Message display gift on an Arduino Uno

// Message display gift: a little screen for Mother's Day, Father's Day or a
// birthday, full of notes you wrote yourself. Press the button for the next
// one, and a heart glows on every new message.
//
//   LCD       16x2 with an I2C backpack: SDA -> A4, SCL -> A5
//   button    pin 2 -> button -> GND        (INPUT_PULLUP)
//   heart     pin 5 -> 220 ohms -> red LED -> GND
//
// The whole gift is the list in MESSAGES: two lines of up to 16 letters each.
// Write as many as you like, for a mom, a dad, a grandparent, a stepparent or
// anyone who looks after you, with their name in it. The first message
// shows at power-up, and after the last one it starts again.
//
// The heart on the LCD is a custom character, eight rows of five dots. When
// nobody has pressed the button for a while, the screen moves on by itself,
// so the gift keeps talking on a shelf.
//
// Things to try. Press the button. Write your own MESSAGES, with a name.
// Set AUTO_MS to 0 to make it wait for the button.

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

const int BUTTON_PIN = 2;
const int HEART_PIN = 5;
const unsigned long AUTO_MS = 20000UL;

LiquidCrystal_I2C lcd(0x27, 16, 2);

const uint8_t HEART[8] = {0b00000, 0b01010, 0b11111, 0b11111, 0b01110, 0b00100, 0b00000, 0b00000};

const char *MESSAGES[][2] = {
  {"Happy Mother's", "Day!"},
  {"Thank you for", "everything"},
  {"You make every", "day better"},
  {"Best hugs in", "the world"},
  {"I love you", "to the moon"},
  {"Love always,", "for you, Mom"},
};
const int COUNT = sizeof(MESSAGES) / sizeof(MESSAGES[0]);

int shown = 0;
unsigned long shownAt = 0;

void show(int n) {
  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print(MESSAGES[n][0]);
  lcd.setCursor(0, 1);
  lcd.print(MESSAGES[n][1]);
  lcd.setCursor(15, 1);
  lcd.write(0);
  shownAt = millis();
  Serial.print("Message ");
  Serial.print(n + 1);
  Serial.print(": ");
  Serial.print(MESSAGES[n][0]);
  Serial.print(" ");
  Serial.println(MESSAGES[n][1]);
  // The heart glows up and fades.
  for (int v = 0; v < 256; v += 8) {
    analogWrite(HEART_PIN, v);
    delay(8);
  }
  for (int v = 255; v >= 0; v -= 4) {
    analogWrite(HEART_PIN, v);
    delay(8);
  }
}

void setup() {
  Serial.begin(9600);
  pinMode(BUTTON_PIN, INPUT_PULLUP);
  pinMode(HEART_PIN, OUTPUT);
  lcd.init();
  lcd.backlight();
  lcd.createChar(0, HEART);
  show(0);
}

void loop() {
  bool pressed = digitalRead(BUTTON_PIN) == LOW;
  bool timeUp = AUTO_MS > 0 && millis() - shownAt >= AUTO_MS;
  if (pressed || timeUp) {
    shown = (shown + 1) % COUNT;
    show(shown);
    while (digitalRead(BUTTON_PIN) == LOW) delay(10);
  }
  delay(10);
}