int ledPin = 13; // using Pin 13 which is the internal LED, change this  number to drive external load

unsigned long startedTime = 0;
unsigned long currentTime = 0;
unsigned long elapsedTime = 0;
unsigned long period = 1000; // milliseconds
unsigned long switchTime = 500;
float dutyCycle = 0.5;

void setup()
{
  Serial.begin(9600);
  selectLineOne();
  Serial.println("start init.");
  delay(100);
  backlightOn();
  delay(100);
  clearLCD();
  delay(100);
  pinMode(ledPin, OUTPUT);
  delay(100);
  selectLineTwo();
  Serial.println("end   init.");
  delay(100);
}

void loop()
{
 currentTime = millis();

  elapsedTime = currentTime - startedTime;

  period = long(1000.0/readFrequency());

  switchTime = long(readDutyCycle() * float(period) + 0.5);

  if( (0 <= elapsedTime) && (elapsedTime < switchTime) )
  {
    turnLEDOnIfNotAlready();
  }
  else if( (switchTime <= elapsedTime) && (elapsedTime < period) )
  {
    turnLEDOffIfNotAlready();
  }
  else
  {
    startedTime = currentTime;
  }

  showControlValues();
  showTimeDifferencing();

}

void showControlValues()
{
    selectLineOne();
    Serial.print("F: ");
    Serial.print(readFrequency());
    Serial.print("D: ");
    Serial.print(readDutyCycle());
    Serial.println("");
    delay(100);
    
}

void showTimeDifferencing()
{
  if(elapsedTime > period)
  {
    selectLineTwo();
    Serial.print(elapsedTime);
    Serial.print("=");
    Serial.print(currentTime);
    Serial.print("-");
    Serial.print(startedTime);
  }
}

boolean isLEDOn = false;

void turnLEDOnIfNotAlready()
{
  if(!isLEDOn)
  {
    digitalWrite(ledPin, HIGH); // turn the LED ON
    isLEDOn = true;             // remember its on, so you don't tell it over and over.
  }
}

void turnLEDOffIfNotAlready()
{
  if(isLEDOn)
  {
    digitalWrite(ledPin, LOW); // turn the LED ON
    isLEDOn = false;             // remember its on, so you don't tell it over and over.
  }
}

float readFrequency() // stub for user control
{
// return(0.5);
   return(float(analogRead(0))/31.96875); // return a value between 0.0 and 32.0 Hz
}

float readDutyCycle() // stub for user control 
{
// return(0.90);
   return(float(analogRead(2))/1023.0); // return a value between 0.0 and 1.0 from analog pin 2
}

void selectLineOne()
{  //puts the cursor at line 0 char 0.
  Serial.print(0xFE, BYTE);   //command flag
  Serial.print(128, BYTE);    //position
}
void selectLineTwo()
{  //puts the cursor at line 0 char 0.
  Serial.print(0xFE, BYTE);   //command flag
  Serial.print(192, BYTE);    //position
}
void goTo(int position)
{ //position = line 1: 0-15, line 2: 16-31, 31+ defaults back to 0
  if (position<16)
  { 
    Serial.print(0xFE, BYTE);   //command flag
    Serial.print((position+128), BYTE);    //position
  }
  else if (position<32)
  {
    Serial.print(0xFE, BYTE);   //command flag
    Serial.print((position+48+128), BYTE);    //position 
  } 
  else 
  { 
    goTo(0); 
  }
}

void clearLCD()
{
  Serial.print(0xFE, BYTE);   //command flag
  Serial.print(0x01, BYTE);   //clear command.
}
void backlightOn()
{  //turns on the backlight
  Serial.print(0x7C, BYTE);   //command flag for backlight stuff
  Serial.print(157, BYTE);    //light level.
}
void backlightOff()
{  //turns off the backlight
  Serial.print(0x7C, BYTE);   //command flag for backlight stuff
  Serial.print(128, BYTE);     //light level for off.
}
void serCommand()
{   //a general function to call the command flag for issuing all other commands   
  Serial.print(0xFE, BYTE);
}