Byron A Jeff wrote:
>
> > > All this talk about clocks and 50Hz/60Hz mains
> > > timing and getting crystal clocks accurate just
> > >
> > > Using mains sync is probably the best for accuracy,
> >
> > I use this circuit as an accurate and very low power long-
> > term back-up if mains goes down or is removed during
> > transport. You can pick up a kitchen clock for $2, take the
> > small PCB out of it and unsolder the coil connection. (The
> > coil, btw, can be driven by reciprocating PIC o/ps through
> > a 390R resistor so the clock movement isn't a write-off).
> > The PCB puts out an alternating 0.5Hz on each of the two
> > pads where the coil was. Pick either as the 0V
>
> All this discussion has me rethinking my sunrise/sunset clock/controller.
> So far I'd been happy with the 32khz crystal but I haven't run tests more than
> 24 hours yet and the target location isn't going to be a well temp controlled
> as my test bench.
>
> Did we finally agree that a couple of big series resistors and a 5.1 zener
> was the safest line voltage reducer? I think I have some 1 Mohms in one of
> my junk boxes.
>
> So what do you think of the idea of counting line frequency for the primary
> timekeeper with the 32khz as the backup? I already have the 320 Khz and
> adding 2 junkbox resistors and and zener is no big deal.


If you have the option and already have a mains transformer,
that is the safest system. The large inductance of the
transformer is the best spike killer. :o)
-Roman

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