#define ledpin 2

void setup() {
  // initialize digital pin LED_BUILTIN as an output.
  pinMode(ledpin, OUTPUT);
}

void loop() {
  digitalWrite(ledpin, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(1000);                       // wait for a second
  digitalWrite(ledpin, LOW);    // turn the LED off by making the voltage LOW
  delay(1000);                       // wait for a second
}