#define pb 2
#define led 3

void setup() {
  pinMode(led, OUTPUT);
  pinMode(pb, INPUT_PULLUP);  
  Serial.begin(9600);
}

void loop() {

  int buttonState = digitalRead(pb);
  int i;
  if (buttonState == LOW) {
  
    for (int i = 0; i <= 255; i += 30) {
      analogWrite(led, i);
      delay(1000);
    }
    for (int i = 255; i >= 0; i -= 30) {
      analogWrite(led, i);
      delay(1000);
    }
  } else {

    analogWrite(led, 0);
  }
}