[time-nuts] Mains Frequency

[Lux, Jim]

On 2/12/21 8:23 AM, Thomas D. Erb wrote:
> "I would think they try to hold it over 1 day, so that mains driven
>
> clocks don't run slow or fast.? That being said, I wonder how many
>
> clocks are still being built using a synchronous motor drive? Given that
>
> all the clocks on appliances in my kitchen have drifted apart, I'll bet
>
> they use their internal microcontroller crystal as a reference."
>
> Actually I think all of my kitchen appliances use line frequency for time reference - it's so easy to count.


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.