MQ 135 Air Quality/Gas Detector Sensor Module

The MQ-135 is a widely used air quality sensor designed to detect a range of gases and air pollutants. It is part of the MQ series of sensors from MQ Gas Sensors, and is commonly used in projects related to air quality monitoring, pollution detection and environmental sensing.

Key Features of the MQ-135:

• Gas Detection: The MQ-135 is sensitive to a variety of gases including:
• Ammonia (NH₃)
• Nitrogen Oxides (NOx)
• Benzene (C₆H₆)
• Toluene (C₆H₅CH₃)
• Alcohol (ethanol and isopropyl)
• Carbon dioxide (CO₂)
• Smoke (carbon monoxide)
• This makes it useful in applications related to air quality, home automation, and pollution monitoring.
• Analog Output: The sensor provides an analog output voltage that varies based on the concentration of gases it detects. This can be read by a microcontroller (like an Arduino or Raspberry Pi) to interpret the concentration of gases in the air.
• Heating Element: The MQ-135 contains a heating element and a sensor layer that changes its resistance depending on the concentration of gases in the air. As gases interact with the sensor layer, the resistance changes, and this change is translated into an analog voltage signal.
• Sensitivity Adjustments: It is possible to adjust the sensitivity of the sensor by varying the load resistor (connected to the sensor). This allows for calibration to detect a broader or more focused range of gas concentrations.
• Long Life and High Stability: MQ sensors generally have a long lifespan and provide stable readings once they have warmed up and are calibrated properly.

Working Principle:

• The sensor has a heating element and sensor material that changes resistance in the presence of various gases. When the sensor is exposed to specific gases, the sensor material reacts with the gas molecules, changing its resistance. This change is measured by the output voltage.
• The output of the MQ-135 sensor is an analog signal, which corresponds to the concentration of gases in the air. This signal can be processed by a microcontroller to determine the level of specific gases.

Pinout:

1. VCC: Power supply input (typically 5V).
2. GND: Ground.
3. AOUT: Analog output, which can be read by a microcontroller (e.g., Arduino).
4. DOUT: Digital output (optional), typically used for a threshold-based output where it triggers high or low depending on whether the concentration exceeds a certain threshold (useful for alarm systems).

Applications:

• Air Quality Monitoring: Measure pollution levels in homes, offices, and industrial settings.
• Indoor Air Quality: Monitor gases like ammonia and carbon dioxide in greenhouses, offices, or classrooms.
• Home Automation Systems: Use in smart homes to detect changes in air quality or gas levels and activate systems like air purifiers.
• Safety Systems: Detect gas leaks (e.g., CO, ammonia) to trigger alarms or notifications.

Calibration:

• The MQ-135 sensor often requires initial calibration and a preheating period to stabilize its readings. Typically, it may take 24-48 hours for the sensor to fully stabilize.
• To obtain accurate readings, it is common practice to expose the sensor to a known concentration of the target gases and adjust its readings accordingly.

Example Arduino Code for Reading the MQ-135 Sensor:

Here’s an example of how to use the MQ-135 with an Arduino:

int mq135Pin = A0;  // Analog pin connected to the MQ-135 sensor
int mq135Value = 0; // Variable to store sensor reading

void setup() {
  Serial.begin(9600);  // Start serial communication
}

void loop() {
  mq135Value = analogRead(mq135Pin);  // Read the value from the sensor
  Serial.print("MQ-135 Sensor Value: ");
  Serial.println(mq135Value);  // Print the sensor value
  delay(1000);  // Wait for 1 second
}

In this example:

• The sensor’s analog output is connected to analog pin A0 of the Arduino.
• The analogRead() function reads the sensor's output, which is an analog voltage proportional to the gas concentration.
• The value is then printed to the Serial Monitor for observation.

Important Considerations:

• Preheating: After powering on the sensor, it needs a few minutes to warm up and stabilize its readings.
• Humidity and Temperature: Environmental factors like humidity and temperature can affect the sensor’s performance. Some users use additional sensors (e.g., temperature and humidity sensors) to compensate for these changes.
• Calibration: The sensor should be calibrated periodically to ensure accurate readings, especially if used for critical applications like air quality control or pollution monitoring.

Brand:- Generic

Origin:- China