void setup() {
  // put your setup code here, to run once:
  pinMode(13, OUTPUT);
  Serial.begin(9600);
}
// 50 % Duty cant
int Duty = 0;
int tOn = 0;
int tOn1 = 0;
int tOff = 0;
int tOff1 = 0;
int PerCent = 100;
int d = 1000;

void loop(){
  for (int Duty = 0; Duty < 255; Duty ++){
  //Serial.write(Duty);
 tOn = (PerCent - Duty);
 tOn1 = tOn * d ;
 tOff = (PerCent - tOn);
 tOff1 = tOff * d;

  digitalWrite(13, HIGH);
  delayMicroseconds(tOn1);
  digitalWrite(13,LOW);
  delayMicroseconds(tOff1);
  
  tOn1 = 0;
  tOff1 = 0;
  }

  for (int Duty = 255; Duty > -1 ; Duty --){
    Serial.write(Duty);
    tOn = ((PerCent - Duty) );
    tOn1 = tOn * d;
    tOff = ((PerCent - tOn) );
    tOff1 = tOff * d;


    digitalWrite(13,HIGH);
    delayMicroseconds(tOn1);
    digitalWrite(13,LOW);
    delayMicroseconds(tOff1);
    tOn1 = 0;
    tOff1 = 0;

  }//
 
 //delay(500);
 //Serial.write(Duty);
}