[time-nuts] Sidereal timekeeping

brent evers brent.evers at gmail.com
Mon May 16 13:30:14 UTC 2011


Can't you just use a programmable crystal?  Digikey will do this for
you prior to ship.  Search on crystal, then under the field type,
filter by  "Programmed by Digikey".  Four types pop up as in stock.
Not sure if they would meet you footprint requirement, but its worth a
shot.

Brent

On Mon, May 16, 2011 at 8:08 AM, Neville Michie <namichie at gmail.com> wrote:
> Antonio,
> it is quite easy to make an external circuit that uses a 32kHz  xtal and
> divides
> it down to siderial seconds. It is also easy to drive most analog quartz
> clock movements from
> an external circuit.
> Just what signal do you need? What frequency? and what does it drive? (an
> alternate polarity
> quartz clock motor?)
> It can also be done with a micro if you have the skills.
> cheers, Neville Michie
>
>
> On 16/05/2011, at 8:02 PM, iovane at inwind.it wrote:
>
>> The background of my request is an OT story. Just to mention briefly, I
>> already
>> have an ordinary (non-radio-controlled) clock machine which turns a
>> miniature
>> torsion balance in a sealed glass vessel. It runs on a single AA battery.
>> No
>> extreme accuracy needed. I wont to modify the rate to sidereal, and might
>> have
>> to replicate the setup too. I figure that the solution I should pursue is
>> getting the "odd" crystals.
>> Now it is clear to me that I have to explore two options, a) contacting a
>> crystal manufacturer, b) modifying 32768 crystals.
>> Thanks,
>> Antonio
>>
>> hmurray at megapathdsl.net wrote:
>>>
>>>> does anybody out there have any ideas as where to find a 32859Hz crystal
>>
>> (1/
>>>>
>>>> 2  that value would be better) to be used to replace 32768 crystals in
>>>> ordinary  clocks? I think that 32768 crystals cannot be dragged that
>>>> much.
>>>> I've already  read the JimLux article somewhere on the web, but I would
>>>> be
>>>> pleased finding a  simpler solution. Also, I already have computer
>>>> programs
>>>> that show sidereal  time.
>>>
>>> I think it depends upon what you mean by "ordinary clocks".
>>>
>>> Most of the recent wall clocks I've seen are battery powered (single AA)
>>> and
>>> resynchronize nightly via WWVB.
>>>
>>> If you want sidereal time, you won't have anything to synchronize to.
>>>  What
>>> sort of accuracy are you interested in?  If you want reasonable accuracy,
>>
>> you
>>>
>>> will need an external signal.  (You can provide power over the same
>>> cable.)
>>>
>>> My straw man would be to send 32859Hz down coax or twisted pair and feed
>>> it
>>> into the xtal-in pin on the clock chip.  I'm not sure how to set the
>>> time.
>>> You can cut the lead to the antenna to make sure it doesn't sync to WWVB.
>>>
>>> You can make 32859Hz from a PIC (or any micro you like) running off any
>>
>> handy
>>>
>>> frequency.  Given that this is time-nuts, I'd suggest 10 MHz from a
>>> GPSDO.
>>>
>>> It might be simpler to dump the 32KHz and WWVB chip and drive the motor
>>> directly from a 1 PPS signal.  Just use a sidereal second rather than a
>>> normal second.
>>
>>
>>
>>
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