int led = 4 ;
int pwm ;
void setup() {
 pinMode(led , OUTPUT);
  Serial.begin(115200);
}

void loop() {

  
  for (int i = 0; i<=10;i++){
   Serial.println(pwm);
   pwm = map(i ,0,10,0,255);
   analogWrite(led,pwm);
   delay(50);
  }
  
  for (int i = 10; i>=0;i--){

   Serial.println(pwm);
   pwm = map(i ,0,10,0,255);
   analogWrite(led,pwm);
   delay(50);
  }

  
}