John,

> > The problem of building a frequency standard that is both rock-cheap in
> > cost and also accurate for long-term timekeeping is complex.

> For a device which will be powered continuously off the AC line
> (aside from momentary brief lapses) the AC line is excellent;

For my purposes, in AC only powered designs, I'm thinking about
using the AC line as a frequency standard because it would be more
precise than an external RC oscillator using 5% and 10% components.
Hey- it's a cooking appliance.  No AC, no cookie.

I don't need crystal controlled precision, but I need better than
+/-10%.      even 1% or 2% would be great.

 My question has to do with overseas 50 HZ.  Does anyone know if
they are as stable as the frequency in the US?

I need to design a system that will work on either 50 Hz or 60 Hz.
In that situation, you can't just count line pulses, you'd need to
compensate for the different frequencies as well.  I'm thinking about
a routine that measures the line frequency then decides whether it's
closer to 50 or 60 hz, then applies a software calibration number to
the timer.  Haven't thought it through at all.

Anybody done this before?

-- Lawrence Lile

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