>On Mon, 10 Mar 1997, TONY NIXON 54964 wrote:
>
>> I need to make a clock that is accurate. It will be powered by the
>> mains, and I thought of using this as a time base as it is a fairly
>> stable waveform.


>hello,
>        i don't think using the mains for refrence frequency will give
>you a stable clock. if you are using PIC for the clock the best idea is
>to put it in some delay loop and keep on counting the number of passes.
>PIC being driven by a crystal oscillator will give much more stable clock.
>
>vishram.

My opinion, for what its worth, is that the AC mains in North America is
EXTREMELY accurate and quite suitable for a clock timebase.  Power
generating utilities (agin, in North America) generally use atomic clocks to
ensure accuracy.  A clock that shows consistant time errors usually does not
filter the noise present on the AC mains enough and it is the noise spikes
that mess up the accuracy.  As I said, just my opinion.  I have built clocks
that, except for power outages (I suppose that you could consider THAT to be
an extensive noise spike!), have not deviated by more than 1 second over
several months.

Dwayne Reid   <dwayner@planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, Alberta, CANADA
(403) 489-3199 voice     (403) 487-6397 fax