How to Use MQ137: Examples, Pinouts, and Specs

The MQ137 is a gas sensor manufactured by MQ Sensors, designed to detect ammonia (NH3) concentrations in the air. It operates on the principle of resistive change, where the sensor's resistance varies in response to the presence of ammonia gas. The MQ137 provides an analog output that can be easily interfaced with microcontrollers and other electronic systems.

• Air quality monitoring systems
• Industrial ammonia gas leak detection
• Agricultural applications (e.g., monitoring ammonia levels in livestock environments)
• Environmental monitoring
• Laboratory gas detection systems

The MQ137 sensor is designed for reliable and accurate ammonia gas detection. Below are its key technical details:

The MQ137 sensor module typically comes with a 4-pin interface. Below is the pin configuration:

The MQ137 sensor is straightforward to use in a circuit. Follow the steps below to integrate it into your project:

1. Power the Sensor: Connect the VCC pin to a 5V DC power supply and the GND pin to ground.
2. Connect the Output:
   • Use the AOUT pin to read the analog signal corresponding to ammonia concentration.
   • Optionally, use the DOUT pin for a digital signal if a threshold is set using the onboard potentiometer.
3. Preheat the Sensor: Allow the sensor to preheat for at least 24 hours before taking accurate measurements. This stabilizes the internal heater and sensing element.
4. Read the Output:
   • For analog readings, connect the AOUT pin to an analog input pin on a microcontroller (e.g., Arduino).
   • For digital readings, connect the DOUT pin to a digital input pin.

• Preheat Time: Ensure the sensor is preheated for at least 24 hours for optimal accuracy.
• Calibration: Calibrate the sensor in a known ammonia concentration environment to improve accuracy.
• Ventilation: Use the sensor in a well-ventilated area to avoid saturation or false readings.
• Load Resistance: Adjust the load resistance (RL) to match your application requirements.
• Avoid Contaminants: Keep the sensor away from water, oil, and other contaminants that may damage it.

Below is an example of how to interface the MQ137 with an Arduino UNO to read analog values:

// MQ137 Gas Sensor Example Code
// This code reads the analog output of the MQ137 sensor and prints the value
// to the Serial Monitor. Ensure the sensor is preheated for accurate readings.

const int MQ137_AOUT = A0; // Connect AOUT pin of MQ137 to Arduino A0 pin

void setup() {
  Serial.begin(9600); // Initialize serial communication at 9600 baud
  pinMode(MQ137_AOUT, INPUT); // Set AOUT pin as input
}

void loop() {
  int sensorValue = analogRead(MQ137_AOUT); // Read analog value from MQ137
  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
}

1. No Output or Incorrect Readings:

   • Cause: Insufficient preheat time.
   • Solution: Ensure the sensor is preheated for at least 24 hours before use.

2. Fluctuating Readings:

   • Cause: Unstable power supply or environmental interference.
   • Solution: Use a stable 5V DC power source and avoid placing the sensor near strong electromagnetic fields.

3. Sensor Saturation:

   • Cause: Exposure to high ammonia concentrations for extended periods.
   • Solution: Allow the sensor to recover in clean air before reuse.

4. No Digital Output:

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

Q1: Can the MQ137 detect gases other than ammonia?
A1: While the MQ137 is optimized for ammonia detection, it may respond to other gases. However, its sensitivity and accuracy for non-ammonia gases are not guaranteed.

Q2: How do I calibrate the MQ137 sensor?
A2: To calibrate the sensor, expose it to a known concentration of ammonia gas and adjust the load resistance (RL) or use software calibration to map the analog output to the gas concentration.

Q3: Can I use the MQ137 with a 3.3V microcontroller?
A3: The MQ137 requires a 5V power supply for its heater. However, you can use a voltage divider or level shifter to interface its output with a 3.3V microcontroller.

Q4: How long does the MQ137 sensor last?
A4: The sensor's lifespan depends on usage and environmental conditions. Under normal conditions, it can last several years with proper care and maintenance.