Editing Alcohol Sensor Based on Gas-Sensitive Resistive Materials (section)

=== Experimental System Design ===

The experimental system was constructed using an Arduino Uno development board, an MQ-3 alcohol sensor module, an LCD1602 display with an I2C interface, a red LED indicator, and a 5 V buzzer. The MQ-3 sensor functioned as the sensing element, while the Arduino Uno performed signal acquisition and control. The LCD provided real-time display of sensor readings, and the LED together with the buzzer served as alarm outputs. The overall configuration of the experimental setup and the assembled prototype is presented in Figure 1.

[[File:Figure1.jpg|thumb|center|500px|Figure 1. Experimental setup and assembled hardware: (a) closed-chamber setup with laptop monitoring; (b) assembled hardware prototype.]]


To create a controllable test environment, the whole sensing system was placed inside a transparent plastic chamber during the measurements. Alcohol wipes were used as the ethanol source, and the source-to-sensor distance was adjusted to 0 cm, 5 cm, 10 cm, and 15 cm in separate tests. A laptop was connected to the Arduino through USB, and the Arduino Serial Plotter was used to observe the sensor output in real time. This configuration allowed the system response to be visualized continuously and made it possible to compare the signal evolution under different distance conditions.

Before each measurement, the sensor was powered on and allowed to warm up until the displayed baseline became relatively stable. In our experiments, the stabilized initial value was typically in the range of about 15 to 20. This procedure is necessary for MQ-3 operation because the sensing layer requires heating before stable output can be achieved.

According to the implemented circuit and program, the MQ-3 analog output was connected to pin A0, while the LCD communicated with the Arduino through the SDA and SCL lines. The alarm logic was implemented through digital output control, so that the system could provide both visual and audible warnings during alcohol exposure. The circuit schematic of the complete prototype is shown in Figure 2.

[[File:Figure2.png|thumb|center|500px|Figure 2. Circuit schematic of the prototype system, including the Arduino UNO, MQ-3 sensor, LCD1602 display, LED indicator, and buzzer.]]

The data acquisition method was designed for practical warning and trend observation rather than exact concentration metrology. The Arduino read the analog signal from pin A0, converted it through the Uno's 10-bit ADC, scaled the value by dividing by 10, and displayed it on the LCD as a percentage-like reading. The same value was also sent to the Serial Plotter once every second. A threshold of 30 was used in the control program: when the displayed value exceeded this threshold, the LED and buzzer were activated. Therefore, in this project the displayed number should be interpreted as a relative output used for over-limit judgment and response comparison, rather than as a calibrated ethanol concentration in physical units.