[time-nuts] driving cheap clock motors

[Mark Amos]

Neon John,

I did something similar to what you're talking about.

I wanted an analog output for a GPSDO/clock (originally based on a Brooks Shera design, but recently upgraded to a 
Thunderbolt.) I use the 1PPS GPSDO output to drive a CD4093 Schmidt trigger, which clocks a D flip flop.  I use the outputs 
of the flip flop to drive the coil that I disconnected from the cheap on-board crystal driven clock circuit. This one (like 
most of the cheap plastic movements) uses one coil - it's input reverses polarity each second.  I used an inexpensive "open 
frame" clock movement with all the gears exposed to add some aesthetic interest.  It's also an "open loop"
design - I set the time according to WWV and plug in the BNC connector between the 1 second ticks.  The Schmidt trigger and 
flip flop are wired up on a little perfboard powered from a wall wart.  I'm way overdriving the motor coil, but other than 
maybe make it a little louder, doesn't seem to be a problem.  I've mounted the movement in a cheap lacquered box.  It looks 
pretty nice. (I don't claim that it's the cheapest, best, neatest, coolest or anything elsest.  But it was fun and quick to 
put together, it works and it met my budgetary constraints...)

It's on one side of my office on a shelf. On the opposite wall is a La Crosse "atomic" radio.  People are amazed when they 
hear the two of them ticking in synchrony. Then I turn on WWV and they're even more amazed.  Of course, when I tell them 
how it all works, they look at me like I'm Doc Brown explaining a the quantum chromodynamics of a flux capacitor... 

Of course, when I tell them about some of the stuff the serious time-nuts use for time keeping they start to get that 
glazed look...

Mark  

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Message: 9
Date: Mon, 28 Jul 2008 20:08:58 -0400
From: Neon John <jgd at johngsbbq.com>
Subject: Re: [time-nuts] How to get 32.768KHz from 10MHz.
To: Discussion of precise time and frequency measurement
	<time-nuts at febo.com>
Message-ID: <idms84199nj391d5bp4e8r97hni6ado5mt at 4ax.com>
Content-Type: text/plain; charset=us-ascii

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