“The MQ-135 Gas sensor can detect gases like Ammonia (NH3), sulfur (S), Benzene (C6H6), CO2, and other harmful gases and smoke. Similar to other MQ series gas sensor, this sensor also has a digital and analog output pin. When the level of these gases go beyond a threshold limit in the air the digital pin goes high. This threshold value can be set by using the on-board potentiometer. The analog output pin, outputs an analog voltage which can be used to approximate the level of these gases in the atmosphere.The MQ135 air quality sensor module operates at 5V and consumes around 150mA. It requires some pre-heating before it could actually give accurate results. The MQ135 is one of the popular gas sensors from the MQ series of sensors that are commonly used in air quality control equipment. It operates from 2.5V to 5.0V and can provide both digital and analog output.

– Technical Specifications of MQ135 Gas Sensor:
– Operating Voltage: 2.5V to 5.0V.
– Power consumption: 150mA.
– Detect/Measure: NH3, Nox, CO2, Alcohol, Benzene, Smoke.
– Typical operating Voltage: 5V.
– Digital Output: 0V to 5V (TTL Logic ) @ 5V Vcc.
– Analog Output: 0-5V @ 5V Vcc” “Good sensitivity towards harmful gases with a wide range of concentrations

Long lifespan and low cost
Simple driving circuit
High sensitivity towards ammonia gas, sulfide, and benzene series vapor
Also suitable for detecting smoke and other harmful substances
Can be used in household air pollution alarms, industrial air pollution controllers, and portable air pollution detectors.”