The code:
int brightness = 0;
void setup()
{
pinMode(13, OUTPUT);
}
void loop()
{
for (brightness = 0; brightness <= 255; brightness += 5) {
analogWrite(13, brightness);
delay(30);
}
for (brightness = 255; brightness >= 0; brightness -= 5) {
analogWrite(13,brightness);
delay(30);
}
}