Jinx wrote:
>
> OK, ready to do the bizzo with this ship's chronometer
>
> Basic fault is that the 5V line failed and put 30V through
> the cards. The chips are lying around dead and dying
> like a scene from Gone With The Wind. The only things
> left that I trust are the handles on the case. And I've got
> my doubts about one of those
>
> The thing will have to be virtually gutted. New PSU (NO
> convoluted voltage and current setting procedures with
> exotic transistors, just regulators) and a PIC system. The
> clocks around the ship are for the convenience of the crew
> only, they play no part in the running of the ship, but they
> must be accurate
>
> Options, in order of preference -
>
> (1) crystal oscillator, long-term accuracy implications. For
>       back-up situations only I think
>
> (2) ship's 220VAC, unsure yet of the 50Hz accuracy
>
> (3) use data from the ship's GPS system. This appeals to me
> but I know nuffink about interfacing to a GPS unit. Either I
> can get the data (RS422 ?) and extract the information, or
> detect the regular packets of data and reduce them to simple
> timing markers, unless GPS units have a handy 1Hz output
> somewhere
>
> Any comments ?


Buy a high performance crystal oven, you can
use any frequency (whatever is cheap) and use
the bresenham system to give a zero error clock.
For a lot less than a GPS you get temp compensation
and reliability. But not quite as accurate. :o)
-Roman

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