Why should the microcontroller have a crystal at all? Many have factory trimmed RC oscillators, typical 1% accuracy, because accurate timing for other than timekeeping is rarely needed. A minute per month is 10ppm, typical of a bog standard crystal, and given the choice of that or mains timing for a clock, I'd use the latter any day.
Re the power supply, they may use direct rectification from mains nowadays. Capacitive dropper and bridge with a few smoothing and surge suppression components. My 20+ year old microwave doesn't though - that has a real small transformer in it that audibly hums . Andy www.g4jnt.com On Fri, 12 Feb 2021 at 18:06, Lux, Jim <[email protected]> wrote: > > Maybe.. you've got to condition the AC from the secondary side of the > transformer and use a pin to bring it in on, which requires at least 2 > or 3 passive components, and you already have a crystal for the > microcontroller (thinking here of oven timers and the like, which have a > numeric display). These applications are super price sensitive, and > those 2 or 3 components cost money, in components, in board space, and > in assembly costs. Pennies to be sure, but... > > And the fact that my appliances drift on the order of a minute in a > month, differently. So maybe some count cycles and some have a rock. > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > <http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> Virus-free. www.avg.com <http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2> _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
