Re: Looking for two-input comparator with hysteresis

On Wed, 24 May 2006 12:58:47 GMT, Fred Bloggs <nospam@xxxxxxxxxx>
wrote:


I'm building a digital clock circuit ...

Any suggestions would be much appreciated.


Any old fool can tap into that transformer to pulse a Schmitt trigger or
comparator or what have you, but tapping into the timing in such a way
that the resulting reference clock is not cumulatively "pulled" by the
DC loading of the circuit or mains variation is an entirely different
story. What is the periodicity of the mechanicals, and what is the logic
loading and its long term cycling profile? What kind of timing accuracy
are you looking for over a 24 hour period? The answer to your problem
may be much deeper than you expect.


If the schmitt is squaring up 60 Hz cycles, how can DC offsets or
"mains variations" affect clock accuracy? If you count each line cycle
exactly once (not zero times, and not twice) where's the error?

The 60 Hz line is sort of the definition of clock time.

John

.

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