#include <Adafruit_NeoPixel.h>

#define NUM_LEDS 70
#define PIN 6

Adafruit_NeoPixel strip = Adafruit_NeoPixel(NUM_LEDS, PIN, NEO_GRB + NEO_KHZ800);

void setup() {
  strip.begin();
  strip.setBrightness(50);
  strip.show(); // Initialize all pixels to 'off'
}

void loop() {
  animate(20);
}


// Slightly different, this makes the rainbow equally distributed throughout
void animate(uint8_t wait) {
  static uint16_t start = 0;
  strip.fill(0, 0,NUM_LEDS/2); // erase the first half
  // fill up that half  strip
  for (int32_t i = NUM_LEDS / 2-start; i >=0; i--) {
    strip.setPixelColor(i, 0xFF0000); // red
  }
  // now mirror
  for (int32_t i = NUM_LEDS - 1; i >= NUM_LEDS / 2; i--) {
    strip.setPixelColor(i, strip.getPixelColor(NUM_LEDS - 1 - i));
  }
  if (++start >= NUM_LEDS / 2) start = 0;
  strip.show();
  delay(wait);
}