int led = 9;
int brightness = 0;
int fadeAmount = 5;
void setup() {
  pinMode(led,OUTPUT);
  // put your setup code here, to run once:

}

void loop() {
  analogWrite(led,brightness);
  brightness = brightness + fadeAmount;
  if(brightness<=0 || brightness>=255)
  {
    fadeAmount = - fadeAmount;
  }
  delay(30);
  // put your main code here, to run repeatedly:

}