#include <Adafruit_NeoPixel.h>

#define PIN        9
#define NUMPIXELS 12

Adafruit_NeoPixel pixels(NUMPIXELS, PIN, NEO_GRB + NEO_KHZ800);

const uint32_t RED = pixels.Color(225, 0, 0);
const uint32_t COLOUR = RED;

const int MIN_BRIGHTNESS = 140;
const int MAX_BRIGHTNESS = 200;
const int BRIGHTNESS_STEP = 1;
const int CHANGE_DELAY = 100;

int currentBrightness = MIN_BRIGHTNESS;
int direction = 1;

void setup() {
  // put your setup code here, to run once:
  pixels.begin();
}

void setAllPixels(int brightness) {
  pixels.fill(COLOUR, 0, pixels.numPixels());
  pixels.setBrightness(brightness);
  pixels.show();
}

void setDirectionBrighter() {
  direction = 1;
}
void setDirectionDarker() {
  direction = -1;
}

void loop() {
  setAllPixels(currentBrightness);

  if (currentBrightness > MAX_BRIGHTNESS) {
    setDirectionDarker();
  }

  if (currentBrightness < MIN_BRIGHTNESS) {
    setDirectionBrighter();
  }

  currentBrightness = currentBrightness + (BRIGHTNESS_STEP * direction);
  delay(CHANGE_DELAY);
}