#define led 9
#define pir 2
int brightness = 0;
int fadeAmount = 5;
int val = 0;

void setup() {
pinMode(led, OUTPUT);
pinMode(pir, INPUT);
Serial.begin(9600);
}

void loop() {
  val = digitalRead(pir);
  if(val == HIGH){
    lighter();
  }
 if(val == LOW){
  digitalWrite(led, LOW);
 }
}

int lighter(){
  analogWrite(led, brightness);
  brightness = brightness + fadeAmount;

  if (brightness <= 0 || brightness >= 255) {
    fadeAmount = -fadeAmount;
  }
  // wait for 30 milliseconds to see the dimming effect
  delay(30);
}