#define led 2

void setup() {

  Serial.begin(115200);
pinMode(led, OUTPUT);
}

void loop() {
//incremento
for(int dutycycle = 0; dutycycle < 255; dutycycle++){
  analogWrite(led, dutycycle);
  delay(1);
}

//decremento
for(int dutycycle = 255; dutycycle > 0;dutycycle--){
  analogWrite(led, dutycycle);
  delay(1);
}
}