MQ135 Air Quality Sensor : Pin Configuration, Working & Its Applications

A wide variety of gases, including NH₃, NO_x, alcohol, benzene, smoke, and CO₂, can be detected by the MQ135 Gas Sensor, an air quality sensor. Perfect for usage in a factory or office. The MQ135 gas sensor is very sensitive to hazardous gases like smoke and ammonia, sulfide, and benzene steam.

The MQ135 gas sensor’s sensitive component is SnO₂, which has a reduced conductivity in clean air. The conductivity of the sensor increases as the concentration of the target pollutant gas increases. Through a straightforward circuit, users can translate the change in conductivity to the corresponding output signal of gas concentration.
The MQ135 gas sensor is very sensitive to harmful gases like smoke and ammonia, hydrogen sulfide, and benzene series steam. It is a type of inexpensive sensor for various applications and is capable of detecting various harmful gases.

Pin Configuration of MQ135 Air Quality Sensor

One of the well-known gas sensors from the MQ series that is frequently utilized in air quality control equipment is the MQ135. It is functional between 2.5V and 5.0V and can produce both digital and analog signals. Below is a list of the pinouts and significant parts of an MQ135 Module.

VCC – 2.5V to 5V

GND – Ground

D0 – Digital output

A0 – Analog output

This sensor, like the others in the MQ series of gas sensors, has a pin for both digital and analog output. The digital pin turns high when the amount of these gases in the air exceeds a predetermined threshold. The onboard potentiometer can be used to adjust this threshold value. An analog voltage that is produced by the analog output pin can be used to approximatively determine the concentration of various gases in the atmosphere.

The above fig is the basic test circuit of MQ135. The sensor requires two voltage inputs: heater voltage (VH) and circuit voltage(VC). VH is used to supply standard working temperature to the sensor and it can adopt DC or AC power, while VRL is the voltage of load resistance RL which is in series with the sensor. VC supplies the detect voltage to load resistance RL and it should adopt DC power.
Keep in mind that all MQ sensors must be powered on for a pre-heat period before they can begin to function. Typically, this pre-heat period lasts from a few seconds to a few minutes. The power LED will turn on when you turn on the module; keep it in this mode until the pre-heat period is finished.

It is widely used in domestic gas alarms, industrial gas alarms, and portable gas detectors.
One other industry that utilizes gas sensing technologies tremendously is the medical and life science fields.
Aerospace environments utilize gas sensors specifically to monitor for in-flight conditions and air quality maintenance to ensure crew productivity, as well as overall passenger comfort.
When it comes to finding the perfect sensing solution for agriculture applications, it is most common for those individuals looking to measure carbon dioxide in terms of maximizing plant yields.
Modified Atmospheric Packaging (MAP) has become more prevalent in the last decade due to the demand for a longer shelf life of perishable products.
In the last 5 to 10 years, the transportation industry has actively sought new sensor technology. These sectors frequently examine carbon dioxide and oxygen levels in cargo, such as dry ice shipment, or examine shipping containers to keep an eye on product spoilage.