The MQ-3 gas sensor board is a semiconductorbased sensor module specifically optimized for the detection of ethanol vapors, making it suitable for alcohol concentration measurement applications such as breath alcohol testers. The sensing element exhibits high sensitivity to alcohol while also responding to hydrogen, which should be considered during application design and calibration. The typical detection range spans from 100 to 10,000 ppm.

The module operates from a 5 V DC supply and integrates the required heater circuitry to maintain the sensing element at its specified operating temperature. Gas concentration changes are reflected by variations in the sensor resistance, which are converted into an analog voltage output ranging from 0 to 5 V. In addition, the board provides a digital output generated by an onboard comparator with an adjustable threshold, allowing direct use in switching or alarm applications.

After each power-up, the sensor requires a heatup time of approximately 10 to 15 minutes before reliable measurements can be obtained. For initial commissioning, a burn-in period of 48 to 168 hours of continuous operation is recommended to stabilize the sensing element. Following this period, a baseline resistance measurement in clean air should be recorded as a reference value. If the sensor has been powered off for several weeks or longer, repeating the burn-in and baseline procedure is advised to maintain measurement consistency.

The board is equipped with power and status LEDs for visual indication of operation and detection status. For mechanical and layout flexibility, the LEDs may alternatively be soldered on the opposite side of the PCB. Electrical interfacing is provided via a 4-pin 2.54 mm header and a Molex PicoBlade connector, enabling straightforward integration into embedded systems, microcontroller platforms, and gas detection devices.