int i = 0;
void setup() {
  // put your setup code here, to run once:
pinMode(10, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
for (i=0; i<256; i++)
{
analogWrite(10,i);
delay(5);
}
for(i=255; i>=0; i--)
{
  analogWrite(10,i);
delay(5);
}
}