How to Use mq-137: Examples, Pinouts, and Specs

The MQ-137 is a gas sensor manufactured by HANWEI ELECTRONICS CO., LTD., designed to detect various gases, particularly hydrogen sulfide (H₂S). It operates on the principle of resistive change, where the sensor's resistance varies in the presence of target gases. This analog output can be processed to determine gas concentrations, making the MQ-137 a versatile component for environmental monitoring, industrial safety systems, and air quality control.

• Environmental monitoring systems
• Industrial safety and gas leak detection
• Air quality monitoring in residential and commercial spaces
• Laboratory gas detection setups
• IoT-based gas sensing applications

The MQ-137 sensor is designed for reliable and accurate gas detection. Below are its key technical details:

The MQ-137 sensor typically comes with six pins. Below is the pin configuration and description:

Note: Pins A and B are internally connected, and either can be used for the analog output.

1. Powering the Sensor:

   • Connect the H1 pin to a 5V DC power supply.
   • Connect the H2 pin to ground.
   • Ensure the heater voltage (VH) is stable at 5V ± 0.2V for accurate operation.

2. Connecting the Output:

   • Connect one of the analog output pins (A or B) to the ADC (Analog-to-Digital Converter) input of your microcontroller or data acquisition system.
   • Use a load resistor (RL) between the analog output pin and ground. A typical value for RL is 10 kΩ, but it can be adjusted based on your application.

3. Preheating the Sensor:

   • Allow the sensor to preheat for at least 24 hours before taking measurements. This ensures stable and accurate readings.

4. Reading the Output:

   • The sensor outputs an analog voltage proportional to the concentration of H₂S gas. Use an ADC to convert this voltage into a digital value for further processing.

• Calibration: The MQ-137 requires calibration to accurately map the analog output voltage to gas concentration. Use a known concentration of H₂S gas for calibration.
• Environmental Factors: Avoid exposing the sensor to high humidity, extreme temperatures, or corrosive gases, as these can affect its performance.
• Power Supply Stability: Ensure a stable 5V power supply to avoid fluctuations in the heater voltage, which can impact sensor accuracy.

Below is an example of how to connect and read data from the MQ-137 sensor using an Arduino UNO:

• Connect H1 to the 5V pin on the Arduino.
• Connect H2 to the GND pin on the Arduino.
• Connect one of the analog output pins (A or B) to the A0 pin on the Arduino.
• Place a 10 kΩ resistor between the analog output pin and ground.

// MQ-137 Gas Sensor Example with Arduino UNO
// This code reads the analog output of the MQ-137 and prints the value to the Serial Monitor.

const int sensorPin = A0; // Analog pin connected to MQ-137 output
int sensorValue = 0;      // Variable to store the sensor reading

void setup() {
  Serial.begin(9600); // Initialize serial communication at 9600 baud
  Serial.println("MQ-137 Gas Sensor Test");
}

void loop() {
  sensorValue = analogRead(sensorPin); // Read the analog value from the sensor
  Serial.print("Sensor Value: ");
  Serial.println(sensorValue); // Print the sensor value to the Serial Monitor

  // Add a delay for stability
  delay(1000); // Wait for 1 second before the next reading
}

Note: The raw sensor value must be calibrated to convert it into a gas concentration (ppm). Refer to the sensor's datasheet for the calibration curve.

1. No Output or Fluctuating Readings:

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

2. Inaccurate Readings:

   • Cause: Improper calibration or unstable power supply.
   • Solution: Calibrate the sensor using a known gas concentration and ensure a stable 5V power supply.

3. Sensor Not Responding to Gas:

   • Cause: Sensor may be damaged or exposed to extreme environmental conditions.
   • Solution: Replace the sensor and avoid exposing it to high humidity or corrosive gases.

4. High Power Consumption:

   • Cause: Heater circuit drawing excessive current.
   • Solution: Verify the heater voltage is within the specified range (5V ± 0.2V).

Q1: Can the MQ-137 detect gases other than H₂S?
A1: Yes, the MQ-137 can detect other gases, but it is most sensitive to hydrogen sulfide (H₂S). Refer to the datasheet for cross-sensitivity information.

Q2: How do I calibrate the MQ-137 sensor?
A2: Use a known concentration of H₂S gas and record the sensor's output voltage. Create a calibration curve by plotting the voltage against the gas concentration.

Q3: Can I use the MQ-137 with a 3.3V microcontroller?
A3: The sensor requires a 5V power supply for the heater. However, you can use a voltage divider or level shifter to interface the analog output with a 3.3V microcontroller.

Q4: How long does the MQ-137 last?
A4: The sensor's lifespan depends on usage and environmental conditions. Under normal conditions, it can last several years.

By following this documentation, users can effectively integrate the MQ-137 gas sensor into their projects and ensure reliable performance.