int L1 = 7;
int L2 = 6;

void setup() {
  // put your setup code here, to run once:
  pinMode(L1, OUTPUT);
  pinMode(L2, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  digitalWrite(L1, HIGH);
  digitalWrite(L2, LOW);

  delay(500);

  digitalWrite(L1, LOW);
  digitalWrite(L2, HIGH);

  delay(500);

}