void setup() {
  pinMode(16,OUTPUT);
  pinMode(17,OUTPUT);
  pinMode(18,OUTPUT);
  pinMode(19,OUTPUT);
}

void loop() {
  digitalWrite(16, 0);
  digitalWrite(17, 0);
  digitalWrite(18, 0);
  digitalWrite(19, 0);
  delay(1000);
  digitalWrite(16, 1);
  digitalWrite(17, 1);
  digitalWrite(18, 1);
  digitalWrite(19, 1);
  delay(1000);
}