MQ135 Air Quality Gas Sensor Module

The MQ135 Air Quality Gas Sensor Module detects a range of harmful gases including ammonia (NH3), NOx, CO2, benzene, alcohol and smoke, making it a popular choice for air-quality monitoring and pollution-detection projects. Like other sensors in the MQ series, it provides both a digital output that trips when gas levels exceed a set threshold, and an analog output that gives a continuous reading proportional to gas concentration.

The module operates across a voltage range of 2.5V to 5.0V, typically run at 5V, and draws around 150mA. It requires a preheat period of roughly 30 seconds to a couple of minutes before readings settle, indicated by the onboard power LED. The onboard LM393 comparator IC and a 10k potentiometer let the sensor work independently of a microcontroller for simple threshold-based detection.

• Gas detection – Ammonia, NOx, CO2, alcohol, benzene and smoke
• Operating voltage – 2.5V to 5.0V, typically 5V
• Power consumption – Approximately 150mA
• Digital output – 0V to 5V TTL logic at 5V Vcc
• Analog output – 0V to 5V at 5V Vcc
• Comparator IC – Onboard LM393 with 10k sensitivity potentiometer
• Preheat time – 30 seconds to a few minutes
• Use case – Standalone gas detection or PPM measurement via microcontroller

For simple gas presence detection, the module can be used standalone with just the digital pin driving an LED or buzzer through a transistor. For calculating actual PPM values, the analog pin is read by a microcontroller and the Rs/Ro ratio is calculated against the sensor’s datasheet curve. The MQ135 Air Quality Gas Sensor Module is a reliable core component for air-quality monitors and smoke detectors.