int led_pins[] = {3,5,6,9};
int num_leds = sizeof(led_pins)/sizeof(int);

void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  for (int i=0;i<num_leds;i++){
    pinMode(led_pins[i], OUTPUT);
    digitalWrite(led_pins[i], LOW);
  }
}

void loop() {
  // put your main code here, to run repeatedly:
  int timedelay = 5;

  for (int j = 0;j<num_leds;j++){
    for (int i=0;i<255;i++){
      analogWrite(led_pins[j],i);
      delay(timedelay);
    }
  }

  for (int j = 0;j<num_leds;j++){
    for (int i=255;i>=0;i--){
      analogWrite(led_pins[j],i);
      delay(timedelay);
    }
  }
  delay(1000);
  
}