MQ135 Air Quality Gas Sensor Module

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.
• Details of MQ135 Sensor 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.
• The pinouts and important components on an MQ135 Module is marked below Note that all MQ sensors have to be powered up for a pre-heat duration for the sensor to warm up before it can start working.
• This pre-heat time is normally between 30 seconds to a couple of minutes.
• When you power up the module the power LED will turn on, leave the module in this state till the pre-heat duration is completed.
• 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 Detect Harmful Gases using Digital Pin: The digital output pin of the sensor can be used to detect harmful gases in the environment.
• The sensitivity of the digital pin can be controlled by using the 10k potentiometer.
• If the gas is detected the indicator LED D0 will turn on and the digital pin will go from logic high to logic low (0V).
• The LM393 Op-Amp Comparator IC is used to compare the actual gas value with the value set using the potentiometer.
• If the actual gas value increases than the set value then the digital output pin gets low.
• Because of the onboard LM393 comparator IC the MQ135 Gas sensor module can also be used without the need of an external microcontroller.
• Simply power up the module and set the sensitivity of the digital pin using the potentiometer, then when the module detects the gas the digital pin will go low.
• This digital pin can directly be used to drive a buzzer or LED with the help of simple transistors.
• Measure PPM Value using Analog Pin: The Analog output pin of the sensor can be used to measure the PPM value of the required gas.
• To do this we need to use an external microcontroller like Arduino.
• The microcontroller will measure the value of analog voltage and perform some calculations to find the value of Rs/Ro where Rs is the sensor resistance when gas is present and Ro is sensor resistance at clean air.
• Once we find this ratio of Rs/Ro we can use it to calculate the PPM value of required gas using the graph below which is taken from the datasheet of MQ135 Sensor.
• If you are just detecting the gas and not measuring the PPM then the module need not be calibrated or pre-heated and hence it is extremely simple to use.
• You can find these MQ Gas sensors commonly used in Gas/Smoke detectors and Air Quality Monitors.
• The dimensions of the MQ135 Gas sensor module is given below Further Resources: Datasheet of MQ135 MQ-135 Arduino Library Interfacing MQ135 with Arduino.