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, benzene, alcohol, and smoke. Manufactured by ESP32 with the part ID 001, this sensor operates on the principle of resistive change when exposed to target gases. It provides an analog output that can be easily interfaced with microcontrollers, making it ideal for air quality monitoring and environmental sensing applications.

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

The MQ135 sensor is designed for ease of use and reliable performance. Below are its key technical details:

The MQ135 sensor typically comes with a 4-pin interface. 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 UNO).
4. Optionally, connect the DOUT pin to a digital input pin if you want to use the threshold-based digital output.

• 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: For precise measurements, calibrate the sensor in a clean air environment to establish a baseline reading.
• Power Supply: Ensure a stable 5V power supply to avoid fluctuations in the sensor's output.
• Ventilation: Place the sensor in a well-ventilated area to avoid saturation and ensure 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 MQ135_PIN = A0; // Connect AOUT pin of MQ135 to Arduino analog pin A0

void setup() {
  Serial.begin(9600); // Initialize serial communication at 9600 baud
  Serial.println("MQ135 Gas Sensor Test");
}

void loop() {
  int sensorValue = analogRead(MQ135_PIN); // 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 for 1 second before the next reading
}

• Use a load resistor (RL) of 10 kΩ for typical applications.
• Avoid exposing the sensor to high concentrations of corrosive gases for extended periods, as this may damage the sensor.
• Place the sensor in a vertical orientation to ensure proper airflow.

1. No Output or Incorrect Readings

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

2. Fluctuating Readings

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

3. Sensor Saturation

   • Cause: Prolonged exposure to high concentrations of target gases.
   • Solution: Remove the sensor from the high-concentration environment and allow it to recover in clean air.

4. Digital Output Not Triggering

   • Cause: Threshold not properly set on the onboard potentiometer.
   • Solution: Adjust the potentiometer to set the desired gas concentration threshold.

Q1: Can the MQ135 detect multiple gases simultaneously?
A1: Yes, the MQ135 can detect a variety of gases, but it does not differentiate between them. It provides a combined analog output based on the total concentration of detected gases.

Q2: How do I calibrate the MQ135 sensor?
A2: To calibrate, expose the sensor to clean air and record the baseline analog output. Use this value to calculate gas concentrations in your application.

Q3: Can I use the MQ135 with a 3.3V microcontroller?
A3: The MQ135 requires a 5V power supply for proper operation. However, you can use a voltage divider or level shifter to interface its output with a 3.3V microcontroller.

Q4: What is the lifespan of the MQ135 sensor?
A4: The MQ135 has a typical lifespan of 2-3 years under normal operating conditions. Regular maintenance and proper usage can extend its life.

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