MQ-135 Air Quality Sensor Detection Module

The MQ-135 Air Quality Sensor detection module senses harmful gases in the air, including ammonia (NH3), nitrogen oxides (NOx), benzene, alcohol, smoke and CO2. The sensing element changes its resistance as the gas level changes, and the module turns this into an analog voltage plus a digital output that switches at a threshold you set with the on-board potentiometer. It is a popular choice for Arduino and ESP32 air quality monitors and ventilation projects.

MQ-135 Air Quality Sensor Specifications

• Sensor: MQ-135 metal-oxide (tin dioxide) gas sensor
• Detects: NH3, NOx, alcohol, benzene, smoke and CO2
• Detection range (datasheet): 10–300 ppm NH3, 10–1000 ppm benzene, 10–300 ppm alcohol
• Supply voltage: 5 V (heater 5 V ± 0.1 V)
• Heater power: less than 800 mW
• Outputs: AO (analog voltage) and DO (digital, threshold set with the potentiometer)
• Pins: VCC, GND, DO, AO

MQ-135 Air Quality Sensor Applications

• Indoor air quality monitors with Arduino or ESP32
• Switching on a fan or ventilation when the air gets worse
• Detecting ammonia or solvent fumes in workshops and storage rooms
• Smart home and IoT data logging projects
• Sensor experiments in schools and universities

What's in the Box

• 1 × MQ-135 air quality sensor module

Tip: The heater runs warm and needs time to settle: let the sensor run for a few minutes before taking readings, and run a new sensor for 24 hours or more before calibrating, as the datasheet advises. The module is good at showing changes in air quality, but it is not a calibrated CO2 meter.

Orders placed before 14:00 are ready for pickup the same day. Delivery across Lebanon usually takes 1–3 working days.