How to Use MQ 135: Examples, Pinouts, and Specs

The MQ-135 is a versatile gas sensor designed to detect a wide range of gases, including ammonia, nitrogen, oxygen, alcohols, aromatic compounds, sulfide, and smoke. It is widely used in air quality monitoring systems, industrial applications, and safety systems to ensure a healthy and safe environment. The sensor provides an analog output that can be easily interfaced with microcontrollers like the Arduino UNO for real-time monitoring and data logging.

1. Power Supply: Connect the VCC pin to a 5V DC power supply and the GND pin to the ground.
2. Analog Output: Connect the AOUT pin to an analog input pin on your microcontroller (e.g., A0 on Arduino UNO).
3. Digital Output: Optionally, connect the DOUT pin to a digital input pin on your microcontroller if you want to use the threshold-based digital output.

• Preheat Time: The sensor requires a preheat time of at least 24 hours for optimal performance. Ensure the sensor is powered on for this duration before taking any measurements.
• Calibration: Calibrate the sensor in a clean air environment to establish a baseline reading. This helps in accurately detecting gas concentrations.
• Ventilation: Ensure proper ventilation around the sensor to avoid saturation and ensure accurate readings.
• Avoid Contaminants: Keep the sensor away from water, oil, and other contaminants that could affect its performance.

// MQ-135 Gas Sensor - Arduino UNO Example Code

const int analogPin = A0; // Analog input pin connected to AOUT
const int digitalPin = 2; // Digital input pin connected to DOUT (optional)
int sensorValue = 0;      // Variable to store the analog value

void setup() {
  Serial.begin(9600);     // Initialize serial communication at 9600 bps
  pinMode(digitalPin, INPUT); // Set digital pin as input (optional)
}

void loop() {
  sensorValue = analogRead(analogPin); // Read the analog value from the sensor
  Serial.print("Analog Value: ");
  Serial.println(sensorValue); // Print the analog value to the serial monitor

  // Optional: Read the digital output
  int digitalValue = digitalRead(digitalPin);
  Serial.print("Digital Value: ");
  Serial.println(digitalValue); // Print the digital value to the serial monitor

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

1. No Output or Incorrect Readings:

   • Solution: Ensure the sensor is properly connected to the power supply and ground. Check for loose connections and ensure the preheat time is met.

2. Fluctuating Readings:

   • Solution: Ensure the sensor is in a stable environment with consistent airflow. Avoid placing the sensor near sources of interference or contaminants.

3. Slow Response Time:

   • Solution: Verify that the sensor is not saturated with high concentrations of gas. Allow the sensor to recover in clean air if necessary.

1. How long does the sensor last?

   • The MQ-135 sensor has a lifespan of approximately 2 years under normal operating conditions.

2. Can the sensor detect multiple gases simultaneously?

   • Yes, the sensor can detect a range of gases, but it provides a combined output. Specific gas concentration detection requires calibration and additional processing.

3. Is the sensor waterproof?

   • No, the MQ-135 sensor is not waterproof. Avoid exposure to water and other liquids.

By following this documentation, users can effectively integrate the MQ-135 gas sensor into their projects, ensuring accurate and reliable gas detection for various applications.