#define   RL 5  
#define   RAL 9.83                                             
#define   GAS_LP 0

float Calibracion(){
  int i;
  float val=0;
    for (i=0;i<50;i++) {                                                                               //tomar múltiples muestras
    val += calc_res(analogRead(27));
    delay(500);
  }
  val = val/50;                                                                                         //calcular el valor medio
  val = val/RAL;
  return val;
}

float calc_res(int pin)
{
  return ( ((float)RL*(4095-pin)/pin));
}

float lecturaMQ(int pin){
  int i;
  float rs=0;
  for (i=0;i<5;i++) {
    rs += calc_res(analogRead(pin));
    delay(50);
  }
rs = rs/5;
return rs;
}


void setup() {
  Serial.begin(115200);
  pinMode(27, INPUT);
  float Ro = Calibracion(); 
}

void loop() {
  Serial.print(lecturaMQ());
     delay(200);
}