What is MQ3 Alcohol Sensor : Pin Configuration & Its Applications

The MQ3 alcohol sensor is one of the series of MQ gas sensors, which can detect and monitor the alcohol gas present in the atmosphere. It is capable of detecting 25-500ppm alcohol gas concentration in the air. This article gives a brief description of the pin configuration, specifications, and Arduino interfacing of the MQ3 alcohol sensor. The alternatives of MQ3 alcohol sensors are MQ138 (benzene, hydrogen, alcohol, propane, toluene, formaldehyde gas), MQ303A (ethanol, smoke, and alcohol), MQ2(methane, smoke, LPG, butane), MQ214 (methane), MQ5 (natural gas and LPG), and MQ306A (LPG and butane).

What is an MQ3 Alcohol Sensor?

The MQ3 alcohol gas sensor is a module used for detecting alcohol, CH4, benzene, gasoline, hexane, CO, and LPG. It has a sensitive material SnO2 for alcohol gas detection, with lower electrical conductivity in the fresh air. It is a semiconductor alcohol gas sensor that detects or monitors the presence or absence of alcohol. It is also known as chemiresistors because sensing of the sensitive material depends on the resistance change when the sensor is exposed to alcohol gas.

MQ3 Alcohol Sensor
MQ3 Alcohol Sensor

When the sensor is pointed closer to the alcohol gas, the SnO2 conductivity increases. The increase in sensor conductivity is directly proportional to the alcohol concentration. Therefore, the alcohol concentration is measured by any microcontroller very easily. The MQ3 alcohol gas sensor is very fast and has a high sensitivity to alcohol, smoke, and gasoline.  An Alcohol detector can be made using this alcohol sensor.

The concentration of alcohol gas sensing range in fresh air or atmosphere by the MQ3 sensor is 0.04mg/L-4 mg/L, which is acceptable for breathalyzers. It consumes 150 mA and operates with a 5V power supply at -10°C to 50°C temperature.

Pin Configuration and Structure:

The configuration and structure of the MQ3 alcohol sensor are shown in the figure below. It consists of 2 H-pins for supply and ground connection, 2 A-pins connected to the power supply, and 2 B-pins for output and ground connection. Since A-pins and B-pins can be interchanged.

MQ3 Sensor Configuration
MQ3 Sensor Configuration

Inside the MQ3 alcohol gas sensor, the resistance over A and B varies based on the alcohol detection. As the level of alcohol concentration detection increases, the resistance of the sensor decreases.


The MQ3 alcohol gas sensor consists of an AL2O3 micro-ceramic tube, a sensitive layer of tin dioxide (SnO2), a measuring electrode, and a heater attached to a grid made of stainless steel and plastic. The heater is necessary for providing the required conditions for the operation of sensitive components. The MQ-3 alcohol gas sensor has 6-pin, of which 4-pins are used to extract the signal and 2-pins are used to provide the heating current.

MQ3 Sensor Structure
MQ3 Sensor Structure

This alcohol sensor can generate an analogue output from the Ao pin (ranging from 0-5V) relating to the available alcohol gas concentration, otherwise use the built-in/onboard potentiometer to get a digital output (0 or 1) from the Do pin (Do LED is used to monitor the presence of alcohol gas concentration) for a specific gas concentration.

The manual calibration of the onboard potentiometer of the sensor is possible to change the digital output sensitivity and set the threshold value. If the concentration of alcohol vapor is above the threshold value (set by using an onboard potentiometer), then the output of the digital pin will be low. This is monitored easily when the Do LED glows. In addition, turning the potentiometer clockwise increases the sensitivity of the sensor.

MQ3 Alcohol Sensor Module Pin Out/Pin Diagram:

The MQ3 alcohol sensor comes in a 4-pin gas sensor module. The pin configuration/pin diagram is shown in the figure below.

Pin Configuration of MQ3 Module
Pin Configuration of MQ3 Module

VCC: This pin refers to the positive power supply. To power up the sensor, the 5V positive supply is connected to this pin

GND: This pin refers to the common ground connection.

Digital Output (Do): This pin generates the digital output signal by varying threshold limits with the help of an onboard potentiometer. This pin is to represent the digital output as 0 or 1 based on the alcohol gas present in the air.

Analog Output (Ao): This pin generates an analogue output signal in the range of 0V to 5V and it depends on the alcohol gas intensity.

MQ3 Alcohol Sensor Features:

Technical Specifications:

The MQ3 alcohol sensor technical specifications are listed below.

  • It requires a power supply of 5VDC (@ 165mA heater ON / 60mA heater off).
  • Consumes 150mA current.
  • Digital output Do: 0 and 1 TTL digital (0.1V and 5V).
  • Analog output Ao: 0.1V to 0.3V (relates to pollution), voltage concentration is maximum of 4V.
  • Alcohol Concentration detection: 0.05 mg/L to 10 mg/L.
  • Interface: one TTL compatible input (HSW) and one TTL compatible output (ALR).
  • Heater consumes: <750mW.
  • Resistance of the heater: 33ohms±5%.
  • Operating temperature: -10°C to 50°C (14°F to 122°F).
  • Storage temperature: 20°C to 70°C.
  • Load resistance is 200kilo ohms.
  • Sensitivity Rs: ≥5: Rs(in the air) / Rs(0.4mg/L Alcohol).
  • Sensing resistance Rs: 1Mega ohms to 8Mega ohms @ 0.4mg/L alcohol.
  • Sensor dimensions:32x22x16mm.
  • Humidity: <95%RH.
  • Oxygen concentration: 21%
  • Slope rate: ≤0.6.
  • Preheating duration: 20seconds.

Circuit Diagram of MQ3 Alcohol Sensor/How to Connect:

Now, let’s have a look at how to interface the MQ3 alcohol sensor with the Arduino UNO. In this case, the analogue output pin of the MQ3 sensor is used for proper sensor calibration. The circuit diagram/how to use the MQ3 alcohol sensor with the Arduino is shown in the figure below. The components required are;

Interfacing MQ3 with Arduino
              Interfacing MQ3 with Arduino
  • Arduino UNO.
  • MQ3 alcohol sensor.
  • 5V positive power supply.
  • Connecting wires.
  • Serial monitor to upload the Arduino code and observe the output.

Connect the MQ3 Sensor to Arduino UNO as per the above diagram.

The 5V operating voltage terminal of the Arduino is connected to the VCC pin of the MQ3 alcohol sensor. The analogue output pin of the sensor is connected to the Ao pin of the Arduino board. Note that, an analogue output pin is used and the digital output pin of the sensor is left. The GND pin of the MQ3 sensor is connected to the GND pin of the Arduino. Calibrate the sensor and set the threshold value by using an in-built potentiometer to detect and monitor alcohol concentration. Similar to the above way MQ3 Alcohol sensor can also be interfaced with the other microcontroller.

Upload the below Arduino code in Arduino IDE to observe the analogue output of the sensor.
To upload the Arduino code, select the Arduino board from the tools board and COM port, to which the Arduino is connected from the tools.

Arduino Code:

#define analog_pin 0 (Ao pin of Arduino connected to the analogue output pin of MQ3 sensor)
float sensor_value; (defines the sensor value to save the analogue output of the sensor)

void setup() {
Serial.begin(115200); (serial communication is set to 115200 baud rate)
Serial.println(“MQ3 is warming up”);
delay(120000); //2 min warm-up time (delay of 2 minutes to preheat the sensor for operation at required temperature)

void loop() {
sensor_value = analogRead(analog_pin); (analogue read is used on the analogue pin of the sensor to read and save the sensor value)
Serial.print(“Sensor Value: “);
delay(2000); (this process is repeated and the output is displayed on the serial monitor every 2 seconds)

Where to Use/Applications:

The applications of the MQ3 alcohol sensor are given below,

  • Used as a gas level over-limit alarm.
  • Portable alcohol detector.
  • Breathalyzer.
  • Stand-alone sensing module.
  • Used in environmental monitoring equipment.
  • Vehicle alcohol detector.

Please refer to this link for MQ3 Alcohol Sensor Datasheet.

Thus, this is all about an overview of the MQ3 alcohol gas sensor. It is used to detect/monitor different alcohol gas concentrations in the air. The different MQ series alcohol gas sensors are available in the market today. Choose the right one for the application.