Well, there it is. I guess I extrapolated incorrectly from the digital clock radios I opened up as a kid.
Thanks Levi Barry On Sat, Mar 10, 2018 at 11:00 PM, Levi Pearson <[email protected]> wrote: > On Fri, Mar 9, 2018 at 11:34 AM, Michael Torrie <[email protected]> wrote: > >> Yeah the folks who chose the picture to go with the article got it >> wrong! A digital clock on a microwave or stove would be timed from >> quartz crystal and wouldn't care about A/C line frequency. > > After a bit more digging, I've found that there have been cheap > integrated digital clocks with mains-frequency references for a very > long time. I've even got one kicking around here from an old digital > alarm clock/radio. There's one big chunky IC that is basically an > AM/FM radio on a chip, and another one that's basically a > mains-referenced digital clock with 7-segment display drivers. I'd be > very surprised if there weren't a couple of similar LSI clock ICs > during the 80s/90s that wer customized for appliance clock purposes > rather than alarm clocks. > > Here's a link to an old Heathkit version using a Mostek MS5071: > http://www.decodesystems.com/heathkit-clocks.html > > Here's a fun Scooby Doo Mystery Machine alarm clock with an LM8560 > mains-referenced digital clock: > http://www.toddfun.com/2014/01/12/scooby-doo-alarm-clock-repair/ > And you can see the datasheet for the LM8560 here: > http://www.paulanders.com/G5-LED/ver1/datablad.pdf > This is an obsolete part, but you can still find them online. > > And just to show that this technique is not obsolete, here's an app > note for an in-production Maxim RTC with mains-referenced timekeeping: > https://www.maximintegrated.com/en/app-notes/index.mvp/id/1994 > And the part itself, with marketing blurb "Industry's Lowest Cost RTC > Operates from 50Hz/60Hz Line Frequency": > https://www.maximintegrated.com/en/products/digital/real-time-clocks/DS1375.html > > So, I have no idea what's in modern high-tech ovens and microwaves, > but I'll bet there are still a lot of old control mechanisms still in > use on cheaper cost-optimized units and even newer ones may have > mains-referenced real-time clocks. > > --Levi > > /* > PLUG: http://plug.org, #utah on irc.freenode.net > Unsubscribe: http://plug.org/mailman/options/plug > Don't fear the penguin. > */ /* PLUG: http://plug.org, #utah on irc.freenode.net Unsubscribe: http://plug.org/mailman/options/plug Don't fear the penguin. */
