Carbon Monoxide Detection with MQ-9

Objective

The goal of this experiment is to use the MQ-9 gas sensor to measure and monitor carbon monoxide (CO) levels in the air, displaying the data in real-time on a serial monitor. This project can serve as a foundation for creating CO detection systems for safety applications.

Required Components

• MQ-9 Gas Sensor
• Arduino Board (e.g., Arduino Uno)
• Jumper wires
• Breadboard
• USB cable for Arduino
• Optional: OLED display or LCD for real-time CO level display
• Computer with Arduino IDE installed

Ensure the MQ-9 sensor module includes the required pull-up resistors, or you may need to add them externally for proper functionality.

Working Principle

The MQ-9 gas sensor detects gases by using a chemical sensing element. When carbon monoxide or combustible gases are present, they interact with the tin dioxide (SnO₂) material inside the sensor, causing its resistance to change. This change is translated into an analog voltage that the Arduino reads to determine gas concentration.

Key features of the MQ-9 sensor:

• High sensitivity to carbon monoxide and methane gases.
• Fast response time and low power consumption.
• Operates within a wide range of temperatures and humidity levels.

Circuit Wiring

Follow the steps below to connect the MQ-9 gas sensor to the Arduino board:

• Connect the VCC pin of the MQ-9 sensor to the 5V pin of the Arduino.
• Connect the GND pin of the MQ-9 sensor to the GND pin of the Arduino.
• Connect the AOUT (analog output) pin of the MQ-9 sensor to the A0 analog pin of the Arduino.
• If using the DOUT (digital output) pin, connect it to a digital pin on the Arduino (optional, for threshold-based detection).

Ensure all connections are secure and avoid short circuits by using a breadboard and jumper wires.

Sensor Calibration

The MQ-9 sensor requires calibration to ensure accurate measurements. Calibration involves exposing the sensor to a known concentration of carbon monoxide and adjusting the output values to match the reference levels.

Steps for basic calibration:

• Power on the sensor for 24-48 hours (preheating phase) to stabilize its readings.
• Expose the sensor to clean air and record the analog output value (this represents the base resistance).
• Expose the sensor to a known concentration of CO gas and record the output value.
• Calculate the ratio of gas resistance (R_gas) to air resistance (R_air) to fine-tune the Arduino code for accurate readings.

Arduino Code

/*
 * Carbon Monoxide Detection using MQ-9
 * This code reads the carbon monoxide concentration from the MQ-9 sensor.
 */

const int sensorPin = A0;  // MQ-9 sensor connected to analog pin A0
int sensorValue = 0;

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

void loop() {
  sensorValue = analogRead(sensorPin);  // Read the sensor value
  float voltage = sensorValue * (5.0 / 1023.0); // Convert to voltage
  Serial.print("Analog Value: ");
  Serial.print(sensorValue);
  Serial.print(" | Voltage: ");
  Serial.print(voltage);
  Serial.println(" V");
  delay(1000);  // Wait for 1 second before the next reading
}
            

Note: Modify the code to include calibration data for more accurate gas concentration readings.

Results

The serial monitor will display the raw analog values and converted voltage output from the MQ-9 sensor. These values can be used to estimate carbon monoxide concentration after calibration.

Sample Output:

Analog Value: 512 | Voltage: 2.50 V
Analog Value: 530 | Voltage: 2.59 V
            

Limitations

While the MQ-9 sensor is versatile, it has some limitations:

• Requires a long preheating time for accurate readings.
• Sensitivity can be affected by temperature and humidity.
• Cannot distinguish between different combustible gases.
• May require periodic recalibration for consistent performance.

Applications

• Home and industrial safety systems for CO detection.
• Air quality monitoring in enclosed spaces.
• Vehicle exhaust and emission monitoring systems.
• Smart IoT devices for environmental monitoring.

Conclusion

The MQ-9 sensor is an effective tool for detecting carbon monoxide and other combustible gases, offering a cost-effective solution for building safety and environmental monitoring systems. With proper calibration, it can provide reliable measurements for various applications.