void setup()
{
// initialize digital pin LED_BUILTIN as an output.
pinMode(LED_BUILTIN, OUTPUT);
}
// the loop function runs over and over again forever
void loop()
{
digitalWrite(LED_BUILTIN, HIGH);//turn the LED on
delay(1000); // wait for a second (1 sec = 1000ms)
digitalWrite(LED_BUILTIN, LOW); // turn the LED off by making the voltage LOW
delay(2000); // wait for a second (2 sec = 2000ms)
}