Red envelope box on an Arduino Uno

// Red envelope reveal box: a little box for a red envelope. Press the button
// and the lid swings open, a light comes on inside and the display shows a
// good wish for the new year.
//
//   button    pin 2 -> button -> GND        (INPUT_PULLUP, pressed reads LOW)
//   servo     PWM -> pin 9, VCC -> 5 V, GND -> GND (the lid)
//   lamp      pin 5 -> 220 ohms -> yellow LED -> GND
//   LCD       16x2 with an I2C backpack: SDA -> A4, SCL -> A5
//
// Red envelopes (hongbao in Mandarin, lai see in Cantonese, li xi in
// Vietnamese) are given at Lunar New Year with money inside and good wishes
// outside. Put one in the box, and the wish on the screen is the card.
//
// The wishes are in a list and one is picked at random each time. A random
// pick can repeat, so the sketch remembers the last one and moves on if it
// comes up again.
//
// Things to try. Press the button. Write your own wishes into WISHES, two
// lines of up to 16 letters each. Make the lid stay open longer with OPEN_MS.

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

const int BUTTON_PIN = 2;
const int LAMP_PIN = 5;
const int SERVO_PIN = 9;
const int SHUT = 10, OPEN = 110;
const unsigned long OPEN_MS = 6000;

LiquidCrystal_I2C lcd(0x27, 16, 2);
Servo lid;

const char *WISHES[][2] = {
  {"Happy Lunar", "New Year!"},
  {"Xin nian", "kuai le!"},
  {"Wishing you", "good health"},
  {"Peace and joy", "all year long"},
  {"May your year", "be bright"},
  {"Lots of luck", "and laughter"},
};
const int COUNT = sizeof(WISHES) / sizeof(WISHES[0]);

int last = -1;
int opened = 0;

void idle() {
  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print("A red envelope");
  lcd.setCursor(0, 1);
  lcd.print("for you: press");
}

void swing(int from, int to) {
  int step = from < to ? 5 : -5;
  for (int a = from; a != to + step; a += step) {
    lid.write(a);
    analogWrite(LAMP_PIN, map(a, SHUT, OPEN, 0, 255));
    delay(25);
  }
}

void setup() {
  Serial.begin(9600);
  pinMode(BUTTON_PIN, INPUT_PULLUP);
  pinMode(LAMP_PIN, OUTPUT);
  lid.attach(SERVO_PIN);
  lid.write(SHUT);
  lcd.init();
  lcd.backlight();
  randomSeed(analogRead(A0));
  idle();
  Serial.println("Red envelope box ready");
}

void loop() {
  if (digitalRead(BUTTON_PIN) == HIGH) return;

  int pick = random(0, COUNT);
  if (pick == last) pick = (pick + 1) % COUNT;
  last = pick;
  opened++;

  // Open slowly, so the envelope is revealed rather than thrown.
  swing(SHUT, OPEN);
  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print(WISHES[pick][0]);
  lcd.setCursor(0, 1);
  lcd.print(WISHES[pick][1]);
  Serial.print("Opened ");
  Serial.print(opened);
  Serial.print(": ");
  Serial.print(WISHES[pick][0]);
  Serial.print(" ");
  Serial.println(WISHES[pick][1]);

  delay(OPEN_MS);
  swing(OPEN, SHUT);
  digitalWrite(LAMP_PIN, LOW);
  idle();
  Serial.println("Lid shut");
  while (digitalRead(BUTTON_PIN) == LOW) delay(10);
}