#include <LiquidCrystal_I2C.h>
#include <Keypad.h>

const byte ROWS = 4;
const byte COLS = 4;
char hexaKeys[ROWS][COLS] = {
  {'1', '2', '3', 'A'},
  {'4', '5', '6', 'B'},
  {'7', '8', '9', 'C'},
  {'*', '0', '#', 'D'}
};

LiquidCrystal_I2C lcd(0x27, 16, 2);
byte rowPins[ROWS] = {11, 10, 9, 8};
byte colPins[COLS] = {7, 6, 5, 4};
byte pinRelay = 2;

Keypad customKeypad = Keypad(makeKeymap(hexaKeys), rowPins, colPins, ROWS, COLS);

void setup() {
  lcd.begin(16, 2);
  lcd.clear();
  lcd.backlight();
  pinMode(pinRelay, OUTPUT);
}

int count = 0;

void loop() {
  char customKey = customKeypad.getKey();
  if (customKey) {
    if (customKey != 'C') {
      lcd.print(customKey);
      count++;
    }

    switch (customKey) {
      case '*':
        digitalWrite(pinRelay, HIGH);
        break;
      case '#':
        digitalWrite(pinRelay, LOW);
        break;
      case 'C':
        if (count > 0) {
          count--;
        }
        lcd.setCursor(count, 0);
        lcd.print(' ');
        break;
    }

    if (count >= 16) {
      count = 0;
      lcd.clear();
      lcd.setCursor(0, 0);
    }
  }
}