[time-nuts] How to get 32.768KHz from 10MHz.

[Neville Michie]

FYI,
Quartz analogue clocks almost universally use a bipolar motor, a two  
pole
magnetic circuit with the minimum reluctance axis displaced from the  
direction
of the energised field.
When activated the 2 pole magnetic rotor aligns with the magnetic  
field, when the field collapses,
the magnetic rotor moves a little towards the position of greater  
self attraction, so that it is
set up for a move in the right direction when the reverse field is  
applied.
To drive these motors as clock displays you either replicate the  
alternate 1.5 volt 20mS pulses, or connect a capacitor,
about 10 - 100 mfd in series and drive them with a 0.5 hertz square  
wave of about 1.5 volt amplitude.
The drive voltage and pulse duration should be adjusted for each type  
of motor, or else
the voltage and capacitor size so that reliable stepping occurs.  
Overdrive can stop some types as the rotor "poles".
just in case you were interested,
cheers, Neville Michie


On 29/07/2008, at 9:35 AM, Jim Lux wrote:

> At 04:22 PM 7/28/2008, you wrote:
>> On Wed, 23 Jul 2008 15:22:08 -0700, Jim Lux  
>> <James.P.Lux at jpl.nasa.gov> wrote:
>>
>>
>>>
>>> Based on the clocks I've taken apart, dividing the 10MHz down to  
>>> 1 Hz
>>> is probably your best bet, rather than trying to hit 32768. However,
>>> I don't know of a non-programmable single chip solution that will do
>>> a divide by 1E7. If you want programmable chips, there's countless
>>> ways, some more elegant than others.
>>
>> Seems to me that all the solutions proposed so far are a bit  
>> complex, trying
>> to go for the 32khz frequency when that's not necessary.  The  
>> quartz analog
>> clockworks has a one or two winding stepper motor.  The SIMPLEST  
>> solution is
>> to drive those coils directly with the PIC output and scrap the  
>> rest of the
>> circuitry.
> Actually, it's not even that complex... it's often an
> electromagnet/solenoid driving a conventional escapement type clock
> mechanism. Why use 2 coils when you don't ever need to go backwards?
>
> One advantage of generating 32kHz (averaged over 1 second) is that
> you don't have to build the power driver stage to actuate that
> electromagnet.. (since it's built into the single dirt-cheap chip in
> the clock in the first place)
>
>
>> With some clever fiddling, one could use one of the 8 pin PICs and  
>> that WOULD
>> get the solution cost down to around 50 cents :-)
>
>
> And, one could probably figure out a way to use the original 32kHz
> crystal AND run at different speeds..
>
>
>
>
>
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