void setup() {
  pinMode(16, OUTPUT);
  pinMode(17, OUTPUT);
  pinMode(4, OUTPUT);
  pinMode(2, OUTPUT);
  }

  void loop(){
    digitalWrite(16, HIGH);
    digitalWrite(17, HIGH);
    digitalWrite(4, HIGH);
    digitalWrite(2, HIGH);
    delay(500);

    digitalWrite(16, LOW);
    digitalWrite(17, LOW);
    digitalWrite(4, LOW);
    digitalWrite(2, LOW);
    delay(500);

    digitalWrite(16, HIGH);
    digitalWrite(17, HIGH);
    digitalWrite(4, LOW);
    digitalWrite(2, LOW);
    delay(500);

    digitalWrite(16, LOW);
    digitalWrite(17, LOW);
    digitalWrite(4, HIGH);
    digitalWrite(2, HIGH);
    delay(500);

    digitalWrite(16, HIGH);
    digitalWrite(17, HIGH);
    digitalWrite(4, HIGH);
    digitalWrite(2, HIGH);
    delay(500);;

    digitalWrite(16, LOW);
    digitalWrite(17, LOW);
    digitalWrite(4, HIGH);
    digitalWrite(2, HIGH);
    delay(500);
  }
  //คำสั่งชุดนี้ควบคุมไฟทั้ง4ดวงให้ติดและดับเป็นแบบสลับกัน โดยเปลี่ยนรูปแบบทุกๆ0.5วินาที วนลูปอย่างต่อเนื่อง