[time-nuts] Sidereal timekeeping

[Neville Michie]

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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