Kwanzaa kinara on an Arduino Uno

// Kwanzaa kinara: seven candle lights, three red, one black and three green,
// with the day's principle on a little screen. Each press of the button is the
// next day of Kwanzaa, and one more candle is lit.
//
//   candles   7 WS2812B LEDs in a row, DIN <- 330 ohms <- pin 6
//             (left to right: red, red, red, black, green, green, green)
//   LCD       16x2 with an I2C backpack: SDA -> A4, SCL -> A5
//   button    pin 2 -> button -> GND        (INPUT_PULLUP): the next day
//
// Kwanzaa runs from December 26th to January 1st, a celebration of African
// American culture and heritage with a principle for each day, the Nguzo
// Saba. The kinara holds the mishumaa saba, the seven candles: the black one
// in the middle for the people, three red on the left for the struggle, and
// three green on the right for the future and hope.
//
// The black candle is lit first, on the first day. After that, one common
// order alternates from the outside in: the first red on the far left, then
// the first green on the far right, and so on toward the middle. Families
// differ a little in the order they use, so it is one line, ORDER, to change.
//
// Each candle's LED glows in its candle's color, red, warm white for the
// black candle, and green, with a flame's flicker on top.
//
// Things to try. Press the button for each day. Change ORDER to the one your
// family uses.

#include <Wire.h>
#include <LiquidCrystal_I2C.h>
#include <Adafruit_NeoPixel.h>

const int CANDLES = 7;
const int BUTTON_PIN = 2;

// Which place lights on each day: the black candle, then outside in.
const int ORDER[CANDLES] = {3, 0, 6, 1, 5, 2, 4};

const char *PRINCIPLES[CANDLES][2] = {
  {"Umoja", "Unity"},
  {"Kujichagulia", "Self-Determination"},
  {"Ujima", "Collective Work and Responsibility"},
  {"Ujamaa", "Cooperative Economics"},
  {"Nia", "Purpose"},
  {"Kuumba", "Creativity"},
  {"Imani", "Faith"},
};

Adafruit_NeoPixel kinara(CANDLES, 6, NEO_GRB + NEO_KHZ800);
LiquidCrystal_I2C lcd(0x27, 16, 2);

int day = 0;
bool lit[CANDLES];
const char *marquee = "";   // the bottom line, scrolled when it is long
int marqueeAt = 0;
unsigned long nextScroll = 0;

// Show the bottom line, sliding along one letter at a time if it is wider
// than the screen, with a pause at each end.
void scrollLine() {
  int len = strlen(marquee);
  if (len <= 16 || millis() < nextScroll) return;
  lcd.setCursor(0, 1);
  for (int i = 0; i < 16; i++) lcd.print(marquee[marqueeAt + i]);
  nextScroll = millis() + (marqueeAt == 0 || marqueeAt == len - 16 ? 1200 : 300);
  marqueeAt = marqueeAt >= len - 16 ? 0 : marqueeAt + 1;
}

// The candle's color at place i: red on the left, black (shown warm white)
// in the middle, green on the right, scaled by the flame's level.
void candle(int i, int v) {
  if (i < 3) kinara.setPixelColor(i, v, 0, 0);
  else if (i == 3) kinara.setPixelColor(i, v, v * 3 / 4, v / 3);
  else kinara.setPixelColor(i, 0, v, 0);
}

void setup() {
  Serial.begin(9600);
  pinMode(BUTTON_PIN, INPUT_PULLUP);
  kinara.begin();
  kinara.setBrightness(170);
  kinara.show();
  lcd.init();
  lcd.backlight();
  lcd.print("Habari Gani?");
  lcd.setCursor(0, 1);
  lcd.print("Press for day 1");
  Serial.println("Kwanzaa kinara: press the button for the first day");
}

void loop() {
  if (digitalRead(BUTTON_PIN) == LOW) {
    day++;
    if (day > CANDLES) {
      day = 0;
      for (int i = 0; i < CANDLES; i++) lit[i] = false;
      marquee = "";
      lcd.clear();
      lcd.print("Heri za Kwanzaa");
      Serial.println("Heri za Kwanzaa! All seven days are done");
    } else {
      lit[ORDER[day - 1]] = true;
      lcd.clear();
      lcd.print(PRINCIPLES[day - 1][0]);
      lcd.setCursor(0, 1);
      for (int i = 0; i < 16 && PRINCIPLES[day - 1][1][i]; i++) lcd.print(PRINCIPLES[day - 1][1][i]);
      marquee = PRINCIPLES[day - 1][1];
      marqueeAt = 0;
      nextScroll = millis() + 1200;
      Serial.print("Day ");
      Serial.print(day);
      Serial.print(": ");
      Serial.print(PRINCIPLES[day - 1][0]);
      Serial.print(", ");
      Serial.println(PRINCIPLES[day - 1][1]);
    }
    while (digitalRead(BUTTON_PIN) == LOW) delay(10);
  }

  for (int i = 0; i < CANDLES; i++) {
    if (lit[i]) candle(i, random(0, 15) == 0 ? random(120, 180) : random(200, 256));
    else kinara.setPixelColor(i, 0);
  }
  kinara.show();
  scrollLine();
  delay(50);
}