Progressive PWM Increase

Using Arduino Programming Questions
3

andrewf:
Hi all!
I'm new to Arduino, but am learning pretty quickly.
I was wondering if there was any way to use PWM to steadily increase something.
...
Or maybe you want the LED to increase in brightness 10% each 15 minutes that go by.
How could this be done?

Thanks!

I'm winging this off the top of my head, so here goes:

#define INTERVAL 60000     // change interval in milliseconds
#define DELTAB       25     // change in brightness

const int LedPin = 13;

int LedBrightness = 0;
unsigned long previousMillis;

void setup(void)
{
  previousMillis = millis();
  analog.write(LedPin, LedBrightness);
}

void loop(void)
{
  if (millis() - previousMillis > INTERVAL)
  {
    previousMillis = millis();
    if (LedBrightness < 256)
    {
       LedBrightness += DELTAB;
      analog.write(LedPin, LedBrightness);
     }
  }
// do other stuff here ( or not)
}

This code will start the LED off, and then once a minute (60,000 ms) increase the pulse width by DELTAB until it's full on. LED brightness may not be a linear function of pulse width. I have code very similar to this controlling the brightness of 12 volt incandescent lamps.