I am trying to set up the ADC converter to work on PC5 then PC4 Basically I want to average both and then compare those averages.

Specifically, how do I tell ADSC which input to read from? Does anyone have a code example for this?

I am currently trying to build a Photovore Robot, if that helps at all.

Nevermind, I found it!

"MUX0 to MUX3 are used to select which input channel you wish to read."

If you just need to compare voltages you could use the analog comparator instead of the ADC but it doesn't do averaging.

Thanks, I am not sure which of those methods would give me a better read? Could you show an example of using the Comparator two compare two voltage sources? Even though I know the different Registers for the different pins I am having trouble figuring out how to control where the ADSC is reading from. Do I switch the bit patter by assigning it a binary value such as

ADMUX = 0011;

or something like

ADMUX |= (1<<MUX0) | (1<<MUX1);

okay, I think this will handle the problem:

uint16_t ReadADC(uint8_t __channel){
   ADMUX |= __channel;                // Channel selection
   ADCSRA |= _BV(ADSC);               // Start conversion

   while(ADCSRA & (1<<ADSC)) {
    // do nothing... just hold your breath.
  }
  // bit is cleared, so we have a result.

  // read from the ADCL/ADCH registers, and combine the result
  // Note: ADCL must be read first (datasheet pp. 259)
  uint16_t result = ADCL;
  uint16_t temp = ADCH;
  result = result + (temp<<8);
  return result;
}

}

let me know if there is a more efficient way to do it (or any glaring holes in my logic)