Finding Oxygen and CO2 levels using Arduino

Question

int sensorValue;
int pin8 = 8;
void setup()
{
  Serial.begin(9600);      // sets the serial port to 9600
  pinMode(pin8, OUTPUT);
}

void loop()
{
  sensorValue = analogRead(0);       // read analog input pin 0
  Serial.print(sensorValue, DEC);  // prints the value read
  Serial.println("ppm");
  if (sensorValue > 500) {
    // Activate digital output pin 8 - the LED will light up
    digitalWrite(pin8, HIGH);
  }
  else {
    // Deactivate digital output pin 8 - the LED will not light up
    digitalWrite(pin8, LOW);
  }

  delay(5000);           

How can I determine Co2 and O2 level  using MQ135 with Arduino?

Answer 1

If you're using the sensor for the first time, it's a good practice to leave it powered on for about 24 hours before getting a good read.

just calibrate it to get about 100-150 from analogRead in a good air condition.

normal air returns ~100-150
alcohol returns ~700
lighter gas returns ~750+

you can find the code here.