#include <SoftwareSerial.h>

SoftwareSerial Serial(PB0, PB1);



bool volatile adc_done=0;
int volatile adc_Reading = 0;

void adc_setup(){


  ADCSRA |= bit(ADEN);  // Enable the ADC but does not start it. 

  ADCSRA |= bit (ADPS0);                               //   ADC clock prescalar = 2  

  ADMUX = 0; // reset ADMUX, it will sample ADC0 (PB5) by default with VCC as voltage reference..
  ADMUX |=  bit (MUX1);  // Sample PB4 

  
  ADCSRA |= bit(ADIE);                     // Enable ADC interrupt on completion. This requires global interrupt enable (I-bit in SREG, i.e., sei())

  // Optional Enable Auto Trigger Enable. This will automatically start an ADC conversion at every trigger event.
  ADCSRA |= bit(ADATE);
  ADCSRB = 0;           // Initialise ADCSR. Default trigger is Free Running mode.


}

void adc_start(){
    ADCSRA |= bit(ADSC);                     // Starts the conversion.
}


void setup(){
  Serial.begin(9600); // Must be 9600
  adc_setup();
  adc_start();
}


ISR (ADC_vect)
  {
  // Handle ADC interrupt
  adc_Reading = ADC;
  adc_done = 1;
  }  // end of ADC_vect


void loop() {
  if (adc_done){
      Serial.print("ADC reading on PB4 is: ");
      Serial.println(adc_Reading);
      adc_done = 0;
  }

}