char option = ' ';
int LED = 12;
void setup() {
   Serial.begin(9600);
  pinMode(LED, OUTPUT);
}
void loop() {
  if (Serial.available() != 0){
    option = Serial.read();
    if (option == 'a'){
      digitalWrite(LED, HIGH);
    }
    else if(option == 'b'){
      digitalWrite(LED, LOW);
    }
    Serial.println("opcion");
    Serial.println(option);
  }
  
  delay(100);
}