#include <stdio.h>
#include <avr/interrupt.h>


int main(void)
{
    Serial.begin(9600);

	/*
  	ADMUX |= (0<<REFS1) | (1<<REFS0) | (0<<MUX3) | (0<<MUX2) | (0<<MUX1) | (0<<MUX0);
    ADCSRA |= (1<<ADEN) | (1<<ADSC) | (1<<ADATE) |(1<<ADIE) | (0<<ADPS2) | (0<<ADPS1) | (1<<ADPS0) | (0<<ADLAR);
    ADCSRB |= (0<<ADTS2) | (0<<ADTS1) | (0<<ADTS0);
    DIDR0 |= (1<<ADC5D) | (1<< ADC4D) | (1<<ADC3D) | (1<<ADC2D) | (1<<ADC1D) | (1<<ADC0D);
    sei();
*/
		ADMUX |= (1 << REFS0); //INTERNAL REF
		ADCSRA |= (1 << ADEN) | (1 << ADSC) | (1 << ADATE) | (1 << ADIE);  // ADC ENABLE, START CONVERSION, ENABLE INTERRUPTS
		ADCSRB |= (0 << ADTS2) | (0 << ADTS1)| (0 << ADTS0);             // FREE-RUNNING MODE
		DIDR0 |= (1 << ADC0D);                                         // DISABLE DIGITAL INPUT BUFFER
		sei();


  while (1) 
  {
    //Serial.print(ADC); // to test it's running 
		
  }
}

ISR(ADC_vect) {
    Serial.println(ADC); // to test it's running 
    ADCSRA |= (1<<ADSC);
    };