5.4.16 Project 8.2 Dangerous Gas Alarm

1. Description

When a gas sensor detects a high concentration of dangerous gas, the buzzer will sound an alarm and the display will show dangerous.

2. Component Knowledge

MQ2 Smoke Sensor: It is a gas leak monitoring device for homes and factories, which is suitable for liquefied gas, benzene, alkyl, alcohol, hydrogen as well as smoke detection. Our sensor leads to digital pin D and analog output pin A, which is connected to D as a digital sensor in this project.

3. Test Code

#include <Wire.h>
#include <LiquidCrystal_I2C.h>

// Initialize LCD with I2C address 0x27, 16 columns and 2 rows
LiquidCrystal_I2C mylcd(0x27, 16, 2);

#define gasPin 23    // Gas sensor input pin
#define buzPin 25    // Buzzer output pin

// State flags for LCD display updates
boolean dangerDisplayed = 1;
boolean safetyDisplayed = 1;

void setup() {
  Serial.begin(9600);

  // Initialize LCD
  mylcd.init();
  mylcd.backlight();

  // Set pin modes
  pinMode(buzPin, OUTPUT);
  pinMode(gasPin, INPUT);

  // Display initial message
  mylcd.setCursor(0, 0);
  mylcd.print("safety");
}

void loop() {
  boolean gasVal = digitalRead(gasPin);  // Read gas sensor value
  Serial.println(gasVal);

  if(gasVal == 0)  // If dangerous gas detected
  {
    while(dangerDisplayed == 1)  // Update display if needed
    {
      mylcd.clear();
      mylcd.setCursor(0, 0);
      mylcd.print("dangerous");
      dangerDisplayed = 0;
      safetyDisplayed = 1;
    }

    // Sound alarm buzzer (short pulses)
    digitalWrite(buzPin, HIGH);
    delay(1);
    digitalWrite(buzPin, LOW);
    delay(1);
  }
  else  // No dangerous gas detected
  {
    digitalWrite(buzPin, LOW);  // Ensure buzzer is off

    while(safetyDisplayed == 1)  // Update display if needed
    {
      mylcd.clear();
      mylcd.setCursor(0, 0);
      mylcd.print("safety");
      dangerDisplayed = 1;
      safetyDisplayed = 0;
    }
  }
}

4. Test Result

The screen displays “safety” in normal state. However, when the gas sensor detects some dangerous gases, such as carbon monoxide, at a certain concentration, the buzzer will sound an alarm and the screen displays “dangerous”.