const int motorPin = 9;
void setup() {
  // put your setup code here, to run once:
  pinMode(motorPin, OUTPUT);
  Serial.begin(9600);
}

void loop() {

for(int i = 0; i<255; i++){
  analogWrite(motorPin,i);
  delay(10);
}
delay(100);

for(int i = 255; i>0; i--){
  analogWrite(motorPin,i);
  delay(10);
}
delay(100);
}