//By Tyler Gerritsen
//2017-11-25
//vtgerritsen@gmail.com

//Sources:
//	ATMega2560 datasheet pp.281 - 288 (http://www.atmel.com/Images/Atmel-2549-8-bit-AVR-Microcontroller-ATmega640-1280-1281-2560-2561_datasheet.pdf)
//	https://www.gammon.com.au/adc



ADCSRA =  bit (ADEN);   // turn ADC on


	//For ATMega328:
ADMUX = bit (REFS0) | (adcPin & 31);	//RES0 sets comparator ref voltage to internal vcc.  For external, 2.56v, 1.1v: See datasheet
ADCSRB = ((adcPin & 0b00100000) >> 2) + 1;

	//For ATMega2560:
ADMUX = bit(REFS0) | (adcPin * 31);		//RES0 sets comparator ref voltage to internal vcc.  For external, 2.56v, 1.1v: See datasheet
ADCSRB = ((adcPin & 0b00100000) >> 2) + 1;	//The +1 sets to one-shot mode.

//ADCSRA controls ADC state & Prescaler

bitSet(ADCSRA, ADSC);	//Begin conversion

while (!bit_is_clear(ADCSRA, ADSC)) {};		//Wait for conversion

reading = ADC;			//0 - 1023