int leds[] = {6, 7, 8, 9, 10, 11, 12, 13};
byte pinCount = 8;
int vardelay = 100;

void setup() {
  Serial.begin(115200);
  for(int i = 0; i < pinCount; i++) {
    pinMode(leds[i], OUTPUT);
  }
  Serial.println("ready..");
}

void loop() {
  for(int i = 0; i < pinCount; i++) {
    digitalWrite(leds[i], LOW);
    delay(vardelay);
  }
  for(int i = pinCount; i >= 0; i--) {
    digitalWrite(leds[i], HIGH);
    delay(vardelay);

  }

}