MikroElektronika Forum

Hi!

I am very interested in air quality measurements with MQ-135 sensor (Air Quality Click board). My approach was to measure voltage on sensor and to calculate sensor's resistance in aim to estimate if VOC level increases or decreases because "The MQ-135 sensor unit has a sensor layer made of tin dioxide (SnO2), an inorganic compound which has lower conductivity in clean air than when polluting gases are present."

Is this very good approximation based on experience and experiments which can be used for ppm calculation or it is just example how to do math is Ro is known.

Thanks.

Hi,

Welcome to the mikroE forum.

There is a function named airquality_getResistance in the Air Quality click library, you just need to call it with ADC_Value parameter and it will return a resistance value.
You can find the formula for calculating PPM value in the following links:
https://github.com/MikroElektronika/Air ... y_driver.c
https://community.particle.io/t/mq135-c ... tion/24061

Kind regards,

Hi,

Welcome to the MikroE forum.

Air quality click is suitable for detecting ammonia (NH3), nitrogen oxides (NOx) benzene, smoke, CO2 and other harmful or poisonous gases that impact air quality. The MQ-135 sensor unit has a sensor layer made of tin dioxide (SnO2), an inorganic compound which has lower conductivity in clean air than when polluting gases are present.

For more information about the MQ-135 sensor itself, please refer to its datasheet.

Kind regards,