Is there any way to count backwards on an LCD screen, as if you were making a stopwatch but with mins...
Yes, you can print anything (well more or less) on the LCD display.
You would just have to keep track of the remaining minutes in your Arduino code and display it, like you would display anything else.
Pretty easy. You could use delay and reduce a variable in a loop or something before printing it.
very often, the easiest way to do this is to represent time with some linear increment like seconds from midnight (on a particular day if you want). Then build a conversion routine that converts hours, minutes, seconds to that and vice versa.
That way, you can do math on the variable, and then convert to display.
If the only thing you want to do is count down then you can do that manually with a couple of IF statements like
seconds -= 1;
if (seconds < 0) {
seconds = 60;
minutes -=1;
if (minutes < 0) {
minutes = 60;
hours -= 1;
if (hours < 0) hours = 24;
}
}
There is no need for program control (which needs while & if), its arithmetic.
Normally, a countdown timer would have a count of, say, seconds remaining.
Assume secondsRemaining is that number.
seconds = secondsRemaining % 60; // the % operator is remainder
minutes = secondsRemaining / 60;
hours = minutes / 60;
minutes = minutes % 60; // get the left over minutes
days = hours / 24;
hours = hours % 24; // get the left over hours
WARNING - Unverify'ed and untested