MQ-3 Alcohol / Ethanol Gas Sensor

🔹 MQ-3 – Alcohol / Ethanol Gas Sensor (Semiconductor Type)

A semiconductor-based gas sensor designed to detect the presence of alcohol, ethanol, and benzene vapors in the air. It is highly sensitive to alcohol and commonly used in breathalyzer prototypes, alcohol detection systems, and air quality monitors. The sensor requires a simple heater circuit and outputs an analog resistance that changes with gas concentration.

✅ Specifications:

• Sensor Type: Metal Oxide Semiconductor (MOS)

• Target Gases: Alcohol (Ethanol C2H5OH), Benzene, CH4, CO, LPG (Primary sensitivity: Alcohol)

• Detection Range: 10 – 1000 ppm (parts per million) of alcohol

• Heater Voltage: 5.0V ± 0.1V AC or DC (Critical for stable operation)

• Circuit Voltage (Vc): Up to 24V DC (Typically 5V for microcontroller interfacing)

• Load Resistance (RL): Adjustable, typically 10kΩ – 47kΩ

• Heater Resistance (RH): ~33Ω ± 5Ω (Cold)

• Heater Power Consumption: ~750mW

• Sensor Resistance (Rs): 2kΩ – 20kΩ in clean air (varies by specific sensor)

• Preheat Time: At least 24-48 hours for initial stabilization. Warm-up time: ~5-10 minutes for reliable readings after power-on.

• Output Signal: Analog Resistance (converted to voltage via a simple voltage divider circuit).

• Module Features: Common breakout boards include a comparator (LM393) for digital output with adjustable threshold, and a power indicator LED.

• Operating Temperature: -10°C to +50°C

• Operating Humidity: < 95% RH

⚙️ Key Features:

• High Sensitivity to Alcohol: Particularly responsive to ethanol vapors, making it ideal for breathalyzer projects.

• Wide Detection Range: Can detect from low to high concentrations.

• Analog & Digital Output: Raw analog reading for concentration estimation and a digital trigger for simple alarm systems.

• Simple Drive Circuit: Requires only a stable 5V heater supply and a load resistor to operate.

• Low Cost: The most accessible sensor for alcohol detection experiments.

📦 Typical Applications:

• Breathalyzer Prototypes: DIY alcohol detection devices (for educational purposes).

• Alcohol Detection in Vehicles: Safety systems to prevent drunk driving (conceptual projects).

• Air Quality Monitoring: Detecting alcohol or solvent vapors in industrial or laboratory environments.

• Fermentation Process Monitoring: In winemaking or biofuel production.

• Educational Demonstrations: Learning about gas sensors and environmental sensing.

🔧 Wiring & Basic Usage (Arduino with Analog Output):

1. Connections to a Breakout Module:

   • VCC → Arduino 5V

   • GND → Arduino GND

   • A0 (Analog Out) → Arduino Analog Pin (e.g., A0)

   • D0 (Digital Out) → Arduino Digital Pin (e.g., D2) – Optional, for threshold alarm

2. Operation: The sensor’s resistance (Rs) decreases in the presence of alcohol. In a voltage divider with a load resistor (RL), this causes the output voltage (Vout) to increase.

3. Basic Code (Analog Read):
   cpp

   int sensorPin = A0;
   void setup() {
   Serial.begin(9600);
   }
   void loop() {
   int sensorValue = analogRead(sensorPin);
   Serial.print(“Sensor Value: “);
   Serial.println(sensorValue);
   delay(1000);
   }

4. Calibration: Requires exposure to known concentrations of alcohol in a controlled environment. For most hobbyist projects, relative changes (e.g., baseline vs. detected) are sufficient.

⚠️ Critical Limitations & Usage Notes:

• Long Preheat & Burn-in: Requires an initial “burn-in” of 24-48 hours of continuous power for the readings to stabilize. Before each use, it needs 5-10 minutes to warm up.

• Non-Selective: Responds to many volatile organic compounds (VOCs) like alcohol, benzene, CO, and cigarette smoke. Not specific to alcohol alone. False positives are common.

• Environmental Sensitivity: Readings are highly affected by temperature and humidity. For consistent results, use in a controlled environment or implement compensation.

• Heater Voltage is Critical: The 5V heater supply must be clean and stable. Noise or fluctuation will cause erratic readings.

• Not for Safety-Critical Applications: This is a qualitative or semi-quantitative sensor for experimentation. Do not rely on it for life-saving or legal applications.

• Sensor Aging: Sensitivity degrades over time (typically 1-2 years of continuous use).