to methane

• Heater not powered correctly
• Incorrect wiring
• Sensor degraded or damaged

16) Quick checklist

MQ-4 Methane Gas Sensor (#2711) Checklist
----------------------------------------
? Use stable 5V supply with enough current
? Allow warm-up before reading values
? Treat readings as relative indicators
? Expect cross-sensitivity to other gases
? Use AO for trends, DO for simple alarms
? Do not use as certified safety device
? Recalibrate periodically