MQ135 output on Arduino Uno

Question

I bought an FC-22 (MQ135) gas sensor module which I plugged into my Arduino Uno. I connected it to the A0 analog port. Then created a code that reads the raw data from A0 (code below).

When I run the code on my Arduino Uno in my house I get values of about 30. If I blow over the sensor I get values until about 160. My question is now how I have to read / interpret these values.

According to the MQ135 specifications the sensor has a sesitivity for air quality, measuring benzene, alcohol and smoke.

How can I interpret the values I get? What is a good value and what isn't? Do I have to calculate something out of these values?

My code looks like this:

void setup() {
 Serial.begin(9600);
 pinMode(13, OUTPUT);
}
void loop() {
 int sensorValue = analogRead(0);
 Serial.print(sensorValue, DEC);
 delay(100);
 if (sensorValue > 50) {
 digitalWrite(13, HIGH);
 }
 else {
 digitalWrite(13, LOW);
 }
}

• manish: any reference for co2 calibration?
• Socrates: @manish As for now the only info I have is from the answer below in the datasheet of the MQ135.

Answer 1

According to the datasheet you have to calibrate it.

• Socrates: Thanks for the link to the datasheet. Yep, at the end of the document indeed it says to calibrate the sensor to either 100ppm NH3 or 50ppm Alcohol. Unfortunately, I haven't got the tools to create an atmosphere with these contents. Furthermore, I'd be more interested in CO2 values, even if I didn't state that in the initial question.
• Aditya Ponkshe: @Socrates Any update on CO2? I'm struggling with it. Could you please help me out?
• Socrates: @AdityaPonkshe I haven't got any update on this yes, sorry. Please post it here, if you get it running.