Well, there it is. I guess I extrapolated incorrectly from the
digital clock radios I opened up as a kid.
On Sat, Mar 10, 2018 at 11:00 PM, Levi Pearson <levipear...@gmail.com> wrote:
> On Fri, Mar 9, 2018 at 11:34 AM, Michael Torrie <torr...@gmail.com> 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:
> Here's a fun Scooby Doo Mystery Machine alarm clock with an LM8560
> mains-referenced digital clock:
> And you can see the datasheet for the LM8560 here:
> 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:
> And the part itself, with marketing blurb "Industry's Lowest Cost RTC
> Operates from 50Hz/60Hz Line Frequency":
> 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.
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