int timer = 100;           // The higher the number, the slower the timing.
int ledPins[] = {  2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12};       // an array of pin numbers to which LEDs are attached
int pinCount = 11;           // the number of pins (i.e. the length of the array)


void setup()
{
  // use a for loop to initialize each pin as an output:
  for (int thisPin = 2; thisPin < 13; thisPin++)
  {
    pinMode(thisPin, OUTPUT);
  }
}

void loop()
{
  // Speed up over 25 cycles, delays of 100 to 50
  for (int timer = 120; timer > 20; timer -= 3)
  {
    oneCycle(timer);
  }
  // Slow down over 25 cycles, delays of 50 to 100
  for (int timer = 20; timer < 120; timer += 3)
  {
    oneCycle(timer);
  }
}






void oneCycle(int delayTime)
{
  // loop from the lowest pin to the highest:
  for (int thisPin = 2; thisPin < 13; thisPin++)
  {
    // turn the pin on:
    digitalWrite(thisPin, HIGH);
    delay(delayTime);
    // turn the pin off:
   // digitalWrite(thisPin, LOW);
  }
  // loop from the highest pin to the lowest:
  for (int thisPin = 12; thisPin >= 2; thisPin--)
  {
    // turn the pin on:
    //  digitalWrite(thisPin, HIGH);
    //  delay(delayTime);
    // turn the pin off:
    //digitalWrite(thisPin, LOW);
    digitalWrite(2, LOW);
    digitalWrite(3, LOW);
    digitalWrite(4, LOW);
    digitalWrite(5, LOW);
    digitalWrite(6, LOW);
    digitalWrite(7, LOW);
    digitalWrite(8, LOW);
    digitalWrite(9, LOW);
    digitalWrite(10, LOW);
    digitalWrite(11, LOW);
    digitalWrite(12, LOW);
  }
}