How to Use mq135: Examples, Pinouts, and Specs

The MQ135 is a versatile gas sensor designed to detect a wide range of gases, including ammonia (NH3), benzene (C6H6), alcohol, smoke, and other harmful gases. It operates on the principle of resistive change, where the sensor's resistance varies in the presence of target gases. This change is converted into an analog output signal, making it suitable for air quality monitoring and environmental sensing applications.

• Air quality monitoring systems
• Industrial gas detection
• Smoke and fire detection systems
• Environmental pollution monitoring
• Home automation for air quality control

The MQ135 sensor is designed for ease of use and integration into various systems. Below are its key technical details:

The MQ135 sensor typically comes with four pins. Below is the pinout description:

The MQ135 sensor is straightforward to use in a circuit. Follow the steps below to integrate it into your project:

1. Connect the VCC pin to a 5V power supply.
2. Connect the GND pin to the ground of your circuit.
3. Connect the AOUT pin to an analog input pin of your microcontroller (e.g., Arduino).
4. Optionally, connect the DOUT pin to a digital input pin if you want to use the digital threshold feature.

• Preheating: The sensor requires a preheating time of at least 24 hours for accurate readings. During this time, the internal heater stabilizes the sensor's performance.
• Calibration: The sensor's output varies with environmental conditions. Calibrate the sensor in a controlled environment to ensure accurate gas concentration readings.
• Power Supply: Use a stable 5V power source to avoid fluctuations in the sensor's output.
• Ventilation: Ensure proper ventilation around the sensor to allow free flow of air for accurate gas detection.

Below is an example of how to use the MQ135 sensor with an Arduino UNO to read analog values:

// MQ135 Gas Sensor Example Code
// This code reads the analog output of the MQ135 sensor and prints the value
// to the Serial Monitor. Ensure the sensor is connected to the correct pins.

const int analogPin = A0; // Connect AOUT pin of MQ135 to A0 on Arduino

void setup() {
  Serial.begin(9600); // Initialize serial communication at 9600 baud
  Serial.println("MQ135 Gas Sensor Test");
  delay(1000); // Allow time for the sensor to stabilize
}

void loop() {
  int sensorValue = analogRead(analogPin); // Read analog value from MQ135
  float voltage = sensorValue * (5.0 / 1023.0); // Convert to voltage (0-5V)
  
  // Print the raw sensor value and voltage to the Serial Monitor
  Serial.print("Sensor Value: ");
  Serial.print(sensorValue);
  Serial.print(" | Voltage: ");
  Serial.print(voltage);
  Serial.println(" V");
  
  delay(1000); // Wait 1 second before the next reading
}

• The analog value read from the sensor can be used to estimate gas concentration after proper calibration.
• The voltage variable represents the sensor's output voltage, which is proportional to the gas concentration.

1. No Output or Incorrect Readings

   • Cause: Insufficient preheating time.
   • Solution: Allow the sensor to preheat for at least 24 hours before taking measurements.

2. Fluctuating Readings

   • Cause: Unstable power supply or environmental interference.
   • Solution: Use a regulated 5V power source and ensure the sensor is placed in a stable environment.

3. Low Sensitivity

   • Cause: Sensor aging or contamination.
   • Solution: Replace the sensor if it has been in use for more than 2 years or exposed to harsh conditions.

4. Digital Output Not Triggering

   • Cause: Incorrect threshold setting.
   • Solution: Adjust the potentiometer on the sensor module to set the desired threshold.

1. Can the MQ135 detect multiple gases simultaneously?

   • Yes, the MQ135 can detect a variety of gases, but it does not differentiate between them. Calibration is required to estimate specific gas concentrations.

2. How do I calibrate the MQ135 sensor?

   • Calibration involves exposing the sensor to a known concentration of the target gas and recording the corresponding output voltage. Use this data to create a mapping function for your application.

3. Is the MQ135 suitable for outdoor use?

   • The MQ135 can be used outdoors, but it should be protected from extreme weather conditions and high humidity to ensure accurate readings.

4. What is the lifespan of the MQ135 sensor?

   • Under normal operating conditions, the sensor has a lifespan of approximately 2 years.

By following this documentation, you can effectively integrate the MQ135 gas sensor into your projects and ensure reliable performance.