MQ135 Air Quality Sensor

				
					/*
  MQ135 Air Quality Sensor Example
  --------------------------------
  This example reads the analog output (AO) from an MQ135 gas sensor
  and converts it into a voltage value. The MQ135 can detect gases
  such as CO2, NH3, benzene, alcohol, and smoke.

  Hardware:
  - MQ135 sensor module
  - Arduino UNO or compatible board
  - Connect AO pin to Arduino analog pin A0
  - Connect VCC to 5V
  - Connect GND to GND
*/

const int mq135Pin = A0;  // Analog input pin connected to MQ135 AO
float sensorValue = 0;    // Variable to store the ADC reading
float voltage = 0;        // Converted voltage value

void setup() {
  Serial.begin(9600);     // Start serial communication
  Serial.println("MQ135 Air Quality Sensor Test");
  delay(2000);            // Warm-up delay (sensor needs a few seconds to stabilize)
}

void loop() {
  // Read the analog input (0–1023 for 10-bit ADC)
  sensorValue = analogRead(mq135Pin);

  // Convert ADC value to voltage (assuming 5V reference)
  voltage = sensorValue * (5.0 / 1023.0);

  // Print results to serial monitor
  Serial.print("Raw value: ");
  Serial.print(sensorValue);
  Serial.print(" | Voltage: ");
  Serial.print(voltage);
  Serial.println(" V");

  /*
    Note:
    - To convert voltage to ppm (gas concentration), you need to
      calibrate the sensor and use the appropriate formula or curve
      from the MQ135 datasheet.
    - Example (pseudo):
        float ratio = (R0 / Rs);
        float ppm = pow(10, ((log10(ratio) - b) / m));
      where m and b come from the gas curve for a specific gas.
  */

  delay(1000);  // Read every 1 second
}