Output number changes from positive to negative

[LanceRoberts]

Hi all,
A while ago I created a script to run a timer to control up to 28 relays in an infinite loop. I made the script with menus and to use a keypad to change the delays between each relay, as well as the time the individual relays will stay on. There is also a screen in the system to show what you're doing.

To start with I had the delays in seconds, but since the timings need to be more accurate I changed it to milliseconds.

I have just discovered that for some reason if I input a delay time of larger than 36767 it changes the output to a negative number and it makes the timer inoperative. (I might have that number incorrect by a few digits, forgot my paperwork at work, but it's close to that number. The first negative number I think is -36768)

The code for the Default delay (offTime) and onTime is

int onTime = 10 ; // seconds on
int offTime = 3000 ; // milliseconds off

And the part where it uses these times for the relays is, (The relays control blower motors, which is why I called it Blower)

void ManageBlowers() {
if (millis() - BlowerStartTime > offTime * 1UL)
    {
    StartBlower(CurrentBlower);
    CurrentBlower++;
    if (CurrentBlower >= BlowerCount)
      CurrentBlower=0;
    }
for (int i = 0; i < BlowerCount;i++)
  {
  if(millis()-Blowers[i].StartedTime > onTime * 1000UL)
    {
    StopBlower(i);
    }
  }
}

Can anyone help me with a reason why this is happening? My apologies if I use the incorrect terminology, but I'm very new to the Arduino coding world, and this was my first script.

Hope someone can help

[Koepel]

Could you read the next link and then explain it yourself ?
https://www.arduino.cc/reference/en/language/variables/data-types/int/

[groundFungus]

Arduino data types.

[LanceRoberts]

Thanks for the replies.
So if I understand it correctly I need to make the integer an unsigned data type? I will give this a shot in the morning when I get back to the office.
Thanks again!

[Koepel]

No !

If you do something with millis(), then use 'unsigned long'. That will go up to 50 days.

[LanceRoberts]

Sorry, was just getting to that part in the data types link sent by groundFungus. I will go through this very carefully now and try the different types for testing.
Thanks a lot

[groundFungus]

Look at the data types. An unsigned in will hold numbers 0 through 65535.

The millis() function returns unsigned long data type. For that reason, any variables used for timing are best declared as unsigned long.

[LanceRoberts]

Starting to get clear on this now, thanks for the help.