int i;
void setup() {
  // put your setup code here, to run once:
  pinMode(3, OUTPUT);
  }

  void loop() {
    // put your main code here, to run repeatedly:
    for(i=0;i<=150;i=i+1){
      analogWrite(3,i);
      delay(10);
    }
    for(i=150;i>=0;i=i-1){
      analogWrite(3,i);
      delay(10);
    }
  }