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

Jim Lux James.P.Lux at jpl.nasa.gov
Mon Jul 28 19:35:53 EDT 2008


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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