On Mon, May 15, 2006 at 12:00:58PM +1200, Jinx wrote:
> > I want something I can actually get
> 
> Peter, I frequently use the guts from cheap kitchen clocks as
> the primary or back-up timing source. IME generally under
> 30s per year accuracy. I include two tact switches, '+' and '-'
> for changing the time on daylight-saving dates, and suggest that
> the clock be synched to the radio pips at the time of changing.
> Press '+' to add an hour and then, given a time limit of 1 minute
> to complete, each press of '+' or '-' will add or subtract 5 secs
> to compensate for any clock error. Output of the attached is
> 0.5Hz. The remains of the clock can still be used - drive the
> coil with two PIC pins, reciprocating style, at 1.5V. I've made
> a few novelty/special purpose clocks this way

It's an interesting idea, nice to have all that annoying timekeeping
engineering done for you already... You say they are 30s per year
accuracy... How the heck do they do that? Even the DS32khz chips aren't
that accurate, and I know cheap clocks like that use the bare
crystals... Or am I mistaking worst case performence with average?

After all, I'm sure your kitchen is 25C +- 5C :)


In any case, I think I need something a lot smaller than a kitchen
clock. My target size is to cram it all into a 1 inch by 1 inch PCB,
double sided.

-- 
pete@petertodd.ca http://www.petertodd.ca
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