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

Neon John jgd at johngsbbq.com
Mon Jul 28 20:08:58 EDT 2008

On Mon, 28 Jul 2008 16:35:53 -0700, Jim Lux <James.P.Lux at jpl.nasa.gov> wrote:

>>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
>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?

The clockworks that I've taken apart almost all have 2 coils.  One brand has
one. They all drive a permanent magnet rotor that turns 90 degrees on each
tick.  I'm not sure what the single coil design does to make sure the rotor
always turns the right direction.  Or maybe it doesn't matter if the rotor
turns a cam and ratchet mechanism.  I've never taken one apart far enough to

>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)

No driver needed.  Each coil has about a bazillion (bazillion.000000 for time
nuts) turns of wire so fine I can't see it without my 7x OptiVisor.  I've
never bothered to measure but the resistance has to be in the hundreds of ohms
or more.  It has to be that high to get over a year's operation from an AA
battery.  Duck soup for a PIC output pin driver.

Funny how this works.  I've been thinking about this same type problem for a
few days independent of reading this list.  I'm old-fashioned and like analog
clocks much better than digital.  I also like the precision of
radio-controlled clocks.  I've bought several different WWVB analog clocks,
all of which seem to use the same cheap ChiCom movement.  They uniformly suck
(to use a technical term) at receiving WWVB where I live.  The digital
versions have no problem receiving but I don't like the looks.

What I've been thinking about is a modern version of the Simplex master/slave
clock system.  A GPS disciplined master clock sending out operating pulses to
slave clocks around my house and shop.

I thought about wireless, including synthesizing my own WWVB signal but I know
that I'll not get enough round tuits to do that.  What I'm working toward is
just about what I described above, except that the master clock will drive 4
conductor telephone station wire and the slave clocks will contain no
electronics.  Only the clockwork and the coils.  All the clocks will be wired
in parallel.

This is an open-loop system that assumes all the clocks are in the same
mechanical position when the master is activated.  Perfectly acceptable, given
the relatively few number of clocks and the small area involved.

This architecture should give me what I want - REALLY simple, no electronics
in the individual clocks, "atomic" accuracy, automatic DST correction and
perfect synchronism.


John De Armond
See my website for my current email address
http://www.johndearmond.com <-- best little blog on the net!
Tellico Plains, Occupied TN
No one can be right all of the time, but it helps to be right most of the time. -Robert Half

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