void setup()
{
    pinMode(4, OUTPUT);
}
void loop()
{
for(int b=0; b<300;b++){
  analogWrite(4,b);
  delayMicroseconds(10000);
}
  for (int i = 300; i >= 0; i--) {
    analogWrite(4, i);
    delayMicroseconds(10000);
  }


}