MQ9 CO Carbon Monoxide and Combustible Gas Sensor

Description

The MQ9 Gas Sensor is a versatile sensor designed to detect carbon monoxide (CO) and combustible gases, such as methane (CH₄) and LPG. It is ideal for applications like gas leak detection, air quality monitoring, and industrial safety systems.

Key Features

• Dual sensitivity for carbon monoxide (CO) and combustible gases.
• Analog and digital outputs for flexible interfacing.
• Adjustable sensitivity using a built-in potentiometer.
• Cost-effective and compact design.

Specifications

• Operating Voltage: 5V DC
• Operating Current: ~150 mA
• Detectable Gases: Carbon monoxide (CO), methane (CH₄), LPG, and other combustible gases.
• Output Types:
  • Analog Output (AO): Proportional to gas concentration.
  • Digital Output (DO): HIGH/LOW signal based on the threshold set by the potentiometer.
• Detection Range: 10 ppm to 1000 ppm (CO), 100 ppm to 10,000 ppm (CH₄, LPG).
• Preheat Time: ~60 seconds for stable operation.
• Operating Temperature: -10°C to 50°C.

Pinout

1. VCC: Power supply (5V)
2. GND: Ground
3. DO: Digital output
4. AO: Analog output

Working Principle

The MQ9 sensor uses a SnO₂ (tin dioxide) sensing layer. It operates in two modes to optimize detection:

• High-temperature mode (5V): Detects combustible gases such as methane and LPG.
• Low-temperature mode (1.5V): Detects carbon monoxide (CO) more effectively.

The resistance of the sensing material changes based on the concentration of gases, allowing the sensor to measure the gas levels in the environment.

Interfacing with Arduino

Hardware Setup

1. Connect VCC to the Arduino’s 5V pin.
2. Connect GND to the Arduino’s GND pin.
3. Connect AO (Analog Output) to an analog input pin (e.g., A0).
4. (Optional) Connect DO (Digital Output) to a digital input pin for threshold-based detection.

Sample Code

const int analogPin = A0; // Analog output pin
const int digitalPin = 2; // Digital output pin
int analogValue = 0;

void setup() {
  Serial.begin(9600);
  pinMode(digitalPin, INPUT);
}

void loop() {
  // Read analog value
  analogValue = analogRead(analogPin);
  
  // Print analog value (gas concentration)
  Serial.print("Analog Value: ");
  Serial.println(analogValue);

  // Check digital output
  if (digitalRead(digitalPin) == HIGH) {
    Serial.println("Gas concentration exceeded threshold!");
  }
  
  delay(1000);
}

Calibrating the Sensor

1. Preheating: Allow the sensor to preheat for at least 24 hours before calibration.
2. Threshold Adjustment: Use the built-in potentiometer to set the desired digital detection threshold.
3. Heating Voltage Cycling: Implement a heating voltage cycle for optimized gas detection:
   • High Voltage (5V): For combustible gases (e.g., CH₄, LPG).
   • Low Voltage (1.5V): For carbon monoxide (CO).
4. Calibration Curve: Expose the sensor to known gas concentrations and map the analog values to actual gas levels.

Applications

• Carbon Monoxide Detectors: Detecting dangerous CO levels in homes or workplaces.
• Combustible Gas Leak Detection: Monitoring methane, LPG, or other flammable gases.
• Air Quality Monitoring: Evaluating CO and combustible gas concentrations in various environments.
• Industrial Safety Systems: Ensuring safety in factories where combustible gases are used.
• Automotive Systems: Detecting exhaust gases and monitoring air quality inside vehicles.