MQ135 GAS SENSOR

Updated and improved Arduino library for the MQ135 gas/air quality sensor.

This library is also available in the Arduino IDE, see Arduino Library List.

Datasheet

Can be found here.

Application

This type of sensor is used in air quality control equipments for buildings/offices and is suitable for detecting of NH3, NOx, alcohol, Benzene, smoke, CO2, etc.

Features

This library has:

• Corrections for temperature and humidity
• Measurements:
  • getResistance
  • getCorrectedResistance
  • getPPM
  • getCorrectedPPM
  • getRZero
  • getCorrectedRZero

Calibration

To get an accurate ppm reading it is important to calibrate the sensor.

To do so put your sensor outside where there is enough fresh air (ideally at 20°C & 33% humidity according to the datasheet) and leave it powered on for 12-24 hours to burn it in and stabilize.

Then you can read out the calibrated resistance value RZERO like this (needs to be done when still outside!):

float rzero = gasSensor.getRZero();

The best way to do this is to average multiple readings to fight ADC noise. To finish the calibration process you now only need to pass your RZERO value to the constructor like this:

MQ135 gasSensor(PIN_MQ135, RZERO);

More Info

https://hackaday.io/project/3475-sniffing-trinket/log/12363-mq135-arduino-library