#include <LiquidCrystal_I2C.h>

LiquidCrystal_I2C lcd(0x27, 16, 2);

#define ENCODER_CLK 2
#define ENCODER_DT 3
#define ENCODER_SW 4

int counter = 0;

void setup() {

  lcd.init();
  lcd.backlight();

  pinMode(ENCODER_CLK, INPUT);
  pinMode(ENCODER_DT, INPUT);
  pinMode(ENCODER_SW, INPUT_PULLUP);
  attachInterrupt(digitalPinToInterrupt(ENCODER_CLK), readEncoder, FALLING);
}

void loop(){
  int dtValue = digitalRead(ENCODER_DT);
  if (dtValue == HIGH) {
    counter++;
  }
  if (dtValue == LOW) {
    counter--;
  }
}