The MQ-135 sensor module is based on the MQ135 sensor that provides a lower conductivity to clean the air as a gas sensing material. MQ135 sensor is ideal for detection or measuring of NH3, Sulphide, and Benzene steam, smoke, and other harmful gases. It offers very good sensitivity and a fast response time makes it ideal such as used in air quality control types of equipment. When the sensor is kept in the environment, the conductivity increases with respect to the rise in the concentration of gases. The module comes with basic components integrated allowing the sensor to function properly. And can be interfaced easily to any controller as the user prefers. The MQ135 air quality sensor module operates at a voltage of 5V and consumes around 150mA.
MQ135 module consists of both digital and analogue outputs. This module not only provides a binary indication of the presence of combustible gases but also an analogue representation of their concentration in air. When gas is detected using the digital output, the indicator LED D0 turns ON and the digital pin will go from logic high to logic low 0V. LM393 Op-Amp Comparator IC was used to compare the actual gas value with the value set using the potentiometer. The presence of onboard LM393 comparator IC in the MQ135 module also eliminates the need for an external microcontroller. Simply power up the module and set the sensitivity of the digital pin using the potentiometer. So when the module detects the gas the digital pin will go low.
While using the analogue pin, the analogue values (0-5V) are read using a microcontroller, that calculates the resistance value. By using the external load resistance the resistance variation is converted into a suitable voltage variation. This will be directly proportional to the concentration of the gas to which the sensor detects.