Código Morse con Arduino

// Codigo Morse: emisor LED para Arduino UNO R3.
// A-Z, a-z, 0-9 y espacios. No requiere bibliotecas adicionales.
const byte LED_PIN = LED_BUILTIN;
const unsigned int DOT_MS = 120; // 10 WPM: 1200 / 10
const char MESSAGE[] = "SOS";

const char* const LETTERS[] = {
  ".-", "-...", "-.-.", "-..", ".", "..-.", "--.", "....", "..",
  ".---", "-.-", ".-..", "--", "-.", "---", ".--.", "--.-", ".-.",
  "...", "-", "..-", "...-", ".--", "-..-", "-.--", "--.."
};
const char* const DIGITS[] = {
  "-----", ".----", "..---", "...--", "....-",
  ".....", "-....", "--...", "---..", "----."
};

const char* codeFor(char character) {
  if (character >= 'a' && character <= 'z') character -= 'a' - 'A';
  if (character >= 'A' && character <= 'Z') return LETTERS[character - 'A'];
  if (character >= '0' && character <= '9') return DIGITS[character - '0'];
  return nullptr;
}

void sendLetter(const char* code) {
  for (unsigned int i = 0; code[i] != '\0'; ++i) {
    if (i > 0) delay(DOT_MS); // Pausa entre senales de una letra: 1 unidad.
    digitalWrite(LED_PIN, HIGH);
    delay(code[i] == '.' ? DOT_MS : 3UL * DOT_MS);
    digitalWrite(LED_PIN, LOW);
  }
}

bool sendMessage(const char* message) {
  // Valida todo antes de emitir: un caracter no admitido cancela el mensaje.
  bool hasCharacter = false;
  for (unsigned int i = 0; message[i] != '\0'; ++i) {
    if (message[i] == ' ') continue;
    if (codeFor(message[i]) == nullptr) return false;
    hasCharacter = true;
  }
  if (!hasCharacter) return false;

  bool sent = false;
  unsigned int gap = 0;
  for (unsigned int i = 0; message[i] != '\0'; ++i) {
    if (message[i] == ' ') {
      if (sent) gap = 7; // Pausa entre palabras: 7 unidades en total.
      continue;
    }
    if (sent) delay(static_cast<unsigned long>(gap) * DOT_MS);
    sendLetter(codeFor(message[i]));
    sent = true;
    gap = 3; // Pausa entre letras: 3 unidades en total.
  }
  return true; // No anade una pausa de letra al final.
}

void setup() {
  pinMode(LED_PIN, OUTPUT);
  digitalWrite(LED_PIN, LOW);
  Serial.begin(9600);
  delay(1000);
  if (!sendMessage(MESSAGE)) {
    Serial.println("Usa solo A-Z, 0-9 y espacios; sin tildes ni signos.");
  }
}

void loop() {
  // Una sola transmision. Pulsa RESET para repetir.
}