#include <LiquidCrystal_I2C.h>

LiquidCrystal_I2C lcd(0x20, 16, 2);

#define SET0(r,b) r&=~(1<<b)
#define SET1(r,b) r|=1<<b
#define test(r,b) (r&(1<<b))

volatile int vysledok = 0;  
volatile bool dataReady = false;  

void setup() 
{
  lcd.init();
  lcd.backlight();
  
  SET0(DDRC, 0); 
  Serial.begin(9600);
  
  SET0(ADMUX, REFS1); // voľba Aref
  SET1(ADMUX, REFS0);
  SET0(ADMUX, ADLAR); // zarovnanie nadol
  SET0(ADMUX, MUX0); // voľba kanála ADC1
  SET0(ADMUX, MUX1);
  SET0(ADMUX, MUX2);
  SET0(ADMUX, MUX3);
  SET1(ADCSRA, ADEN); // zapnutie ADC
  SET0(ADCSRA, ADATE); // spúšťanie príkazom
  SET1(ADCSRA, ADIE); // zapnutie prerušenia pri dokončení konverzie
  SET1(ADCSRA, ADPS2); 
  SET1(ADCSRA, ADPS1);
  SET1(ADCSRA, ADPS0);
  
  SET1(SREG, 7);  

  SET1(ADCSRA, ADSC);
}

void loop()
{
  if (dataReady) {
    dataReady = false; 
    lcd.home();
    lcd.print("Hodnota: ");
    lcd.print(vysledok);  
  }

  delay(100);  
}

ISR(ADC_vect) {
  vysledok = ADCL;  
  vysledok |= (ADCH << 8);  
  
  dataReady = true;

  
  SET1(ADCSRA, ADIF);  
  SET1(ADCSRA, ADSC); 
}