Arduino上的PWM衰减LED

Question

I`m trying to blink led with PWM on Arduino, and I dont know whats wrong. But my LED is not fadeing. What is wrong? I think that I have bad registers settings, but Im not sure. Led is connected on arduino pin 11. Thank you.

#include <avr/io.h>
#include <util/delay.h>
const int delay=1000; 
void initialize_PWM()
{
    TCCR0A|=(1<<WGM00)|(1<<WGM01)|(1<<COM0A1);
    TCCR0B=1;
    DDRB|=(1<<PB3); 
}

void set_pwm(uint8_t data)
{
    OCR0A=data;
}

int main (void)
{
initialize_PWM();
uint8_t brightness=200;
while(1)
{
  for(brightness=0;brightness<255;brightness++)
  {
    set_pwm(brightness);
     _delay_ms(1);
  }

  for(brightness=255;brightness>0;brightness--)
  {
     set_pwm(brightness);
     _delay_ms(1);
 }
}
 return 0;
}

Answer 1

Have you looked at the 'Fade' example program?

/*
 Fade

 This example shows how to fade an LED on pin 9
 using the analogWrite() function.

 This example code is in the public domain.
 */

int led = 9;           // the pin that the LED is attached to
int brightness = 0;    // how bright the LED is
int fadeAmount = 5;    // how many points to fade the LED by

// the setup routine runs once when you press reset:
void setup()  { 
  // declare pin 9 to be an output:
  pinMode(led, OUTPUT);
} 

// the loop routine runs over and over again forever:
void loop()  { 
  // set the brightness of pin 9:
  analogWrite(led, brightness);    

  // change the brightness for next time through the loop:
  brightness = brightness + fadeAmount;

  // reverse the direction of the fading at the ends of the fade: 
  if (brightness == 0 || brightness == 255) {
    fadeAmount = -fadeAmount ; 
  }     
  // wait for 30 milliseconds to see the dimming effect    
  delay(30);                            
}

See http://arduino.cc/en/Tutorial/Fade

Answer 2

Your code seems correct, but you are using timer0, that can generate pwm on Arduino UNO's pin 5 and 6, as shown in the datasheet. So you should set the ddrd bit 6 with a DDRD |= (1 << PD6) , that is pin 6 on Arduino, not pin 11. If you want pwm on pin 11 you should use timer2 instead.