void setup() {
  // put your setup code here, to run once:
 pinMode(11, OUTPUT);
 pinMode(12, OUTPUT);
}


void loop() {
  // put your main code here, to run repeatedly:
  digitalWrite(11,1);
   digitalWrite(12,0);
   delay(500);
   digitalWrite(11,0);
   digitalWrite(12,1);
   delay(500);
}