Attributes

Brand	-
Category	Robotics / STEM Teaching Tools / Sensors
Origin	-
Model Number	MQ-135
Detection Gases	NH3, NOx, Alcohol, Benzene, Smoke, CO2
Operating Voltage	5V DC
Output Signal	Analog and Digital (TTL)
Preheat Time	24-48 Hours
Load Resistance	20kΩ (Adjustable)
Heater Resistance	33Ω ±5%
Heater Current	-
Interface Type	3-Pin Header (VCC, GND, OUT)
Compatibility	Arduino, Raspberry Pi, ESP32, STM32

6 reviews

Anonymous

Mar 26, 2026

Rating: 3/5

Works well but needs calibration

The sensor is functional out of the box, but for accurate ppm estimates, you definitely need to calibrate it against known clean air conditions. For simple presence detection of bad air, it works perfectly without extra steps.

Anonymous

Mar 19, 2026

Rating: 5/5

Perfect for my home air monitor project

This sensor works exactly as described. I connected it to an Arduino Uno and had readings within minutes after the initial burn-in period. The analog output is stable and responds well to changes in air quality when testing with safe household items like alcohol wipes.

Anonymous

Mar 16, 2026

Rating: 5/5

Essential for ventilation control

I use this to trigger a fan in my workshop when VOC levels get too high. The digital threshold potentiometer on the board makes it easy to set the trigger point without writing complex code. Highly recommended for DIY automation.

Anonymous

Mar 13, 2026

Rating: 5/5

Reliable detection module

Bought two of these for a dual-sensor setup. Both performed consistently. I appreciate that it detects a broad range of harmful gases, making it versatile for general air quality monitoring rather than just one specific gas.

Anonymous

Mar 11, 2026

Rating: 4/5

Good value but requires patience

Great little module for the price. Just remember that you need to let it preheat for at least 24 hours before taking serious measurements, or the readings will drift. Once stabilized, it detects smoke and fumes very reliably.

Anonymous

Mar 01, 2026

Rating: 4/5

Solid performance for hobbyists

The build quality is decent for a budget sensor. It gets quite hot during operation, which is normal for this type of semiconductor sensor. Make sure your power supply can handle the current draw during the heating phase.

5 FAQ

Q: Can this detect carbon monoxide specifically?

A: The MQ-135 is sensitive to Carbon Monoxide (CO), but it is a broad-spectrum sensor. It reacts to many gases including NH3, NOx, and alcohol. For critical life-safety CO detection, we recommend a dedicated electrochemical CO sensor.

Q: What is the difference between the DO and AO pins?

A: AO (Analog Output) provides a continuous voltage proportional to the gas concentration. DO (Digital Output) goes HIGH or LOW based on a threshold you set using the small blue potentiometer on the board.

Q: How long does the preheating take?

A: For stable and accurate readings, we recommend a preheating time of 24 to 48 hours. Shorter periods may result in drifting baseline values, though the sensor will still respond to strong gas presence immediately.

Q: Does this sensor come with a library for Arduino?

A: The module itself is hardware only and does not include software. However, there are many open-source libraries available on GitHub and the Arduino Library Manager that support the MQ-135 specifically.

Q: Why is the sensor getting very hot?

A: This is normal operation. The MQ-135 contains an internal heating element required to maintain the metal oxide semiconductor at the correct operating temperature for gas detection. Ensure it has adequate airflow.

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