[time-nuts] How to get 32.768KHz from 10MHz.
Tom Van Baak
tvb at LeapSecond.com
Thu Sep 4 17:09:30 EDT 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
>>
>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
More information about the time-nuts
mailing list