#define ledPin 3

int intensity = 0;
int fadeIncrement = 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, intensity);
  intensity = intensity + fadeIncrement;
  if (intensity == 0 || intensity == 255){
    fadeIncrement = - fadeIncrement;
  }
    delay(20);
}