char option = "";
int LED = 12;

void setup() {
  Serial.end();
  delay(500);
  Serial.begin(9600);
  pinMode(LED, OUTPUT);
  delay(500);
  Serial.println();
  Serial.println();
  Serial.println("**********************");
  Serial.println("* Menu              *");
  Serial.println("*                   *");
  Serial.println("*  a = Apagar Led   *");
  Serial.println("*  b = Encender Led *");
  Serial.println("*                   *");
  Serial.println("* Selecciona una opción, a=apagar b=Encender *");
  Serial.println("**********************");
  Serial.println();
}

void loop() {
  if (Serial.available() > 0) {
    option = Serial.read();
    if (option == 'a') {
      digitalWrite(LED, LOW);
    } 
    else if (option == 'b') {
      digitalWrite(LED, HIGH);
    }
  }
  delay(100);
}