How to Use MQ 4: Examples, Pinouts, and Specs

The MQ-4 is a gas sensor designed to detect methane (CH₄) and natural gas concentrations in the air. It operates on the principle of resistive change, where the sensor's resistance varies in the presence of target gases. The MQ-4 provides an analog output signal proportional to the gas concentration, making it suitable for a wide range of applications.

• Gas leak detection in homes and industries
• Methane monitoring in mining and oil fields
• Natural gas detection in HVAC systems
• Environmental monitoring systems
• IoT-based gas detection projects

The MQ-4 sensor is a robust and reliable component with the following key specifications:

The MQ-4 sensor typically comes with four pins or six pins, depending on the module version. Below is the pin configuration for the 4-pin version:

For the 6-pin version, two additional pins are used for the internal heater connections (H1 and H2). These are typically pre-wired in most modules.

1. Power the Sensor: Connect the VCC pin to a 5V DC power supply and the GND pin to ground.
2. Read the Output:
   • Use the AOUT pin to read the analog voltage signal, which varies with the gas concentration.
   • Optionally, use the DOUT pin for a digital signal if the module includes a comparator circuit.
3. Preheat the Sensor: Allow the sensor to preheat for at least 24 hours before initial use to stabilize its readings.
4. Connect to a Microcontroller: The analog output can be connected to an ADC (Analog-to-Digital Converter) pin of a microcontroller like the Arduino UNO for further processing.

• Preheating: The sensor requires a preheating period of 24 hours for accurate readings. For subsequent uses, a shorter warm-up time (a few minutes) is sufficient.
• Calibration: Calibrate the sensor in a known gas concentration environment to improve accuracy.
• Ventilation: Ensure proper ventilation around the sensor to avoid saturation and false readings.
• Load Resistor: Adjust the load resistor (RL) value to optimize the sensor's sensitivity and output range.
• Avoid Contaminants: Keep the sensor away from water, oil, and corrosive gases, as these can damage the sensing element.

Below is an example of how to connect the MQ-4 sensor to an Arduino UNO and read the analog output:

• Connect the MQ-4's VCC pin to the Arduino's 5V pin.
• Connect the GND pin to the Arduino's GND.
• Connect the AOUT pin to the Arduino's analog input pin (e.g., A0).

// MQ-4 Gas Sensor Example with Arduino UNO
// Reads the analog output of the MQ-4 sensor and prints the value to the Serial Monitor

const int gasSensorPin = A0; // Analog pin connected to MQ-4 AOUT
int sensorValue = 0;         // Variable to store the sensor reading

void setup() {
  Serial.begin(9600); // Initialize serial communication at 9600 baud
  Serial.println("MQ-4 Gas Sensor Test");
}

void loop() {
  sensorValue = analogRead(gasSensorPin); // Read the analog value from the sensor
  Serial.print("Gas Sensor Value: ");
  Serial.println(sensorValue); // Print the sensor value to the Serial Monitor

  delay(1000); // Wait for 1 second before the next reading
}

• The analogRead() function reads the voltage from the AOUT pin and converts it to a digital value (0–1023 for a 10-bit ADC).
• The sensor value can be mapped to a gas concentration using a calibration curve provided in the sensor's datasheet.

1. No Output Signal:

   • Check the power supply connections (VCC and GND).
   • Ensure the sensor has completed its preheating period.

2. Inaccurate Readings:

   • Verify the load resistor (RL) value is correctly set.
   • Calibrate the sensor in a known gas concentration environment.

3. Fluctuating Output:

   • Ensure the sensor is in a stable environment with consistent airflow.
   • Avoid placing the sensor near heat sources or strong electromagnetic fields.

4. Sensor Not Responding to Gas:

   • Confirm the target gas is within the sensor's detection range.
   • Check for physical damage to the sensor or contamination.

Q: Can the MQ-4 detect gases other than methane?
A: While the MQ-4 is optimized for methane and natural gas, it may respond to other combustible gases. However, its sensitivity and accuracy for non-target gases may be lower.

Q: How long does the MQ-4 last?
A: The sensor typically has a lifespan of 2–3 years under normal operating conditions.

Q: Can I use the MQ-4 outdoors?
A: The MQ-4 can be used outdoors, but it should be protected from water, extreme temperatures, and high humidity to ensure reliable operation.

Q: Is the digital output (DOUT) always available?
A: The DOUT pin is only available on MQ-4 modules with an onboard comparator circuit. Check your module's specifications to confirm.

By following this documentation, users can effectively integrate the MQ-4 gas sensor into their projects for reliable methane and natural gas detection.