Blink2

#define LED_BUILTIN 2						
							
// the setup function runs once when you press reset or power the board							
void setup() {							
  // initialize digital pin LED_BUILTIN as an output.							
  pinMode(LED_BUILTIN, OUTPUT);							
  Serial.begin(115200);							
}							
							
// the loop function runs over and over again forever							
void loop() {							
  Serial.printf("LED %d: HIGH\n", LED_BUILTIN);							
  digitalWrite(LED_BUILTIN, HIGH);   // turn the LED on (HIGH is the voltage level)							
  delay(1000);                       // wait for a second							
  Serial.printf("LED %d: LOW\n", LED_BUILTIN);							
  digitalWrite(LED_BUILTIN, LOW);    // turn the LED off by making the voltage LOW							
  delay(1000);                       // wait for a second							
}							

Variante

#define BLED 2//onboard BlueLED

void setup()
{
  Serial.begin(115200);
  pinMode(BLED, OUTPUT);
}

void loop()
{
  digitalWrite(BLED, HIGH);
  delay(1000);
  digitalWrite(BLED, LOW);
  delay(1000);
}