[time-nuts] Sidereal timekeeping
iovane at inwind.it
iovane at inwind.it
Tue May 17 12:19:37 UTC 2011
Neville and Jim and all,
there are good pictures of tuning fork crystals at
I think it is the 8x3 mm in size, which is available from China (10 units for
2.5$ including worldwide shipping). Assuming as a reference the diameter of the
baseplate, say 2,5 mm without the can, the tines appear to be long in the order
of 5 mm. It looks suitable for trimming (see, just below the tuning fork
crystal, the picture of a trimmed round crystal). Trimming that way is common
practice in crystal manufacturing, and this is what happens when you order a
custom crystal (they have blanks which cover ranges). So I'm confident that the
Q will not be affected so much.
I think it is worth the try.
Anyway, Neville, as a backup solution, I would be pleased to consider your
design, and I think that others might have an interest too.
I would recall that I actually know what sidereal time it is now, by a
computer program, but my problem is that I have to rotare a mini torsion
balance by means of a low power drawing setup.
>the 32kHz Xtals are 2mm long tuning forks (that is what I believe
>although I have not opened one).
>You would have very little chance of modifying it and still have
>enough Q left for it to oscillate.
>As an alternative you could build an external circuit (a few uA at 3V
>supply) and generate a signal to inject into
>the existing Xtal osc with the Xtal removed.
>The type of circuit that I would build would be a cmos binary divider
>connected to a quad gate.
>The 4 gate inputs connect to selected binary stages of the divider.
>When the gate decodes the
>selected number, an extra pulse is added to the count chain. The
>output is thus shifted to a higher
>If you are interested I can try to design the circuit for you, I have
>intend to build a Siderial clock
>dial for my TBolt.
>cheers, Neville Michie
>On 17/05/2011, at 7:58 AM, iovane at inwind.it wrote:
>> at present I have not enough skill with micros to solve the problem.
>> I think I will try modifying a crystal. This would not be that
>> difficult using
>> a lapping sheet or the like. And opening the can would be quite
>> easy using hot
>> air. This is the fastest way for me, and the device will continue
>> to be powered
>> by a simple AA cell, which is a non negligible advantage in my
>> All the best,
>> Antonio I8IOV
>>> 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
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