Arduino LCD clock not working

Question

I have this code that should display a clock on the first line of an LCD screen, and the text "Hello World" on the second line:

#include <LiquidCrystal.h>
int x=0;
int a=0;
int y=0;
int z=0;
int initialHours = 14;//set this to whatever
int initialMins = 37;
int initialSecs = 45 + 11;

int secspassed()
{
    x = initialHours*3600;
    x = x+(initialMins*60);
    x = x+initialSecs;
    x = x+(millis()/1000);
    return x;
}

int hours()
{
    y = secspassed();
    y = y/3600;
    y = y%24;
    return y;
}

int mins()
{
    z = secspassed();
    z = z/60;
    z = z%60;
    return z;
}

int secs()
{
    a = secspassed();
    a = a%60;
    return a;
}

LiquidCrystal lcd(8, 9, 4, 5, 6, 7);

void setup(){
    lcd.print("load...");
    delay(1000);
    lcd.begin(16, 2);
    lcd.setCursor(0, 1);
    lcd.print("Hello world");
}

void loop(){
    digitalClockDisplay();
}

void printDigits(byte digits){
    if(digits < 10)
        lcd.print('0');
    lcd.print(digits);
}

char sep()
{
    x = millis()/1000;
    if(x%2==0)
    {
        lcd.print(":");
    }
    else {
        lcd.print(" ");
    }
}

void digitalClockDisplay(){
    lcd.setCursor(0,0);
    printDigits(
    hours());
    sep();
    printDigits(mins());
    sep();
    printDigits(secs());
}

Instead of printing the following

12:35:15
Hello World

it prints this instead:

253:255:243
Hello World

Why?

I don't want to use the Time library, BTW.

Answer 1

The code is overflowing the capacity of an int [for arduino, that value is +/- 32767] here:

int secspassed()
{
  x = initialHours*3600;
  x = x+(initialMins*60);

At this point x should be:

14 * 3600 * 60 = 3024000

which is much bigger than the +32767 value an int can hold, and the overflow is dropped, leaving bits that represent a number of no relevance.

Should also cleanup calling the print routine with an int and casting it to a byte.

Answer 2

I've just worked out why it would be a bad idea, with rollovers and stuff. Here is the updated code for interested people:

#include <LiquidCrystal.h>

int second=0, minute=0, hour=0;
int x=0;

LiquidCrystal lcd(8, 9, 4, 5, 6, 7);

void setup(){
    lcd.print("load...");
    delay(1000);
    lcd.begin(16, 2);
    lcd.setCursor(0, 1);
    lcd.print("Hello, world ");
}

void loop(){
    static unsigned long lastTick = 0;
    if (millis() - lastTick >= 1000) {
        lastTick = millis();
        second++;
    }

    // Move forward one minute every 60 seconds
    if (second >= 60) {
        minute++;
        second = 0; // Reset seconds to zero
    }

    // Move forward one hour every 60 minutes
    if (minute >=60) {
        hour++;
        minute = 0; // Reset minutes to zero
    }

    if (hour >=24) {
        hour=0;
        minute = 0; // Reset minutes to zero
    }
    digitalClockDisplay();
}

void printDigits(byte digits){
    if(digits < 10)
        lcd.print('0');
    lcd.print(digits);
}

char sep()
{
    x = millis()/500;
    if(x%2==0)
    {
        lcd.print(":");
    }
    else{
        lcd.print(" ");
    }
}

void digitalClockDisplay(){
    lcd.setCursor(0,0);
    printDigits(hour);
    sep();
    printDigits(minute);
    sep();
    printDigits(second);
}

Have fun!

P.S.: for the updated code, go to my blog.