HOW to Detect Alcohol With ESP32

Description

In this kit, there is a MQ-3 alcohol sensor, which uses the gas-sensing material is tin dioxide (SnO2) which has a low conductivity in clean air. When there is alcohol vapor in the environment where the sensor is located, the conductivity of the sensor increases with the increase of the alcohol gas concentration in the air. The change in conductivity can be converted into an output signal corresponding to the gas concentration using a simple circuit.

In the experiment, we read the analog value at the A0 end of the sensor and the digital value at the D0 end to judge the content of alcohol vapor in the air and whether they exceed the standard.

Working Principle

At a certain temperature, the conductivity changes with the composition of the ambient gas. When in use, A0 terminal reads the analog value corresponding to alcohol vapor; D0 terminal is connected to an LM393 chip (comparator), we can adjust and measure the alcohol vapor alarm threshold through the potentiometer, and output the digital value at D0. When the measured alcohol vapor content exceeds the critical point, the D0 terminal outputs a low level; when the measured alcohol vapor content does not exceed the critical point, the D0 terminal outputs a high level.

Components Required

Connection Diagram

Test Code

//**********************************************************************************
/*  
 * Description : Read the basic usage of Digital, ADC，DAC and Voltage
 * Auther      : http//www.keyestudio.com
*/
//MQ_3 two pins 13, 34, respectively 
#define PIN_ANALOG_IN  34
int digitalPin =  13;

//The following two variables hold the digital signal and adc values respectively
int analogVal = 0;
int adcVal = 0;

void setup() {
  Serial.begin(9600);
  pinMode(digitalPin, INPUT); //Digital pin 13 is set to input mode
}

//In loop()，the digitalRead()function is used to obtain the digital value,
//the analogRead() function is used to obtain the ADC value. 
//and then the map() function is used to convert the value into an 8-bit precision DAC value. 
//The input and output voltage are calculated according to the previous formula, 
//and the information is finally printed out.
void loop() {
  int digitalVal = digitalRead(digitalPin);  //Read digital signal;
  int adcVal = analogRead(PIN_ANALOG_IN);
  int dacVal = map(adcVal, 0, 4095, 0, 255);
  double voltage = adcVal / 4095.0 * 3.3;
  Serial.printf("digitalVal: %d, \t ADC Val: %d, \t DAC Val: %d, \t Voltage: %.2fV\n",digitalVal, adcVal, dacVal, voltage);
  if (digitalVal == 1) {
    Serial.println("  Normal");
  }
  else {
    Serial.println("  Exceeding");
  }
  delay(100); //Delay time 100 ms
}
//**********************************************************************************

Test Result

Connect the wires according to the experimental wiring diagram, compile and upload the code to the ESP32. After uploading successfully，we will use a USB cable to power on. Rotating the potentiometer on the sensor, we can adjust the yellow and green LED bright and not bright critical point. Open the monitor, set baud rate to 9600 and display the corresponding data and characters. When the sensor detects the alcohol gas, the yellow and green LED lights up and the digital value changes from 1 to 0, the ADC value, DAC value and voltage value decrease, as shown below.