byte ledPin = 9;
int brightness = 0;
int fadeAmount = 5;

void setup() {
  // put your setup code here, to run once:
  pinMode(ledPin, OUTPUT);
}

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