void setup(){
 pinMode(11, OUTPUT);

}
int i=0;
int x;
void loop(){
  i = i + 1;
  analogWrite(11, i );
  delay (10);
  if (i == 255)
  {
   for (x=254; x >= 0; x--)
  {
     analogWrite(11, x );
     delay (10);
  }
    i = 0;
  }
}