How to Use MQ-137 SENSOR AMMONIA GAS: Examples, Pinouts, and Specs

The MQ-137 is an analog gas sensor module used for the detection of ammonia (NH3) in the air. It is a widely used sensor in various applications such as environmental monitoring, agricultural, industrial processes, and safety systems where the presence of ammonia needs to be detected and measured.

• Air quality monitoring
• Industrial leak detection
• Agricultural monitoring for livestock environments
• Refrigeration systems
• Safety systems in chemical plants

• Detection Gas: Ammonia (NH3)
• Concentration Range: 5 ppm to 500 ppm
• Supply Voltage (Vcc): 5V ± 0.1
• Heater Voltage (VH): 5V ± 0.1
• Heater Current: Less than 180 mA
• Load Resistance: Adjustable
• Preheat Duration: 20 minutes
• Output: Analog voltage signal output

1. Powering the Sensor: Connect the VCC pin to a 5V supply and the GND pin to the ground.
2. Analog Output: Connect the AO pin to an analog input on your microcontroller to read the analog voltage corresponding to the concentration of ammonia.
3. Digital Output: The DO pin can be connected to a digital input on your microcontroller. It can be used to trigger an action when the gas concentration exceeds a certain threshold, which can be set using the onboard potentiometer.

• Ensure the sensor is preheated for at least 20 minutes before taking accurate readings.
• Avoid exposure to high concentrations of ammonia for extended periods as it may lead to sensor degradation.
• Calibrate the sensor for the environment in which it will be used to ensure accurate readings.
• The sensor's sensitivity varies with temperature and humidity, so these factors should be considered during use.

• Inaccurate Readings: Ensure the sensor is properly calibrated and has been preheated.
• No Output Signal: Check the power supply and connections to the sensor.
• Sensor Not Responding: The sensor may be damaged due to high gas concentrations or incorrect voltage application.

• Calibration: Perform regular calibration using a known concentration of ammonia to maintain accuracy.
• Connection Check: Verify all connections are secure and the power supply is within the specified range.
• Sensor Replacement: If the sensor has been exposed to high concentrations of ammonia or has been in use for an extended period, consider replacing it.

// MQ-137 Ammonia Gas Sensor Example Code
const int analogPin = A0; // Analog input pin connected to AO pin of the sensor

void setup() {
  Serial.begin(9600); // Initialize serial communication at 9600 baud rate
}

void loop() {
  int sensorValue = analogRead(analogPin); // Read the analog value from sensor
  float concentration = sensorValue * (10.0 / 1023.0); // Convert to concentration
  // Note: The conversion factor will vary depending on calibration

  Serial.print("Ammonia Concentration: ");
  Serial.print(concentration);
  Serial.println(" ppm");
  delay(1000); // Wait for a second before reading again
}

Note: The above code is a simple example to read the analog value from the MQ-137 sensor. The conversion from the analog value to the actual concentration in ppm requires calibration with a known ammonia concentration. The 10.0 / 1023.0 factor is an example and should be replaced with the appropriate calibration factor for your specific setup.

Remember to keep code comments concise and within the 80 character line length limit.