[time-nuts] WWVB Signal Generator

Wayne Holder wayne.holder at gmail.com
Thu Aug 30 09:12:27 UTC 2018 

For anyone trying out my ATTiny85 code, I've done some additional tests and
find that placement of the antenna near the clock is very finicky and, so
far, the only way to get a reliable decode of the time in the clock is by
using a scope to monitor the demodulated output and then moving the antenna
around until the demodulated signal lines up cleanly with modulated carrier
and there are no intra bit glitches.  This can take a bit of patience, so
clearly a better solution needs to be found.  I've found that any type of
glitch in the demodulated signal seems to prevent the clock chip from
decoding the time.

It's possible the difficultly with locking onto my simulated WWVB signal
may be partially due to the design of the clock (from my location it's
never been able to to lock onto the real WWVB signal), but I have no
reference to compare it against so, for now, I have conclude that the
PWM-based modulation scheme my code uses may also be suboptimal for this
application.  To make testing even more frustrating, the BALDR clock I'm
using will only look for a signal for about 6 minutes before it goes to
sleep and I have to then power cycle the clock to get it to listen again.

So, keep this in mind if you're going to try and replicate my results.

Wayne

On Wed, Aug 29, 2018 at 6:03 PM Wayne Holder <wayne.holder at gmail.com> wrote:

> For those that have asked for my to publish the source code for my
> ATTiny85-based WWVB simulator, I have put up a somewhat hurriedly written
> page on my google site at:
>
>   https://sites.google.com/site/wayneholder/controlling-time
>
> that describes a bit about how the code works, how to compile it using the
> Arduino IDE, how I tested it, some issues I have observed in testing it
> and, at the bottom of the page, a downloadable zip file that contains the
> complete source code.
>
> Note: as mentioned at the top of this page, this is currently a work in
> process, so I'm not yet going to link the article to my main website page,
> so you'll need to link in this post to find it.  Also, as draft, I'm going
> to continue to revise the page until I feel the project is complete enough
> to publish.  That means the source code zip file is going to potentially
> change from time to time, too.
>
> Wayne
>
> On Wed, Aug 29, 2018 at 1:35 AM Wayne Holder <wayne.holder at gmail.com>
> wrote:
>
>> As a follow up, I now have a simple WWVB simulator written in C that's
>> now running an an ATTiny85 using nothing more than the internal, 8
>> mHz oscillator and about a 6 inch length of wire connected to one of the
>> pins as an antenna.  It generates an approximate 60 kHz signal using PWM on
>> timer 1.  I tweaked the timer value a bit to correct for some variance in
>> the internal oscillator, but I' not even sure that was necessary, as my
>> target is just a  BALDR Model B0114ST, consumer grade "Atomic" clock.
>> Modulation is done by varying the duty cycle of the PWM to approximate the
>> -17 dBr drop on the carrier.  But, again, I don't think this value is
>> critical with a consumer clock chip.  I tapped the demodulated output
>> inside the clock and displayed it on my scope along with the generated
>> signal and I got good, steady demodulation with the wire antenna just
>> placed near clock.  The next step is to connect up a GPS module and add
>> code to use it to set the time.  I'm also going to change the code to use
>> the PPS signal from the GPS to drive the output timing rather than the test
>> code I have now that uses timer 0 to generate the PPS interrupt.  I'm happy
>> to share details if anyone is interested.
>>
>> Wayne
>>
>>
>>
>> On Sun, Aug 26, 2018 at 2:51 PM, paul swed <paulswedb at gmail.com> wrote:
>>
>>> That would be a great neighbor to have but I can tell you around here its
>>> the phone. Not to concerned about someone putting up a wwvb replacement.
>>> And I can always up the power. Chickle.
>>> Regards
>>> Paul
>>>
>>> On Sun, Aug 26, 2018 at 2:34 PM, Bob kb8tq <kb8tq at n1k.org> wrote:
>>>
>>> > Hi
>>> >
>>> > The gotcha is if you have neighbors two or three doors away that *also*
>>> > put up one of
>>> > these devices. You then have a real problem with the neighbor(s) in the
>>> > middle. The
>>> > wavelength is long enough that Raleigh issues won’t get you. You still
>>> > have the two
>>> > signals ( at slightly different frequencies) beating against each
>>> other.
>>> > The result is
>>> > going to show up as who knows what to this or that receiver. With a
>>> > precision receiver,
>>> > you might even have issues from the guy two houses away …...
>>> >
>>> > Bob
>>> >
>>> > > On Aug 26, 2018, at 1:08 PM, paul swed <paulswedb at gmail.com> wrote:
>>> > >
>>> > > Agree with the conversation. With respect to neighbors when the day
>>> comes
>>> > > they may ask you to boost your signal. :-)
>>> > > Granted maybe the day won't come but at least having your local
>>> clocks
>>> > work
>>> > > is nice.
>>> > > Regards
>>> > > Paul
>>> > > WB8TSL
>>> > >
>>> > > On Sat, Aug 25, 2018 at 10:29 PM, Dana Whitlow <
>>> k8yumdoober at gmail.com>
>>> > > wrote:
>>> > >
>>> > >> With the watch being physically close to the faux WWVB
>>> "transmitter",
>>> > one
>>> > >> is in
>>> > >> the so-called "near field" regime, where the field strength (V/m)
>>> falls
>>> > as
>>> > >> the inverse
>>> > >> cube of the distance.  If one is putting the watch, say, within a
>>> few
>>> > >> inches of the
>>> > >> transmitter, reliable reception should be available yet the signal
>>> > should
>>> > >> be literally
>>> > >> undetectable by any practical receiving device more than a few feet
>>> > away.
>>> > >> Hence,
>>> > >> meeting the FCC field strength limit should be trivial.if the
>>> device is
>>> > >> used as pictured.
>>> > >> However, if one cranks up the power enough to reliably cover one's
>>> > entire
>>> > >> house,
>>> > >> then there might be a problem depending how close the nearest
>>> neighbor
>>> > >> lives,
>>> > >> even at levels well within the FCC limit he quotes.
>>> > >>
>>> > >> Taking the near field relationship in hand, 40 uV/m at 300m would
>>> > translate
>>> > >> into
>>> > >> a whopping 0.135 V/m at 20 meters range, more than enough to feed
>>> most
>>> > >> peoples'
>>> > >> entire house.  So the pragmatic issue would again be- neighbors.
>>> On the
>>> > >> other
>>> > >> hand, most of them would never be aware of the local signal as long
>>> as
>>> > they
>>> > >> get good
>>> > >> time settings, unless they live close enough to Ft. Collins for the
>>> two
>>> > >> signals to
>>> > >> contend with each other.
>>> > >>
>>> > >> It looks to me like the ferrite rod antenna is considerable
>>> overkill.
>>> > Even
>>> > >> with no
>>> > >> purposeful antenna I'd expect leakage to yield sufficient signal
>>> for at
>>> > >> least a few
>>> > >> inches.
>>> > >>
>>> > >> Dana
>>> > >>
>>> > >>
>>> > >> On Sat, Aug 25, 2018 at 8:11 PM Wayne Holder <
>>> wayne.holder at gmail.com>
>>> > >> wrote:
>>> > >>
>>> > >>> This guy has what looks like a well thought out design using a
>>> > Sirf-Based
>>> > >>> GPS and ATTiny44A chip to generate a signal to update his watch:
>>> > >>>
>>> > >>>  https://www.anishathalye.com/2016/12/26/micro-wwvb/
>>> > >>>
>>> > >>> Unfortunately, he doesn't seem to have published a schematic or his
>>> > >> source
>>> > >>> code.  But, he covers enough detail that I think it wouldn't be too
>>> > hard
>>> > >> to
>>> > >>> replicate what he's done.  Or, perhaps he would disclose these
>>> details
>>> > if
>>> > >>> contacted.
>>> > >>>
>>> > >>> Wayne
>>> > >>>
>>> > >>> On Sat, Aug 25, 2018 at 4:33 AM, D. Resor <organlists at pacbell.net>
>>> > >> wrote:
>>> > >>>
>>> > >>>> I thought I would search in a different way for a WWVB signal
>>> > generator
>>> > >>>> design.  I found this item.  While the designer explains it isn't
>>> as
>>> > >>>> accurate as WWVB it may be another starting point.
>>> > >>>>
>>> > >>>> http://www.tauntek.com/wwvbgen-low-cost-wwvb-time-
>>> > signal-generator.htm
>>> > >>>>
>>> > >>>>
>>> > >>>>
>>> > >>>> Donald R. Resor Jr. T. W. & T. C. Svc. Co.
>>> > >>>> http://hammondorganservice.com
>>> > >>>> Hammond USA warranty service
>>> > >>>> "Most people don't have a sense of humor. They think they do, but
>>> they
>>> > >>>> don't." --Jonathan Winters
>>> > >>>>
>>> > >>>> _______________________________________________
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