void loop()
{
  digitalWrite(D0, HIGH);
  delay(500);
  digitalWrite(D0, LOW);
  digitalWrite(D1, HIGH);
  delay(500);
  digitalWrite(D1, LOW);
  digitalWrite(D2, HIGH);
  delay(500);
  digitalWrite(D2, LOW);
  digitalWrite(D3, HIGH);
  delay(500);
  digitalWrite(D3, LOW);
  digitalWrite(D4, HIGH);
  delay(500);
  digitalWrite(D4, LOW);
  delay(500);
}