// the setup function runs once when you press reset or power the board
void setup() 
{
    // initialize digital pin LED_BUILTIN as an output.
    pinMode(3, OUTPUT);
}

// the loop function runs over and over again forever
void loop() 
{
    digitalWrite(3, HIGH);   // turn the LED on (HIGH is the voltage level)
    delay(500);                       // wait for 1.5 second
    digitalWrite(3, LOW);    // turn the LED off by making the voltage LOW
    delay(3000);                       // wait for 0.5 second
}