My current project is to modify the software of an arduino driven clock chime so that it doesn’t keep SWMBO awake at night. The whole thing is driven from a 12v power supply which powers a stepper motor direct, and the arduino via a 7805 regulator. It is very boring to sit and watch to make sure it’s doing its thing, so I set up the serial monitor to display the minutes as they tick over. This of course requires a USB connection to the PC. All worked very nicely as long as I was doing something else on the PC, but if I went away for more than 15 minutes, the PC went to sleep, and when I woke it up the minutes count always began again at 1. It appears that the PC waking up resets the arduino. It might be that going to sleep does likewise, can’t tell. This is despite having the 7805 source of 5v continuously.  Solution is simple, tell the PC never to go to sleep,  but will I remember? Probably not, I’ll waste another hour or so working out what is going on.