How to Use MQ-136 SENSOR HYDROGEN SULFIDE GAS: Examples, Pinouts, and Specs

The MQ-136 Hydrogen Sulfide (H2S) Gas Sensor is an electronic device used to measure the concentration of hydrogen sulfide gas in the air. This sensor is widely used in industrial applications, environmental monitoring, and safety systems where the presence of H2S, a toxic and corrosive gas, needs to be detected and measured.

• Industrial safety systems to detect gas leaks
• Environmental monitoring for air quality
• Laboratory research and analysis
• Mining operations where H2S is a byproduct
• Sewage treatment plants for odor control monitoring

• Sensor Type: Semiconductor
• Detection Gas: Hydrogen sulfide (H2S)
• Concentration Range: 1 ppm to 10 ppm (parts per million)
• Supply Voltage (Vcc): 5V ± 0.1V DC
• Output Voltage (VRL): 0.1 - 0.3V (in clean air)
• Preheat Duration: 20 minutes (minimum)
• Load Resistance: Adjustable via onboard potentiometer
• Operating Temperature: -20°C to 50°C
• Relative Humidity: 95% RH non-condensing

1. Connect the VCC pin to a 5V power supply.
2. Connect the GND pin to the ground of the power supply.
3. The AOUT pin provides an analog voltage output that is proportional to the concentration of H2S gas. Connect this to an analog input on your microcontroller.
4. The DOUT pin provides a digital signal when the concentration of H2S exceeds a certain threshold. This threshold can be adjusted using the onboard potentiometer.

• Ensure the sensor is preheated for at least 20 minutes before taking accurate readings.
• Avoid exposure to high concentrations of organic solvents, silicon compounds, and sulfur which can poison the sensor.
• Calibrate the sensor periodically to maintain accuracy.
• Implement proper ventilation when using the sensor to prevent accumulation of gases.

// MQ-136 Hydrogen Sulfide Gas Sensor Example Code
const int ANALOG_PIN = A0; // Analog input pin connected to AOUT on the sensor
const int DIGITAL_PIN = 2; // Digital input pin connected to DOUT on the sensor

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

void loop() {
  int sensorValue = analogRead(ANALOG_PIN); // Read the analog value from sensor
  int digitalValue = digitalRead(DIGITAL_PIN); // Read the digital value from sensor

  // Print the analog value to the serial monitor
  Serial.print("Analog H2S Value: ");
  Serial.println(sensorValue);

  // Print the digital status to the serial monitor
  Serial.print("Digital H2S Status: ");
  Serial.println(digitalValue ? "HIGH" : "LOW");

  delay(1000); // Wait for 1 second before the next loop
}

• Inaccurate Readings: Ensure the sensor is properly preheated and calibrated.
• No Output Signal: Check the power supply and connections to the sensor.
• Sensor Poisoning: Avoid exposure to high concentrations of pollutants.

• Preheat the Sensor: Always preheat the sensor for at least 20 minutes before use.
• Calibration: Perform regular calibration using known H2S concentrations.
• Check Connections: Ensure all connections are secure and free from corrosion.

• Q: How often should the sensor be calibrated?
  • A: Calibration frequency depends on usage, but typically every 6 months is recommended.
• Q: Can the sensor detect other gases?
  • A: The MQ-136 is specific to hydrogen sulfide but may show cross-sensitivity to other gases.
• Q: What is the lifespan of the sensor?
  • A: With proper use and maintenance, the sensor can last up to 2 years.

This documentation provides a comprehensive guide to using the MQ-136 Hydrogen Sulfide Gas Sensor. For further assistance, please refer to the manufacturer's datasheet or contact technical support.