Description
The MQ-135 Air Quality Sensor is a low-cost, highly sensitive gas detection module designed for monitoring air quality in indoor, industrial, and automotive environments. Built around the MQ-135 semiconductor sensor with a tin dioxide (SnO2) sensing layer, this module responds to a broad range of harmful gases including ammonia (NH3), sulfur compounds, benzene vapors, smoke, alcohol, and carbon dioxide equivalent (CO2eq). It is an ideal solution for home air quality monitors, gas leak alarms, smart ventilation systems, and educational sensor projects.
At the heart of the module is the MQ-135 sensor element, whose conductivity increases as the concentration of target gases rises. In clean air, the sensor exhibits low conductivity; when exposed to polluted air, its resistance drops, producing a measurable change in output. The module provides two independent outputs: an analog output (AO) that varies continuously with gas concentration for trend monitoring, and a digital output (DO) that switches when the concentration exceeds a user-adjustable threshold set by the onboard potentiometer. This dual-output design makes it suitable for both quantitative trend analysis and simple threshold-based alarm triggering.
The module operates from 5V DC with a typical current consumption of approximately 150mA. It is compatible with Arduino, ESP32, and other 5V microcontrollers; Raspberry Pi users require an external ADC. The board features four mounting holes for secure installation and a compact form factor. An onboard LED indicator provides visual feedback for power and digital output status.
Important Note: The MQ-135 requires a significant preheat time for stable operation. The sensor should be powered on for 24–48 hours in clean air before initial calibration for accurate readings. After each power-up, allow at least 20 seconds to 2 minutes for the heater to stabilize. The sensor is not a calibrated industrial-grade detector and should not be used as a primary life-safety device. Its sensitivity degrades over time, and periodic replacement is recommended for critical applications. The sensor surface becomes hot during operation — avoid touching it. The module is not waterproof and should be kept dry.
Whether you are building a home air quality monitor, a workshop safety alarm, or an educational sensor project, the MQ-135 module provides a reliable, affordable solution for broad-spectrum gas detection.
Features
-
MQ-135 SnO2 semiconductor sensor — High sensitivity to NH3, sulfur compounds, benzene, smoke, alcohol, and CO2 equivalent
-
Dual output — Analog (AO) for concentration trends, Digital (DO) for threshold alarms
-
Adjustable threshold — Onboard potentiometer sets the digital output trigger point
-
Wide detection range — 10–1000 ppm for target gases
-
5V operation — Compatible with Arduino, ESP32, and other 5V microcontrollers
-
LED indicators — Power and digital output status feedback
-
Four mounting holes — Secure installation in enclosures and project boxes
-
Compact form factor — 32 × 20 × 22mm PCB
-
Long lifespan — Specified for up to 10 years under proper operating conditions
-
Wide application range — Home air quality monitors, gas alarms, smart ventilation, education
Technical Specifications
| # | Parameter | Specification |
|---|---|---|
| 1 | Sensor Model | MQ-135 (SnO2 semiconductor) |
| 2 | Target Gases | NH3, sulfur compounds, benzene, smoke, alcohol, CO2 equivalent |
| 3 | Detection Range | 10 – 1000 ppm (target gases) |
| 4 | Operating Voltage | 5V DC |
| 5 | Operating Current | ~150mA |
| 6 | Output Type | Analog (AO) + Digital (DO/TTL) |
| 7 | Preheat Time | 24–48 hours (initial); ~20s–2min (each power-up) |
| 8 | PCB Dimensions | 32 × 20 × 22 mm |
Reviews
There are no reviews yet.