The MQ135 Air Quality and Hazardous Gas Sensor Module is a critical component for monitoring atmospheric health and safety. At Electrapac, we recommend this sensor for environmental enthusiasts and engineers building smart ventilation systems, indoor air quality (IAQ) monitors, or pollution-tracking IoT devices.

The MQ135 is a Metal Oxide Semiconductor (MOS) sensor specifically designed to detect a wide array of air pollutants. It is particularly sensitive to Ammonia ($N{H}_3$), Nitrogen Oxides ($N{O}_x$), Alcohol, Aromatic compounds (Benzene), Sulfide, and Smoke. While it is often used for relative $C{O}_2$ (Carbon Dioxide) detection in indoor environments, its primary strength lies in identifying harmful "volatile organic compounds" (VOCs) that affect human health.

Key Features for Electrapac Customers

• Broad Spectrum Detection: Unlike specialized sensors (like the MQ-5 for methane), the MQ135 is a "generalist" that provides a comprehensive overview of air cleanliness.

• Dual Signal Output: * Analog Output (AO): Provides a continuous voltage (0V–5V) proportional to the concentration of pollutants—perfect for graphing air quality trends.

  • Digital Output (DO): Allows you to set a safety threshold using the onboard potentiometer to trigger an exhaust fan or an alarm.

• High Sensitivity: Capable of detecting trace amounts of hazardous gases long before they become noticeable to the human nose.

• Onboard Signal Conditioning: Features the LM393 comparator to ensure the digital switching signal is stable and free from electrical noise.

• Durable Design: The stainless steel mesh protects the sensing element from large dust particles while allowing air to flow freely for accurate sampling.

Wiring & Calibration Guide

The Electrapac MQ135 module is designed for easy integration with common microcontrollers:

1. VCC: Connect to 5V (The internal heater requires a constant 5V for chemical activation).

2. GND: Connect to common ground.

3. DO: Digital Output—goes LOW when the detected gas exceeds the set limit.

4. AO: Analog Output—voltage increases as the air quality decreases (higher ppm).

Pro-Tip: The "Preheat" Rule. To get accurate and stable readings, the MQ135 requires a 24-hour initial burn-in period. For daily use, allow the sensor to warm up for 2 to 5 minutes before recording data. If the sensor is used immediately after power-on, the readings will drift significantly.

Primary Applications

• Indoor Air Quality (IAQ) Monitors: Tracking "stuffiness" and pollutants in bedrooms, offices, or classrooms.

• Smart Ventilation Systems: Automatically turning on an air purifier or exhaust fan when CO_2 or smoke levels rise.

• Industrial Safety: Detecting ammonia or sulfide leaks in chemical processing plants.

• Environmental Data Logging: Using an ESP32 or Raspberry Pi to upload local pollution data to the cloud.

• Smart Toilets: Detecting high levels of ammonia to trigger automatic deodorizers or fans.

Why Shop at Electrapac?

We source the Genuine MQ135 Series with high-purity SnO2 sensing layers to ensure long-term stability and sensitivity. Visit us at www.electrapac.com for the sensing components that help you breathe easier.