#define MQ9_PIN 12
#define BZ 27
#define LIMITE 50
#define NUMERO_TELEFONE "+5511999999999"
#define MENSAGEM_ALERTA "ATENÇÃO: Monóxido de carbono detectado! Risco de incêndio!"

const float MQ9_RL = 10.0;

void setup() {
  Serial.begin(115200);
  pinMode(BZ, OUTPUT);
}

void loop() {
  delay(10);

  int mq9Value = analogRead(MQ9_PIN);
  float mq9PPM = mq9Calibration(mq9Value);
  Serial.print("PPM CO: ");
  Serial.println(mq9PPM);
  delay(100);

  if(mq9PPM > LIMITE){
    Serial.println(MENSAGEM_ALERTA);
    tone(BZ, 1000, 100);
    delay(100);
    noTone(BZ);
    tone(BZ, 750, 100);
    delay(100);
    noTone(BZ);
  }
}

// Calcula PPM do sensor MQ9
float mq9Calibration(int rawValue) {
  float vrl = (float)rawValue * (3.3 / 4095.0);
  float rs = (5.0 - vrl) / vrl * MQ9_RL;
  float ppm = 91.8 * pow(10, 1.85 - (rs / 10)); // Calibration curve for MQ9
  return ppm;
}