#define led_begin 1
#define led_end 12
boolean a = false;
int rita = led_begin;

void setup(){
  for (int i = led_begin; i <= led_end; i++)pinMode(i, OUTPUT);
  Serial.begin(9600);
}

void loop(){
  static unsigned long timer = 0;
  if (millis() - timer >= 100
    
  ) {
    timer = millis();
    digitalWrite(rita, a);
    rita++;
  }
  if (rita > led_end) {
    rita = led_begin;
    a = !a;
  }
  Serial.println(millis());
}