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. */
