bool DEBUG = 0;

#include <Adafruit_NeoPixel.h> // https://github.com/adafruit/Adafruit_NeoPixel
#define PIN  4 // NeoPixel pin
#define PIX 40 // Number of NeoPixels 5 x 8)
Adafruit_NeoPixel WS2812 = Adafruit_NeoPixel(PIX, PIN, NEO_GRB + NEO_KHZ800);

unsigned long timer, timeout = 5; // milliseconds
bool direction; // for color change of direction

int value, mini = 51, maxi = 255; // color values

void setup() {
  if (DEBUG)
    Serial.begin(115200); // initialize serial communications
  WS2812.begin(); // initialize Neopixel object/instance
  WS2812.clear(); // clear display buffer
  WS2812.show();  // display pixel buffer
}

void loop() {
  int color, pixel;
  direction = !direction;

  for (color = 0; color < maxi - mini; color++) {
    for (pixel = 0; pixel < PIX; pixel++) {
      if (direction)
        value = mini + color;
      else
        value = maxi - color;
      WS2812.setPixelColor(pixel, WS2812.Color(value, value, value));
    }
    WS2812.show();  // display pixel buffer
    if (DEBUG) {
      Serial.print(direction);
      Serial.print(" ");
      Serial.println(value);
    }
  }
  delay(100);
}