Millis (); won't work properly

Projects Programming
30

Here's a duty cycle sketch to play with:

/*
 Enter Hz in Serial monitor with h followed by number like this:
   h20{ENTER]
 Enter percent like:
   p50[ENTER]
 Or both:
 h20,p50[ENTER] 
 */
 
unsigned long cycleStart,
              onTime,              
              cycleTime,
              hz;
int val;              
const byte powerPin = LED_BUILTIN;
byte percent = 50;
void setup()
{
  Serial.begin(9600);
  Serial.println(" Hz = 5  Duty Cycle = 50%");
  hz = 5;
  cycleTime = 1000000UL / hz;
  onTime = cycleTime / 2;  
  pinMode(powerPin,OUTPUT);
}
void loop()
{
  digitalWrite(powerPin,micros() - cycleStart < onTime);  
  if(micros() - cycleStart > cycleTime)
    cycleStart += cycleTime;
  // if there's any serial available, read it:
  if(Serial.available() > 0)
  {
     val = Serial.read();
    if(val == 'h' || val == 'H')
      hz = Serial.parseInt();
    else if(val == 'p' || val == 'P')
    {
      percent = Serial.parseInt();   
    }
    else
      while(Serial.available() > 0)
        Serial.read();  
    cycleTime = 1000000UL / hz;
    percent = constrain(percent, 0, 100);
    onTime = cycleTime * 0.01 * percent;
    cycleStart = micros();
    Serial.print(" Hz = ");
    Serial.print(hz);
    Serial.print("  Duty Cycle = ");
    Serial.print(percent);
    Serial.println("%");
  }
}