#define MQ2_PIN 2
#define BUZZER  12

int leds[5] = { 16, 17, 5, 18, 19 };
int gasValue = 0;

void setup() {
  Serial.begin(115200);

  for (int i = 0; i < 5; i++) {
    pinMode(leds[i], OUTPUT);
    digitalWrite(leds[i], LOW);
  }

  pinMode(BUZZER, OUTPUT);
  digitalWrite(BUZZER, LOW);

  analogReadResolution(12);                 // 0–4095
  analogSetPinAttenuation(MQ2_PIN, ADC_11db);

  Serial.println("🌫️ 5-Level Air Quality Monitoring Started");
}

void loop() {
  gasValue = analogRead(MQ2_PIN);
  Serial.print("Gas Value: ");
  Serial.println(gasValue);

  // Turn OFF all LEDs first
  for (int i = 0; i < 5; i++) {
    digitalWrite(leds[i], LOW);
  }
  digitalWrite(BUZZER, LOW);

  if (gasValue < 600) {
    digitalWrite(leds[0], HIGH);        // Very Clean
  } 
  else if (gasValue < 1200) {
    digitalWrite(leds[1], HIGH);        // Clean
  } 
  else if (gasValue < 1800) {
    digitalWrite(leds[2], HIGH);        // Moderate
  } 
  else if (gasValue < 2500) {
    digitalWrite(leds[3], HIGH);        // Unsafe
  } 
  else {
    digitalWrite(leds[4], HIGH);        // Dangerous
    digitalWrite(BUZZER, HIGH);         // Alarm ON
  }

  delay(1000);
}