int led=9;
int brightness = 0;
int fadeAmount = 5;



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

void loop() {
  // put your main code here, to run repeatedly:
  analogWrite(led,brightness);
  brightness=brightness+fadeAmount;
  if(brightness<=0 || brightness>=255) {
    fadeAmount=-fadeAmount;
  }
  delay(3000);
}