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

Tom Van Baak tvb at LeapSecond.com
Thu Sep 4 21:09:30 UTC 2008


Brooke,

Here's what I did with a PIC (or Basic Stamp, etc.):

Current limit the coil to two pins of your microcontroller and
configure both as inputs (high Z).

Then for about 50 ms each second make the pins output; for
even seconds set the pins to 0 and 1; odd seconds 1 and 0.

/tvb

----- Original Message ----- 
From: "Brooke Clarke" <brooke at pacific.net>
To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
Sent: Thursday, September 04, 2008 12:25 PM
Subject: Re: [time-nuts] How to get 32.768KHz from 10MHz.


> Hi John:
> 
> All the quartz clocks I've taken apart have a single coil, for example see:
> http://www.prc68.com/I/QuartzClk.shtml
> 
> The drive to that coil is bi-polar and is from a single AA cell, so the driver 
> IC must use an H-bridge.  If you want to drive a clock like this at 1 PPS from 
> a 10 MHz source you will need to use some kind of conversion circuit.  That's 
> why it's easier to generate the 32768 Hz signal and just drive the xtal pins on 
> the  clock's IC.
> 
> Have Fun,
> 
> Brooke Clarke
> http://www.prc68.com/P/Prod.html  Products I make and sell
> http://www.prc68.com/Alpha.shtml  All my web pages listed based on html name
> http://www.PRC68.com
> http://www.precisionclock.com
> http://www.prc68.com/I/WebCam2.shtml 24/7 Sky-Weather-Astronomy Web Cam
> 
> Neon John wrote:
>> 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
>>>> 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?
>> 
>> 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
>> know.
>> 
>>> 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.
>> 
>> Comments?
>> 
>> John
>> --
>> John De Armond
>> See my website for my current email address
>> http://www.neon-john.com
>> 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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