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

LiquidCrystal_I2C lcd(0x27, 16, 2);

const int MQ2_PIN = A0;   // Potentiometer = MQ2 sensor
const int FAN_PIN = 8;    // LED = Fan indicator
const int THRESHOLD = 500; // Above this = poor air

void setup() {
  lcd.init();
  lcd.backlight();
  pinMode(FAN_PIN, OUTPUT);
  lcd.setCursor(0, 0);
  lcd.print("Air Quality Sys");
  delay(2000);
  lcd.clear();
}

void loop() {
  int airValue = analogRead(MQ2_PIN);

  lcd.setCursor(0, 0);
  if (airValue > THRESHOLD) {
    digitalWrite(FAN_PIN, HIGH);   // Fan ON
    lcd.print("Air: POOR       ");
    lcd.setCursor(0, 1);
    lcd.print("Fan: ON         ");
  } else {
    digitalWrite(FAN_PIN, LOW);    // Fan OFF
    lcd.print("Air: GOOD       ");
    lcd.setCursor(0, 1);
    lcd.print("Fan: OFF        ");
  }

  delay(500);
}