Using ADC of ATMega32 to adjust PWM duty cycle

In this module we have discuss about using ADC with some typical applications. Using a POT we can adjust the analog value fed to the ADC input pin manually and linearly. With this advantage we can use the ADC value to adjust the duty cycle of PWM signal.

In this example, I use ADC to vary the PWM duty cycle between 0 to 100%. The ADC value is scaled from 1024 to 100 to fit the PWM timing. PWM signal is created by timer 0 interrupt. Each interrupt occurs for every 10 micro seconds.

Schematic diagram

Source code:

#include <avr/io.h>
#include "avr/interrupt.h"
unsigned char cnt=0;
void speedControl(unsigned int speed){
 float _dutyCycle;
 unsigned int dutyCycle;
 _dutyCycle=speed*(100.0/1024);
 //dutyCycle=20;
 dutyCycle=10+(int)_dutyCycle;
 if(cnt<dutyCycle) PORTD|=(1<<0);
 if(cnt>=dutyCycle)  PORTD&=~(1<<0);
 if(cnt>=100) cnt=0;
}
int main(void)
{  unsigned int adcResult;
 //PortD as output
 DDRD=0xFF;
 //PA0 or ADC0 as an analog input
 DDRA=0;
 //Set 1:8 pre-scaler
 TCCR0=0x02;
 //Clear overflow flag
 TIFR=0x01;
 //Enable Timer 0 interrupt
 TIMSK=0x01;
 //set global interrupt
 sei();
 //Turn on the ADC module
 ADCSRA|=(1<<ADEN);
 /*Select ADC7*/
 ADMUX|=0x07;
 while (1)
 {
  //Start the conversion
  ADCSRA|=(1<<ADSC);
  //Wait for the completion
  while((ADCSRA&(1<<ADSC))==1);   //Read the result
  adcResult=ADCL+(ADCH<<8);
  speedControl(adcResult);
 }
}
ISR(TIMER0_OVF_vect){
 //Load -5 to make 10 uS interrupt time
 TCNT0=-5;
 cnt+=1;
 TIFR=0x01;
}