MQ135 is an Air Quality Sensor suitable for detecting of NH3, Alcohol, Benzene and other gases. The description below, is what i derive from the poor datasheet of this sensor, it may be uncorrect, so if you have suggestions please leave me a feedback. update - Here you can find a way to estimate the correlation function of MQ sensors, and extrapolate coefficients from the datasheet curves: http://
![Cheap CO2 meter using the MQ135 sensor with AVR ATmega](https://cdn-ak-scissors.b.st-hatena.com/image/square/54d7fdbaff1c7f31affa995fe5e338fe9d4b3468/height=288;version=1;width=512/https%3A%2F%2Fblogger.googleusercontent.com%2Fimg%2Fb%2FR29vZ2xl%2FAVvXsEig2zdb4wmt0AHYjCfNoRvFFgh-VRBceacw0ASVtaxA-V_x_4Tx5sTF-hnQDkTfaevuLQ-WzBaCnb5ThRFZVTld2SMtdYMpT-sdmXOmVWsApRA7eFWQBWoa2KoAMhk6JRA07GGrayJ4NJI%2Fw1200-h630-p-k-no-nu%2Fmq135_pinout.jpg)