char option = ' ';
int LED = 12;
void setup()
{
Serial.end();
Serial.begin(9600); 
pinMode(LED, OUTPUT);
delay(500);
Serial.println("************************************************");
Serial.println("*                  Menu                            *");
Serial.println("*              b = Apagar Led                         *");
Serial.println("*             a = Encender Led                     *");
Serial.println("*  Selecciona una opción, a=Encender b=apagar    *");
Serial.println("************************************************");
}

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