ATmega168 Analog Comparator example

atmega168-analog-comparator.c

/*
  AVR ATmega168 Analog Comparator Demonstration
  by Mike Szczys
  
  I'm using a voltage divider with a photoresistor on
  PC6 and a voltage divider with equal values on PC7
  to yield a 2.5V reference signal.
  
  The analog comparator is set to throw an interrupt
  whenever there is a zero crossing. I then check the
  ACO bit to see if I should turn on LEDs on Port B or
  not.
  
  jumptuck.com

*/

#include <avr/io.h>
#include <avr/interrupt.h>

void initComparator(void){
  cli();
  ACSR |= (1<<ACIE);	//Enable analog comparator interrupt
  sei();
}

void initIO(void){
  DDRB = 0xFF;	//PortB as Outputs
  PORTB = 0xFF;	//All outputs high
}

int main(void){
  initIO();			//Initialize I/O
  initComparator();	//Initialize the analog comparator
   
  while(1){  }
}

ISR (ANALOG_COMP_vect) {
  //Check for rising or falling edge
  if (ACSR & (1<<ACO)) PORTB = 0x00;
  else PORTB = 0xFF;
}