#include <avr/io.h>;
#include <avr/interrupt.h>

const unsigned char PS_16 = (1 << ADPS2);
const unsigned char PS_32 = (1 << ADPS2) | (1 << ADPS0);
const unsigned char PS_64 = (1 << ADPS2) | (1 << ADPS1);
const unsigned char PS_128 = (1 << ADPS2) | (1 << ADPS1) | (1 << ADPS0);



void setup()
{
  Serial.begin(1000000);
 // pinMode(A0, INPUT);


  ADCSRA &= ~PS_128;
  ADCSRA |= PS_16;


  ADMUX |= (1 << REFS0);
  ADMUX |= (1 << ADLAR); // Left adjust ADC result to allow easy 8 bit reading

  // No MUX values needed to be changed to use ADC0

  ADCSRA |= (1 << ADIE);  // Enable ADC Interrupt

  TCCR0A = 0;
  TCCR0B = 0;

  ADCSRA |= (1 << 5);  // Set ADC to Free-Running Mode
  ADCSRA |= (1 << ADEN);  // Enable ADC
  ADCSRA |= (1 << ADSC);  // Start A2D Conversions
  while(true);
   // Serial.write(analogRead(A0)>>2);
}

ISR(ADC_vect)
{
  Serial.write(ADCH);
}

void loop()
{

}