AVR Comparator C programming example

Lets write simple example on using AVR comparator module. Program is written in C and compiled with AVR-GCC compiler(WinAVR). Program example illustrates the case when Positive Comparator input is connected to Internal voltage regulator 1.23V by setting ACGB bitin ACSR register. Also as negative comparator input is taken ADC3 input via Multiplexer. As indicator LED is connected to PORTD0 pin. If input voltage is lower than 0.23V then Diode is OFF and if voltage exceed 1.23V diode lights ON. Diode state is changed with ANA_COMP_vect interrupt service routine on ACO bit toggle in ACSR register.

Working program code:

// ***********************************************************

// Project:  Analog Comparator example	

// Author: winavr.scienceprog.com	

// Module description: Analog comparator example with positive comparator

// input connected to Vref 1.23V. When compared voltage exceed 1.23V LED lighst on.

// When voltage drops bellow - LED turns OFF. Comparator inputis connected to ADC3 pin.

// ***********************************************************

#include <avr\io.h>       

#include <avr\interrupt.h>  

#define AINpin PA3

#define LED PD0

void Init(){

	DDRA&=~(1<<AINpin);//as input

	PORTA&=~(1<<AINpin);//no Pull-up

	DDRD|=(1<<LED); //Led pin as output

	PORTD|=(1<<LED);//Initally LED is OFF

	SFIOR|=(1<<ACME);//enable multiplexer

	ADCSRA&=~(1<<ADEN);//make sure ADC is OFF

	ADMUX|=(0<<MUX2)|(1<<MUX1)|(1<<MUX0); //select ADC3 as negative AIN

	ACSR|=

	(0<<ACD)|	//Comparator ON

	(1<<ACBG)|	//Connect 1.23V reference to AIN0

	(1<<ACIE)|	//Comparator Interrupt enable

	(0<<ACIC)|	//input capture disabled

	(0<<ACIS1)| //set interrupt on output toggle

	(0<<ACIS0);

	sei();//enable global interrupts

}

// Interrupt handler for ANA_COMP_vect

//

ISR(ANA_COMP_vect) {

if bit_is_clear(ACSR, ACO)

	PORTD&=~(1<<LED);//LED is ON

	else 	PORTD|=(1<<LED);//LED is OFF

}

// ***********************************************************

// Main program

//

int main(void) {

     Init();

	 while(1) {     // Infinite loop; interrupts do the rest

   }

}