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

== Experimental System and Data Acquisition System ==

=== 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.

=== Alcohol Detection and Alarm System Using Arduino ===
==== System Overview ====
The system is designed to detect alcohol concentration in the surrounding air and provide both visual and audible warnings. It consists of several functional modules, each with a specific role.
The MQ-3 alcohol sensor is used as the sensing element. It detects alcohol vapor and outputs an analog voltage that varies depending on the concentration.
The Arduino Uno acts as the central controller. It reads the analog signal from the sensor, processes the data, and makes decisions based on a predefined threshold.
The LCD1602 display with I2C interface is used to present the measured value in real time. Compared to simpler indicators, the LCD provides a more flexible and readable output.
A red LED serves as a visual indicator. It is turned on when the detected alcohol level exceeds the safe limit.
A buzzer is used as an audible alarm. In this design, a transistor is included to drive the buzzer, ensuring that sufficient current can be supplied.
All modules are powered by the Arduino and share a common ground, forming a simple but complete sensing and alarm system.
==== Working Principle ====
The MQ-3 sensor operates based on changes in its internal resistance when exposed to alcohol vapor. As the alcohol concentration increases, the resistance of the sensing material decreases, resulting in a change in the output voltage.
This voltage is read by the Arduino through its analog-to-digital converter (ADC).
The ADC converts the analog signal into a digital value ranging from 0 to 1023.
In this project, the raw sensor value is scaled by dividing by 10 to obtain a simplified percentage-like value. Although this does not represent the exact alcohol concentration, it provides a convenient way to observe changes.
The system continuously monitors this value and compares it with a predefined threshold. When the measured value exceeds the threshold, the system enters an alarm state.
In the alarm state, the LED is turned on to provide a visual warning, and the buzzer is activated to produce an audible signal. When the value falls below the threshold, the system returns to the normal state.
==== Hardware Implementation ====
The MQ-3 sensor module is connected to the analog input pin (A0) of the Arduino. The module is powered by the 5V supply and shares a common ground.
The LCD1602 display uses I2C communication, which requires only two signal lines: SDA and SCL. This simplifies wiring and reduces the number of pins used on the Arduino.
The LED is connected to a digital output pin through a current limiting resistor to prevent excessive current.
The buzzer is controlled through a transistor. The Arduino provides a control signal to the transistor base, allowing the buzzer to be driven safely with sufficient current.
==== Software Design ====
The program is implemented using the Arduino IDE. Its main function is to read sensor data, display the result, and control the alarm outputs.
The analog signal from the MQ-3 sensor is read using the analogRead() function. The value is then scaled and displayed on the LCD.
At the same time, the system compares the value with a threshold (set to 30 in this project). Based on this comparison, the LED and buzzer are controlled.
A simplified version of the main logic is shown below:
int value = analogRead(A0) / 10;
lcd.setCursor(0, 0); lcd.print("alcohol:"); lcd.print(value); lcd.print("%");
if (value > 30) { digitalWrite(2, HIGH);	// LED ON digitalWrite(3, LOW);	// Buzzer state
} else { digitalWrite(2, LOW);	// LED OFF digitalWrite(3, HIGH);	// Buzzer state
}
The system updates once every second, allowing continuous monitoring of alcohol levels.