MQ-135 Air Quality and Hazardous Gas Sensor Module | Pro Tronix

Product Description

A highly versatile air quality monitoring sensor module designed to detect a wide range of harmful gases and pollutants in Arduino, ESP32, and smart home automation projects. The MQ135 module utilizes a tin dioxide ($\text{SnO}_2$) semiconductor layer that experiences changes in electrical conductivity when exposed to target gases. It is highly sensitive to Ammonia ($\text{NH}_3$), Benzene, alcohol, smoke, Carbon Dioxide ($\text{CO}_2$), and other harmful environmental vapors. Featuring both an analog output for real-time concentration tracking and a digital threshold output controlled by an onboard potentiometer, this module is an essential component for building DIY air purifiers, indoor pollution monitors, and smart ventilation systems.

Pinout / Layout Connections

The module breaks out its tracking interface via a standard 4-pin male header block:

• • VCC Pin: Power supply input, requires a stable DC +5V. (Critical: The internal heating element requires substantial current, so power it from a robust 5V source rather than low-current pins).

  • GND Pin: Common system ground (0V) reference.

  • DO (Digital Output) Pin: Digital threshold pin. Outputs a HIGH/LOW logic signal when gas concentration passes the limit set by the onboard potentiometer.

  • AO (Analog Output) Pin: Analog output pin. Generates a variable voltage ($0\text{V}$ to $5\text{V}$) directly proportional to the detected gas concentration level.