Seconds on Clock not Counting Consistently

Projects General Guidance
1

Okay, so, my code is getting pretty long for the project I'm working on, and I'm almost positive that is the culprit for this particular issue, but I'm not sure how to resolve it! Long story short, I'm building a clock, and I want the seconds to count in the corner, while the time is listed in the center. The problem I'm having is that the seconds will not increment in consistent intervals. By that I mean that the seconds displayed don't change every second, they sometimes change even after just a fraction of a second. I'm having difficulty making this easy. I was thinking of using an interrupt to force it to increment in time with the RTC I'm using, but I'm not really comfortable with interrupts yet, and I don't want the clock to interfere with other functions. On to the code!

//RTC Variables
int rtcyear;
int rtcmonth;
int rtcday;
int rtchour;
int rtcmin;
int rtcsec;

//Subroutine to display clock values on clockscreen
void rtcClockScreenDisplay()
{
  DateTime now = rtc.now();
  boolean timeChange = true;
  boolean secondChange = true;
  int clockScreenHour;
  int clockScreenMinute;
  if (timeChange)
  {
    clockScreenHour = now.hour();
    if (clockScreenHour > 12) 
    {
      clockScreenHour = clockScreenHour - 12;
      myGLCD.setFont(DisplayFont);
      myGLCD.setColor(255, 255, 255);
      myGLCD.setBackColor(0, 0, 0);
      myGLCD.print("PM", 5, 10);
    }
    else
    {
      myGLCD.setFont(DisplayFont);
      myGLCD.setColor(255, 255, 255);
      myGLCD.setBackColor(0, 0, 0);
      myGLCD.print("AM", 5, 10);
    }
    myGLCD.setFont(ClockFont);
    myGLCD.setColor(0, 0, 0);
    myGLCD.setBackColor(255, 255, 255);
    myGLCD.print(":", 128, 80);
    clockScreenMinute = now.minute();
    if (clockScreenHour < 10)
    {
      myGLCD.printNumI(clockScreenHour, 64, 80);
    }
    else
    {
      myGLCD.printNumI(clockScreenHour, 0, 80);
    }
    if (now.minute() < 10)
    {
      myGLCD.print("0", 192, 80);
      myGLCD.printNumI(clockScreenMinute, 256, 80);
    }
    else
    {
      myGLCD.printNumI(clockScreenMinute, 192, 80);
    }
    timeChange = false;
  }
  if (now.hour() != clockScreenHour || now.minute() != clockScreenMinute)
  {
    timeChange = true;
  }
  rtcClockScreenSeconds();
}

void rtcClockScreenSeconds()
{
  int clockScreenSeconds;
  boolean secondChange = true;
  boolean secondRestart = false;
  DateTime now = rtc.now();
  clockScreenSeconds = now.second();
  myGLCD.setFont(DisplayFont);
  if (secondChange)
  {
    myGLCD.setColor(255, 255, 255);
    myGLCD.setBackColor(0, 0, 0);
    if (secondRestart)
    {
      myGLCD.setColor(0, 0, 0);
      myGLCD.fillRect(220, 190, 319, 239);
      myGLCD.setColor(255, 255, 255);
      myGLCD.setBackColor(0, 0, 0);
      myGLCD.printNumI(00, 220, 190);
      secondRestart = false;
    }
    if (clockScreenSeconds < 10)
    {
      myGLCD.printNumI(0, 220, 190);
      myGLCD.printNumI(clockScreenSeconds, 268, 190);
    }
    else
    {
      myGLCD.printNumI(clockScreenSeconds, 220, 190);
    }
    secondChange = false;
  }
  if (now.second() != clockScreenSeconds) secondChange = true;
  if (clockScreenSeconds == 0) secondRestart = true;
}

//Subroutine to display date values on datescreen
void rtcDateScreenDisplay()
{
  boolean dateChange = false;
  DateTime now = rtc.now();

  if (now.year())
  {
  }
}

//Subroutine to adjust clock values when a date change is initiated
int rtcSetDate(int yearIn, int monthIn, int dayIn)
{
  DateTime now = rtc.now();
  rtchour = now.hour();
  rtcmin = now.minute();
  rtcsec = now.second();
  rtc.adjust(DateTime(yearIn, monthIn, dayIn, rtchour, rtcmin, rtcsec));
}

//Subroutine to adjust clock value when a time change is initiated
int rtcSetClock(int hourIn, int minuteIn)
{
  DateTime now = rtc.now();
  rtcyear = now.year();
  rtcmonth = now.month();
  rtcday = now.day();
  rtcsec = 0;
  rtc.adjust(DateTime(rtcyear, rtcmonth, rtcday, hourIn, minuteIn, rtcsec));
}
2

Why all the time change stuff? Just send the time to the display. It doesn't matter whether it has changed or not, the display will still show the correct time.

3

While it does show the correct time, the display keeps flashing every time the program refreshes, which looks terrible. I only want to change the display when there is a change to record, else the whole thing is an epileptic seizure waiting to happen.

4

Ever notice how you can hear the seconds ticking past by just listening to a a clock. Every time you hear that tick you KNOW the time has changed, Even if you can't see the minute hand, hour hand or even a calendar. Somehow, that reasuring click, tells you something has changed.

5

That tick was why I chose the "if last value different from current value" format for the code, and, while it works for minutes and hours, as they aren't so noticeable to be off by a couple milliseconds, it's definitely noticeable in the seconds. Am I over complicating this?

6

You seem to be using one reading of the RTC for the general time and another for the seconds. I would expect that to give some odd figures when the two readings are either side of a specific second.

If the Arduino is doing nothing except powering the clock then you could read the RTC as often as possible and update the screen every time the seconds changes - using the same RTC value for everything.

...R

7

Hassurunous:
While it does show the correct time, the display keeps flashing every time the program refreshes, which looks terrible. I only want to change the display when there is a change to record, else the whole thing is an epileptic seizure waiting to happen.

Then your program is running too slowly. It should easily manage 50 iterations per second, a frequency undetectable to the human eye.