// Declare pin variable
int led_pin = 11;

void setup()
{
  // Setup code to run only once
  pinMode(led_pin, OUTPUT);
}

void loop()
{
  // Code to run repeatedly
  digitalWrite(led_pin, 1);
  delay(1000); // 1000ms -> 1s

  digitalWrite(led_pin, 0);
  delay(1000); // 1000ms -> 1s


}