#define led 13
char letra = "x";

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  pinMode(led, OUTPUT);
  Serial.println("Hello Arduino\n");
}

void loop() {
  // put your main code here, to run repeatedly:
  if (Serial.available() > 0) {
    letra = Serial.read();
    Serial.println(letra);
  }
  if (letra == "A") {
    digitalWrite(led, HIGH);

  }
}