MQ-135 Air Quality Gas Sensor Module – NH3, CO2, Benzene, Smoke Detector (LM393, Digital & Analog Output)

MQ-135 Air Quality Gas Sensor Module – NH3, CO2, Benzene & Smoke Detector

The MQ-135 Gas Sensor Module is a versatile, multi-gas detection module from the popular MQ series of electrochemical gas sensors. It is capable of detecting a wide range of harmful gases including Ammonia (NH3), Nitrogen Oxides (NOx), Carbon Dioxide (CO2), Alcohol, Benzene (C6H6), and Smoke — making it a go-to choice for air quality monitoring, indoor pollution detection, and industrial safety systems.

The module operates between 2.5V and 5.0V (typically at 5V) and exposes both a Digital Output (TTL) and an Analog Output (0–5V). The digital pin is driven by an onboard LM393 Op-Amp Comparator IC that compares the live sensor reading against a threshold set by the onboard 10K potentiometer. When gas levels exceed the threshold, the digital output goes LOW and the D0 indicator LED illuminates — enabling standalone gas alert operation without any microcontroller.

For precise PPM (Parts Per Million) measurement, the analog output pin can be read by a microcontroller like Arduino. The analog voltage reflects the ratio of Rs/Ro (sensor resistance in gas vs. clean air), which can be mapped against the MQ-135 datasheet sensitivity curve to derive accurate gas concentration values. A pre-built MQ-135 Arduino Library is available to simplify this calculation.

⚠️ Important: Like all MQ series sensors, the MQ-135 requires a pre-heat duration of 30 seconds to 2 minutes after power-up for the sensing element to warm up and provide stable, accurate readings. The Power LED will turn on during this period — simply wait before taking measurements.

🔧 Key Features

• Target Gases: NH3, NOx, CO2, Alcohol, Benzene (C6H6), Smoke.
• Operating Voltage: 2.5V – 5.0V DC (Typical: 5V).
• Power Consumption: 150mA.
• Digital Output: TTL logic, 0V – 5V (Active LOW on gas detection).
• Analog Output: 0V – 5V (proportional to gas concentration).
• Comparator IC: LM393 Op-Amp (onboard).
• Sensitivity Adjustment: Onboard 10K potentiometer.
• Indicator LEDs: Power LED + D0 gas detection LED.
• Standalone Operation: Yes — digital output can directly drive a buzzer or LED via transistor.
• PPM Measurement: Yes — via analog pin with Arduino and MQ-135 library.
• Pre-Heat Time: 30 seconds to 2 minutes.
• Compatibility: Arduino, ESP32, ESP8266, NodeMCU, PIC, ARM, STM32, Raspberry Pi.

💡 Applications

• Indoor air quality monitoring systems.
• Smart home and IoT gas alert systems.
• Industrial and workplace harmful gas detectors.
• CO2 and ammonia level monitoring in greenhouses and farms.
• Air pollution detection in Arduino and ESP32 projects.
• School and college STEM/science project demonstrations.
• Smoke and alcohol detection in safety enclosures.

⚙️ Technical Specifications Summary

📦 Package Includes

• 1 × MQ-135 Air Quality Gas Sensor Module

Further Resources: MQ-135 Datasheet | MQ-135 Arduino Library | Interfacing MQ-135 with Arduino Tutorial — available on the product page.