Blink an LED on pin 9, on an Arduino Uno

// Blink an LED on pin 9.
//
//   pin 9 -> 220 ohm resistor -> the LED's long leg; the short leg -> GND
//
// digitalWrite(pin, HIGH) puts 5 V on the pin and the LED lights;
// digitalWrite(pin, LOW) takes it back to 0 V and the LED goes out. delay()
// waits a number of milliseconds in between. Change the 500s and run it again.

const int LED_PIN = 9;

void setup() {
  pinMode(LED_PIN, OUTPUT);
  Serial.begin(9600);
  Serial.println("Mokxi Uno: blinking the LED on pin 9");
}

void loop() {
  digitalWrite(LED_PIN, HIGH);
  delay(500);
  digitalWrite(LED_PIN, LOW);
  delay(500);
}