// Define LCD pins
#define RS 12
#define EN 14
#define D4 27
#define D5 26
#define D6 25
#define D7 33

// 10-digit counter
char counter[11] = "0000000000";

// Pulse enable
void lcd_pulse() {
  digitalWrite(EN, HIGH);
  delayMicroseconds(1);
  digitalWrite(EN, LOW);
  delayMicroseconds(100);
}

// Send 4 bits
void lcd_send4bits(unsigned char data) {
  digitalWrite(D4, (data >> 0) & 1);
  digitalWrite(D5, (data >> 1) & 1);
  digitalWrite(D6, (data >> 2) & 1);
  digitalWrite(D7, (data >> 3) & 1);
  lcd_pulse();
}

// Send command
void lcd_cmd(unsigned char cmd) {
  digitalWrite(RS, LOW);
  lcd_send4bits(cmd >> 4);   // higher nibble
  lcd_send4bits(cmd & 0x0F); // lower nibble
  delay(2);
}

// Send data
void lcd_data(unsigned char data) {
  digitalWrite(RS, HIGH);
  lcd_send4bits(data >> 4);
  lcd_send4bits(data & 0x0F);
  delay(2);
}

// Initialize LCD
void lcd_init() {
  pinMode(RS, OUTPUT);
  pinMode(EN, OUTPUT);
  pinMode(D4, OUTPUT);
  pinMode(D5, OUTPUT);
  pinMode(D6, OUTPUT);
  pinMode(D7, OUTPUT);

  delay(20);

  lcd_send4bits(0x03);
  delay(5);
  lcd_send4bits(0x03);
  delayMicroseconds(100);
  lcd_send4bits(0x03);
  lcd_send4bits(0x02); // 4-bit mode

  lcd_cmd(0x28); // 2 lines, 5x7
  lcd_cmd(0x0C); // display ON
  lcd_cmd(0x06); // increment cursor
  lcd_cmd(0x01); // clear display
  delay(2);
}

// Set cursor
void lcd_setCursor(int col, int row) {
  int addr = (row == 0) ? 0x80 + col : 0xC0 + col;
  lcd_cmd(addr);
}

// Print string
void lcd_print(char *str) {
  while (*str) {
    lcd_data(*str++);
  }
}

void setup() {
  lcd_init();

  lcd_setCursor(0, 0);
  lcd_print((char*)"Up Counter");

  lcd_setCursor(0, 1);
  lcd_print(counter);
}

void loop() {
  int i;

  // Increment logic
  for (i = 9; i >= 0; i--) {
    if (counter[i] < '9') {
      counter[i]++;
      break;
    } else {
      counter[i] = '0';
    }
  }

  lcd_setCursor(0, 1);
  lcd_print(counter);

  // Stop at 9999999999
  if (i < 0) {
    while (1);
  }

  delay(50); // adjust speed
}