int brightness = 0; // 0 -> (duty cycle = 0%), 255 -> (duty cycle = 100%)
const int delay_in_ms = 1000;
void setup() {
  // put your setup code here, to run once:
  pinMode(3, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  brightness = 255; // 100%
  analogWrite(3, brightness);
  delay(delay_in_ms);
  brightness = 127;  // 50%
  analogWrite(3, brightness);
  delay(delay_in_ms);
  brightness = 64;  // 25%
  analogWrite(3, brightness);
  delay(delay_in_ms);
  brightness = 0;  // 0%
  analogWrite(3, brightness);
  delay(delay_in_ms);
}