#include <Wire.h>
#include <hd44780.h>
#include <hd44780ioClass/hd44780_I2Cexp.h>

hd44780_I2Cexp lcd;

const int GAS_PIN   = A0;
const int GREEN_LED = 4;
const int RED_LED   = 5;
const int BUZZER    = 6;
const int RELAY_PIN = 7;

const int THRESHOLD = 300;   // set just below the value you reach when you raise the gas level

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

  pinMode(GREEN_LED, OUTPUT);
  pinMode(RED_LED, OUTPUT);
  pinMode(BUZZER, OUTPUT);
  pinMode(RELAY_PIN, OUTPUT);

  int status = lcd.begin(16, 2);
  if (status) {
    Serial.println("LCD not found - check SDA/SCL wiring");
  }

  lcd.print("SmokeGuard");
  lcd.setCursor(0, 1);
  lcd.print("Starting...");
  delay(1500);
  lcd.clear();
}

void loop() {
  int value = analogRead(GAS_PIN);
  Serial.println(value);

  lcd.setCursor(0, 0);

  if (value > THRESHOLD) {
    lcd.print("SMOKE DETECTED  ");
    lcd.setCursor(0, 1);
    lcd.print("Fan ON  Val:");
    lcd.print(value);
    lcd.print("   ");

    digitalWrite(GREEN_LED, LOW);
    digitalWrite(RED_LED, HIGH);
    tone(BUZZER, 1000);            // buzzer ON
    digitalWrite(RELAY_PIN, HIGH);
  } else {
    lcd.print("Air Normal      ");
    lcd.setCursor(0, 1);
    lcd.print("Fan OFF Val:");
    lcd.print(value);
    lcd.print("   ");

    digitalWrite(GREEN_LED, HIGH);
    digitalWrite(RED_LED, LOW);
    noTone(BUZZER);                // buzzer OFF
    digitalWrite(RELAY_PIN, LOW);
  }

  delay(300);
}