• EMULATOR: https://wokwi.com/projects/398033818496484353

int LED_RED = 4;

void setup() {
  pinMode(LED_RED, OUTPUT);
}

void loop() {
   digitalWrite(LED_RED, HIGH); // switch on PIN
   delay(500);                  // wait 0.5 seconds
   digitalWrite(LED_RED, LOW);  // switch off PIN
   delay(500);                  // wait 0.5 seconds

}