void setup() {
  // put your setup code here, to run once:
  pinMode(23, OUTPUT);
 pinMode(21,OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  digitalWrite(23,1);
  delay(500);
  digitalWrite(23,0);
  delay(500);
  digitalWrite(23,1);
  delay(500);
  digitalWrite(23,0);
  delay(500);

}