void setup() {
  ADMUX |= B00000000; // pembacaan dilakukan di ADC0 (A0)
  ADMUX |= B10000000; // refs0 => 0 , refs1 => 1, refrensi = vcc
  Serial.begin(9600);

}

void loop() {
  
  // mulai konversi analog digital
  ADCSRA |= B11000000;
  // deteksi akhir konversi
  while (bit_is_set(ADCSRA,ADSC));
  int adc_val = ADCL | (ADCH << 8);
  float voltage = adc_val * 5.0 / 1024;
  Serial.println(voltage);
}