MQ-135 Gas Sensor Module For NH3, Alcohol, benzene, smoke , CO2 Detector Module

The MQ-135 Air Quality Gas Sensor Module is a versatile and high-sensitivity gas detection module designed to monitor air quality by detecting a wide range of harmful gases and pollutants. Based on the MQ-135 metal oxide semiconductor (MOS) gas sensor, the module is capable of sensing gases such as ammonia (NH₃), benzene, alcohol vapors, smoke, carbon dioxide (CO₂), and other volatile organic compounds (VOCs) present in the surrounding environment. It is widely used in indoor air quality monitoring, environmental pollution detection, industrial safety systems, smart home automation, and IoT-based monitoring applications.

The module provides both analog and digital outputs, allowing it to be easily integrated into various embedded systems. The analog output provides a voltage proportional to the concentration of detected gases, while the digital output is generated when the gas concentration exceeds a user-defined threshold set using the onboard sensitivity adjustment potentiometer. This flexibility makes the module suitable for both continuous gas monitoring and simple gas detection or alarm applications.

Operating from a standard 5V DC supply, the MQ-135 module is fully compatible with Arduino, ESP32, ESP8266, Raspberry Pi (with an external ADC for analog readings), STM32, PIC, AVR, ATmega, NodeMCU, and other popular microcontroller platforms. Its compact PCB design, stable performance, long sensor life, and simple interface make it ideal for students, hobbyists, engineers, researchers, and product developers.

The MQ-135 is widely used in environmental monitoring projects, air purification systems, laboratory experiments, ventilation control systems, and educational electronics where reliable detection of air pollutants is required.

Working Principle

The MQ-135 sensor operates using Metal Oxide Semiconductor (MOS) sensing technology. Inside the sensor, a tin dioxide (SnO₂) sensing layer is heated by an internal heating element. In clean air, the sensing material exhibits a specific electrical resistance.

When gases such as ammonia, alcohol vapors, benzene, smoke, carbon dioxide, or other volatile compounds are present, they interact with the heated sensing surface, causing the sensor's electrical resistance to change. The amount of resistance change depends on the concentration of the detected gases.

The onboard signal conditioning circuit converts this resistance variation into an analog voltage that can be measured by a microcontroller. The onboard comparator also compares the signal with a preset threshold, generating a digital HIGH or LOW output when the gas concentration exceeds the selected level. The detection sensitivity can be adjusted using the onboard potentiometer to suit different applications.

Key Features

High-sensitivity multi-gas detection.

Detects ammonia (NH₃), alcohol vapors, benzene, smoke, carbon dioxide (CO₂), and various volatile organic compounds (VOCs).

Based on the MQ-135 Metal Oxide Semiconductor gas sensor.

Analog output for continuous gas concentration monitoring.

Digital output with adjustable detection threshold.

Onboard sensitivity adjustment potentiometer.

Fast response and recovery time.

Stable and reliable performance.

Long operational lifespan.

Low power consumption.

Compact PCB module.

Built-in power and status indicator LEDs.

Compatible with Arduino, ESP32, ESP8266, Raspberry Pi (with external ADC), STM32, PIC, AVR, ATmega, NodeMCU, and PLC systems.

Suitable for environmental monitoring, automation, and educational projects.

Technical Specifications

Sensor Type: Metal Oxide Semiconductor (MOS)

Sensor IC: MQ-135

Operating Voltage: 5V DC

Output Type: Analog (AO) and Digital (DO)

Detection Method: Gas Concentration Sensing

Detectable Gases: Ammonia (NH₃), Benzene, Alcohol Vapors, Smoke, Carbon Dioxide (CO₂), and Various VOCs

Sensitivity Adjustment: Onboard Potentiometer

Response Time: Fast

Recovery Time: Fast

Power Consumption: Low

Interface: VCC, GND, AO, DO

Operating Temperature: Suitable for standard indoor operating environments

Module Type: Air Quality Gas Sensor

Applications

Indoor air quality monitoring.

Air pollution detection systems.

Smart home automation.

Air purification systems.

Industrial gas monitoring.

Environmental monitoring stations.

Ventilation control systems.

HVAC monitoring.

IoT environmental monitoring.

Laboratory gas detection experiments.

Educational electronics projects.

Robotics and automation.

DIY electronics and prototype development.

Research and testing applications.

Safety and alarm systems.

Package Includes

1 × MQ-135 Air Quality Gas Sensor Module

Note

The MQ-135 is designed for air quality monitoring and relative gas concentration detection rather than precise quantitative gas analysis. The sensor requires an initial preheating (burn-in) period and calibration to achieve stable and reliable readings. Environmental factors such as temperature and humidity may influence sensor performance, so proper calibration is recommended for applications requiring improved measurement accuracy.