void init_ADC(void);
void start_ADC(void);
uint16_t read_ADC(void);
void print_(uint16_t value);

void setup() {
  Serial.begin(9600);
  init_ADC();
}

void loop() {
  start_ADC();
  uint16_t x = read_ADC();
  print_(x);  // Print the ADC value
  delay(1000);  // Delay for 1 second
}

void init_ADC() {
  volatile char *admux = (volatile char *)0x7C;
  volatile char *adcsra = (volatile char *)0x7A;
  *admux = 0x40;  // Reference voltage: AVCC, ADC0 selected
  *adcsra = 0x87;  // ADC Enable, Prescaler = 128 (16 MHz / 128 = 125 KHz)
}

void start_ADC() {
  volatile unsigned char *adcsra = (volatile unsigned char *)0x7A;
  *adcsra = *adcsra | 0x40;  // Start conversion by setting ADSC bit
}

uint16_t read_ADC() {
  volatile char *adcsra = (volatile char *)0x7A;
  volatile unsigned char *L = (volatile unsigned char *)0x78;
  volatile unsigned char *H = (volatile unsigned char *)0x79;
  uint16_t value;

  while ((*adcsra & 0x10) == 0);  // Wait for conversion to complete (ADIF flag)
  value = (*H << 8) | *L;  // Combine the upper and lower bits to get the 10-bit result
  *adcsra = *adcsra | 0x10;  // Clear the ADIF flag by writing a 1 to it
  return value;
}

void print_(uint16_t value) {
  Serial.println(value);  // Print ADC value to Serial
}