Re: [time-nuts] 1PPS to 32.768 khz

[Chris Albertson]

I think the suggestion to simply blast out 32768 pulses once per second at
a fast rate of (say) 40kHz is the simplest yet and VERY close to what the
OP asked for.   This makes the average frequency near perfect but of cours
with HORRIBLE phase noise but the OPonly cares about average frequency.

It would be VERY easy to program a small micro controller to output 32768
pulses on an output pin whenever a PPS is detected on an input pin.I
could implement this in a bare 8-pin AVR chip in about 15 minutes.The
chip would only need 5 volts power and ground.  The 32KHz signal would have
very poor short term characteristics but who cares?

I was about to write that is is theoretically impossible to create 32kHz
from 1Hz (PPS) and I stick by that.  (but notice in the above we don't
create 32kHz  we just output a fixed number of pulses that have some
imprecise timing then wait for the nest second "tick".

Back to creating 32K for 1Hz.  It is impossible, even in theory.  The best
you can do is output a signal you hope is very close to 32kHz, measure it
relative to the 1PPS reference then adjust it to make it closer to 32kHz
and keep on adjusting it every second.  It will never be perfect.

But the crude 8-pin AVR chip would be as good as at the 1PPS reference,
better on average then any GPSDO.





On Wed, Oct 19, 2016 at 8:07 PM, David  wrote:

> I was thinking 32.768kHz VCXO and phase detector to make a simple
> analog PLL.  I found a datasheet for a suitable VCXO and assuming a
> total error of 20ppm, it would only need to be divided by 2 to prevent
> locking to the wrong frequency making an analog PLL pretty simple.
> Safer to divide by 4 or 16 of course.
>
> But I wonder if a microcontroller using a 32.768kHz external clock
> could be the phase detector itself.  Strobe the microcontroller ADCS
> from the 1 PPS to sample the sine 32.768kHz clock, simmer, and serve.
> Or just count cycles to make a FLL.
>
> The most annoying thing about using a varactor for tuning is that they
> are not amendable to low drive voltages.
>
> On Wed, 19 Oct 2016 18:14:32 -0400, you wrote:
>
> >Hi
> >
> >As has been already mentioned, a lot depends on what you have. The drop
> dead cheapest way to do it:
> >
> >Start with an MCU with an internal oscillator. There are *lots* to pick
> between. Which sort really does not matter.
> >For example, I’ll use one that starts at 4 MHz.
> >
> >Divide the 4 MHz down to 32,768, or as close as you can get. The common
> clocks aren’t going to divide
> >straight to 32768 so you will need to do two divides. One will be a bit
> fast, the other a bit slow. You flip between the
> >two in a fixed pattern to get the result to average out correctly.
> >
> >Next take the same 4 MHz and run a counter /timer off of it. Capture the
> pps edge with the timer. It will drift
> >a bit since the clock in the MCU is not perfect. Based on the drift,
> modify your dividers to correct the outcome.
> >If you are “good” to 1 part in 32,768 in each second, that’s close enough
> for a wall clock. You will have no net
> >error long term if you do it right.
> >
> >That’s all a sub $1 solution….
> >
> >Bob
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-- 

Chris Albertson
Redondo Beach, California
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Re: [time-nuts] 1PPS to 32.768 khz

[Robert LaJeunesse]

One needs to be careful when generating the 32.768KHz signal. If it's used to 
clock a PLL internal to the clock's microcontroller then providing a the right 
pulse count, at the wrong frequency and interrupted, could result in poor or no 
clock operation. If it drives the display multiplexing there could be 
unpleasant "breathing" of the display intensity. If it just drives a counter, 
no big concern. 

(Me, I'd consider a small microcontroller that's crystal clocked at 8.388 MHz 
and divided down by 128 (+/-1 or 0) to create the required output edge. Also 
divide that by 256*256 to create a signal that gets compared to the 1 Hz 
reference. Based on the comparison adjust the (+/-1 or 0) for the next half 
cycle as need be to phase lock.)

Bob LaJeunesse

> Sent: Wednesday, October 19, 2016 at 7:15 PM
> From: "Mark Sims" 
> To: "time-nuts@febo.com" 
> Subject: [time-nuts] 1PPS to 32.768 khz
>
> Here's another way to do it for a wall clock display...   set up an 
> oscillator/divider (or even a 555 timer) to generate a frequency close to, 
> but faster than 65536 Hz.Setup a 16 bit counter clocked by that signal. 
> When the 1PPS signal arrives, start the counter.  After 65536 pulses the 
> counter will overflow... stop the counter (and set up for the next 1PPS 
> trigger) when that happens.   The Q0 output (lowest bit) from the counter 
> will be a burst of 32768 pulses that repeats once a second.  Use that to 
> drive your clock.   The slight pause between bursts of 32768 pulses will not 
> be noticed on the clock display.
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[time-nuts] 1PPS to 32.768 khz

[Lee - N2LEE via time-nuts]

Tom nailed the issue.

First problem is I was native in thinking “Oh this will be easy to interface to 
the NTP or GPS”.  WRONG  :) 
But the good news I am learning a lot about accurate time from you guys.

The second issue is Tom is right. This is a cheap jumbo clock that at the heart 
uses a Holtek HT48R30A
8 bit processor. Everything is contained in the chip except the 32khz crystal 
and led drivers.

http://pdf1.alldatasheet.com/datasheet-pdf/view/82435/HOLTEK/HT48R30A.html

This is certainly not the most sophisticated clock chip available.

My original idea was to hijack the timing signal and replace it with something 
more accurate. But the more info
you guys share the more I see there are a couple of ways to do this. Obviously 
the easiest might be to just replace the
crystal with a TCXO and hope for the best. But my guess as soon as it is off by 
one second from my other sources I will
be back into tearing it apart again. LOL

A lot of my other clocks are 6 digit NTP POE clocks so they are not GPS 
accurate but I would at like them to all agree.

Lee - N2LEE



Right, but that trick only works with analog stepper motor clocks. OP has a 
"big digital clock" with 8-bit cpu and 32 kHz xtal. He didn't mention the 
make/model of digital clock but in my experience very few commodity clocks 
actually accept a 1PPS input. These clocks use 32 kHz:

1) to drive the MCU which computes day / date / hh:mm:ss, or manages alarms
2) to maintain timekeeping
3) to multiplex digits of the LED / LCD display (e.g., at 128 to 1024 Hz)
4) to create the short bipolar stepper motor pulse (e.g., 1/32 kHz * 512 = 1/64 
s = 15.6 ms).
5) to create the sound for the alarm/buzzer (some PWM based on 32 kHz)

The problem is that all these functions are usually integrated into one chip or 
even raw die/epoxy as in COB (Chip On Board). When hacking these sort of clocks 
it is often impossible to separate 32 kHz frequency features from the 1 Hz 
timing feature.

So when your goal is to improve timekeeping accuracy in these self-contained 
digital clocks it's usually easier and less invasive to make the clock use your 
precise 32 kHz signal instead of its own cheap xtal. You almost always have 
access to the xtal, but rarely access inside the MCU.

Note that you don't even need to unsolder the xtal -- you can "jam" the 
existing signal with an external 32 kHz sine or square wave applied to the XI 
pin (xtal in) of the MCU. Your external GPSDO/32kHz signal will "pull" the 
cheap xtal for free. Best yet, if your external signal goes away the clock 
keeps running using its own xtal without skipping a beat, like getting 
hold-over for free.

For a "no solder" or "no wires" solution, I have also tried to acoustically 
discipline a tuning fork xtal with an GPS-based 32 kHz signal and ultrasonic 
transducer. Poor results. I think I needed better coupling between the 
transducer and the xtal tuning fork. But in theory it should work. Plus it 
would keep small mammals and insects away from your clock.

/tvb

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Re: [time-nuts] 1PPS to 32.768 khz

[David]

I was thinking 32.768kHz VCXO and phase detector to make a simple
analog PLL.  I found a datasheet for a suitable VCXO and assuming a
total error of 20ppm, it would only need to be divided by 2 to prevent
locking to the wrong frequency making an analog PLL pretty simple.
Safer to divide by 4 or 16 of course.

But I wonder if a microcontroller using a 32.768kHz external clock
could be the phase detector itself.  Strobe the microcontroller ADCS
from the 1 PPS to sample the sine 32.768kHz clock, simmer, and serve.
Or just count cycles to make a FLL.

The most annoying thing about using a varactor for tuning is that they
are not amendable to low drive voltages.

On Wed, 19 Oct 2016 18:14:32 -0400, you wrote:

>Hi
>
>As has been already mentioned, a lot depends on what you have. The drop dead 
>cheapest way to do it:
>
>Start with an MCU with an internal oscillator. There are *lots* to pick 
>between. Which sort really does not matter. 
>For example, I’ll use one that starts at 4 MHz. 
>
>Divide the 4 MHz down to 32,768, or as close as you can get. The common clocks 
>aren’t going to divide
>straight to 32768 so you will need to do two divides. One will be a bit fast, 
>the other a bit slow. You flip between the 
>two in a fixed pattern to get the result to average out correctly. 
>
>Next take the same 4 MHz and run a counter /timer off of it. Capture the pps 
>edge with the timer. It will drift
>a bit since the clock in the MCU is not perfect. Based on the drift, modify 
>your dividers to correct the outcome. 
>If you are “good” to 1 part in 32,768 in each second, that’s close enough for 
>a wall clock. You will have no net
>error long term if you do it right. 
>
>That’s all a sub $1 solution….
>
>Bob
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Re: [time-nuts] 1PPS to 32.768 khz

[Chris Albertson]

I think the way you drive the clock with a 1PPS signal is to trash the
existing controller.  Then get some Arduino-like board and connect each LED
to one of the board's output pins and the PPS to one of the boards
interrupt pins.   You replace the entire controller.   They don't cost.
Cheaper than building a GPSDO

On Wed, Oct 19, 2016 at 1:51 PM, Tom Van Baak  wrote:

> Hi Brooke,
>
> > So why not bypass the 32768 and drive the clock directly from the 1 PPS
> you now have.
>
> Right, but that trick only works with analog stepper motor clocks. OP has
> a "big digital clock" with 8-bit cpu and 32 kHz xtal. He didn't mention the
> make/model of digital clock but in my experience very few commodity clocks
> actually accept a 1PPS input. These clocks use 32 kHz:
>
> 1) to drive the MCU which computes day / date / hh:mm:ss, or manages alarms
> 2) to maintain timekeeping
> 3) to multiplex digits of the LED / LCD display (e.g., at 128 to 1024 Hz)
> 4) to create the short bipolar stepper motor pulse (e.g., 1/32 kHz * 512 =
> 1/64 s = 15.6 ms).
> 5) to create the sound for the alarm/buzzer (some PWM based on 32 kHz)
>
> The problem is that all these functions are usually integrated into one
> chip or even raw die/epoxy as in COB (Chip On Board). When hacking these
> sort of clocks it is often impossible to separate 32 kHz frequency features
> from the 1 Hz timing feature.
>
> So when your goal is to improve timekeeping accuracy in these
> self-contained digital clocks it's usually easier and less invasive to make
> the clock use your precise 32 kHz signal instead of its own cheap xtal. You
> almost always have access to the xtal, but rarely access inside the MCU.
>
> Note that you don't even need to unsolder the xtal -- you can "jam" the
> existing signal with an external 32 kHz sine or square wave applied to the
> XI pin (xtal in) of the MCU. Your external GPSDO/32kHz signal will "pull"
> the cheap xtal for free. Best yet, if your external signal goes away the
> clock keeps running using its own xtal without skipping a beat, like
> getting hold-over for free.
>
> For a "no solder" or "no wires" solution, I have also tried to
> acoustically discipline a tuning fork xtal with an GPS-based 32 kHz signal
> and ultrasonic transducer. Poor results. I think I needed better coupling
> between the transducer and the xtal tuning fork. But in theory it should
> work. Plus it would keep small mammals and insects away from your clock.
>
> /tvb
>
> - Original Message -
> From: "Brooke Clarke" 
> To: "Lee - N2LEE" ; "Discussion of precise time and
> frequency measurement" 
> Sent: Wednesday, October 19, 2016 12:18 PM
> Subject: Re: [time-nuts] 1PPS to 32.768 khz
>
>
> Hi Lee:
>
> 32768 can easily be divided down to drive the clock.  So why not bypass
> the 32768 and drive the clock directly from the
> 1 PPS you now have.
> http://www.prc68.com/I/QuartzClk.shtml
>
> --
> Have Fun,
>
> Brooke Clarke
> http://www.PRC68.com
> http://www.end2partygovernment.com/2012Issues.html
> The lesser of evils is still evil.
>
>  Original Message 
> > First let me say this is first time I have posted to the group so go
> easy on me. :)
> > Secondly I want everyone to know that you guys make me feel so NORMAL for
> > wanting to use and understand accurate timing devices.
> >
> > I thought there was something seriously wrong with me now I know there
> are others
> > affected with the same disease. hehe
> >
> > Now my questions.
> >
> > 1. Does anyone know of a device that will take a 1PPS GPS timing signal
> and generate a 32.768 kHz sine wave output ?
> > I have big digital clock that uses an 8 bit micro processor and an
> external 32.768 crystal. Obviously the external crystal is
> > awful for accuracy.
> >
> > I have searched every where using as many search terms as I can think of
> and can’t believe there is not a device that performs
> > this function.
> >
> > I have found a couple of Epson RTC chips that might come close that 1pps
> but I don’t think that corrects the 32khz just the clock time.
> >
> > 2. 10 Mhz Freq Standard
> > I am not in the same league as the majority of the list members and just
> starting to dabble in GPSDO stuff.
> > I have tried to find a thunderbolt as a starting device but it appears
> those are either dried up or people want too much money.
> >
> > I wanted to get the opinion of anyone who has tried the Leo Bodnar GPSDO
> ?
> > For the money it appears to offer a beginner a lot of features.
> >
> > Thanks and reading the daily digest of what you guys are working on.
> > I have a feeling if I am not careful you guys could cost me a lot of
> money. hehe
> >
> >
> > Lee
>
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> To unsubscribe, go to https://www.febo.com/cgi-bin/
> mailman/listinfo/time-nuts
> and follow the instructions there.
>



-- 

Chris Albertson

Re: [time-nuts] PC clock generator without 14.318MHz

[Chris Albertson]

The last time I read about this it was on an ARM based board.  They clocked
it with a GPSDO.   I think the problem is MUCH easier if you can abandon
the PC platform.

The other story I read solved to problem by adding even more hardware and
some software changes.  They moved the nanosecond counter out of the CPU
chip to a hardware counter and then the PPS signal connected to a latch.
This avoids the interrupt latency.

In most normal NTP servers the interrupt causes the CPU to snapshot its
internal nanosecond counter and store the snapshot in memory and set a flag
so the user space task can then read the value stated in RAM.   This gets
you only microsecond resolution.

With special hardware the counter is latched with external hardware then
then on the interrupt handler only has read the latch and place that valuer
in RAM and set the same flag. The trouble is that EVERY routine that
reads the internal counters has to by modified to read the eternal counter.
   As I remember these system ran BSD UNIX.

On Wed, Oct 19, 2016 at 9:02 AM, Vladimir Smotlacha  wrote:

>
> On 10/18/2016 11:23 PM, Mike Cook wrote:
>
>>
>> Le 18 oct. 2016 à 16:53, Vladimir Smotlacha  a écrit :
>>>
>>>
>>>
>>> Hello,
>>>
>>> I have operated own NTP servers with stable system clock for many years.
>>> The principle is quite simple - I replaced 14.318 MHz quartz with OCXO
>>> based circuit. Now I have to build few more servers with modern mini-ITX
>>> motherboards, however on many of them (e.g. from ASUS) I can’t find any
>>> 14.317 MHz quartz.  Such frequency is a relic of original PC design and I
>>> wonder if it is used any other basic frequency in recent clock generators?
>>>
>>
>> The 14.317MHz xtal was connected to the south bridge controller chip, but
>> for recent CPUs this has gone away as has northbridge and the system clock
>> has been integrated into the PCH (Platform Controller Hub) chip according
>> to Wikipedia, so I suspect that if you find the clock feeding that , then
>> you could stabilize it in that same way.
>>
>>
> Thank you Mike, PCH will be object of my experiments.
> I wonder than probably nobody solved stable clock source in "post 14.318"
> mainboards.
>
> Vladimir
>
>
>>> thanks,
>>> Vladimir
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>>> ailman/listinfo/time-nuts
>>> and follow the instructions there.
>>>
>>
>> "The power of accurate observation is commonly called cynicism by those
>> who have not got it. »
>> George Bernard Shaw
>>
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-- 

Chris Albertson
Redondo Beach, California
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Re: [time-nuts] 1PPS to 32.768 khz

[Hal Murray]

> Here's another way to do it for a wall clock display...   set up an
> oscillator/divider (or even a 555 timer) to generate a frequency close to,
> but faster than 65536 Hz.Setup a 16 bit counter clocked by that signal.
> When the 1PPS signal arrives, start the counter.  After 65536 pulses the
> counter will overflow... stop the counter (and set up for the next 1PPS
> trigger) when that happens.   The Q0 output (lowest bit) from the counter
> will be a burst of 32768 pulses that repeats once a second.  Use that to
> drive your clock.   The slight pause between bursts of 32768 pulses will not
> be noticed on the clock display. 

Neat hack.  Thanks.

You can do it with a tiny micro.  Some of them come with builtin R-C 
oscillators so the parts count would be really low.


-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] 1PPS to 32.768 khz

[Bob Camp]

HI

That approach would also work fine on a “internal clock” MCU. Scratch the need 
for a fancy timer. You may
be down under 50 cents ….

Bob


> On Oct 19, 2016, at 7:15 PM, Mark Sims  wrote:
> 
> Here's another way to do it for a wall clock display...   set up an 
> oscillator/divider (or even a 555 timer) to generate a frequency close to, 
> but faster than 65536 Hz.Setup a 16 bit counter clocked by that signal. 
> When the 1PPS signal arrives, start the counter.  After 65536 pulses the 
> counter will overflow... stop the counter (and set up for the next 1PPS 
> trigger) when that happens.   The Q0 output (lowest bit) from the counter 
> will be a burst of 32768 pulses that repeats once a second.  Use that to 
> drive your clock.   The slight pause between bursts of 32768 pulses will not 
> be noticed on the clock display.
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[time-nuts] 1PPS to 32.768 khz

[Mark Sims]

Here's another way to do it for a wall clock display...   set up an 
oscillator/divider (or even a 555 timer) to generate a frequency close to, but 
faster than 65536 Hz.Setup a 16 bit counter clocked by that signal. When 
the 1PPS signal arrives, start the counter.  After 65536 pulses the counter 
will overflow... stop the counter (and set up for the next 1PPS trigger) when 
that happens.   The Q0 output (lowest bit) from the counter will be a burst of 
32768 pulses that repeats once a second.  Use that to drive your clock.   The 
slight pause between bursts of 32768 pulses will not be noticed on the clock 
display.
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[time-nuts] Fwd: TNS-BUF High Isolation, Low Noise Buffer Amp Available

[John Ackermann N8UR]

We've received enough orders to go ahead with production on the TNS-BUF, 
so here's your last chance to join the cool kids -- we'll take orders at 
http://tapr.org/kits_tns-buf through tomorrow, Oct. 20.


John
 Forwarded Message 
Subject: [time-nuts] TNS-BUF High Isolation, Low Noise Buffer Amp Available
Date: Wed, 5 Oct 2016 10:15:46 -0400

I've previously mentioned a high performance buffer amplifier called the
"TNS-BUF" that I built based on a design by Dr. Bruce Griffiths with
further input from John Miles. Key numbers are:

*  Phase noise -140dBc/Hz at 1 Hertz offset, noise floor -175dBc/Hz.
(PN plot attached)
*  Reverse isolation greater than 100dB; low enough that I can't make a
trustworthy measurement.
*  Gain from -10 to +7 dB from 1 to 30 MHz; maximum output >18dBm.
*  Nominal 18VDC operation, but works down to 12V with lowered
maximum output level.

There's information, including performance data and schematic, at
http://www.febo.com/pages/TNS-BUF

There seems to be some interest in an amplifier like this, so TAPR has
decided to do a limited production run.  The amp is built with surface
mount parts, so we thought an assembled and tested board was better than
a kit.  The price will be $119 each.  But we have no idea how much
interest there is, and we need to build a minimum of 25 units to make
production feasible.

So, here's the deal:  you can order your TNS-BUF at

http://tapr.org/kits_tns-buf

through *October 20*.  If we receive orders for at least 25 boards by
then, we will charge credit cards and place the production order with
our contract manufacturer.  If we don't get 25 orders, we'll cancel the
project and credit cards will not be charged.  There's no guarantee that
boards will be available for later order.

We expect about 60 days between placing the manufacturing order and
receipt of the boards at TAPR.  We'll ship to customers ASAP after
receipt.  So that means you can expect to receive your order shortly
after January 1.

So, go to http://tapr.org/kits_tns-buf now to place your order before
the deadline!

John




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Re: [time-nuts] 1PPS to 32.768 khz

[Bob Camp]

Hi

As has been already mentioned, a lot depends on what you have. The drop dead 
cheapest way to do it:

Start with an MCU with an internal oscillator. There are *lots* to pick 
between. Which sort really does not matter. 
For example, I’ll use one that starts at 4 MHz. 

Divide the 4 MHz down to 32,768, or as close as you can get. The common clocks 
aren’t going to divide
straight to 32768 so you will need to do two divides. One will be a bit fast, 
the other a bit slow. You flip between the 
two in a fixed pattern to get the result to average out correctly. 

Next take the same 4 MHz and run a counter /timer off of it. Capture the pps 
edge with the timer. It will drift
a bit since the clock in the MCU is not perfect. Based on the drift, modify 
your dividers to correct the outcome. 
If you are “good” to 1 part in 32,768 in each second, that’s close enough for a 
wall clock. You will have no net
error long term if you do it right. 

That’s all a sub $1 solution….

Bob

> On Oct 18, 2016, at 10:03 PM, Lee - N2LEE via time-nuts  
> wrote:
> 
> First let me say this is first time I have posted to the group so go easy on 
> me. :)
> Secondly I want everyone to know that you guys make me feel so NORMAL for
> wanting to use and understand accurate timing devices.
> 
> I thought there was something seriously wrong with me now I know there are 
> others
> affected with the same disease. hehe
> 
> Now my questions.
> 
> 1. Does anyone know of a device that will take a 1PPS GPS timing signal and 
> generate a 32.768 kHz sine wave output ?
> I have big digital clock that uses an 8 bit micro processor and an external 
> 32.768 crystal. Obviously the external crystal is
> awful for accuracy.
> 
> I have searched every where using as many search terms as I can think of and 
> can’t believe there is not a device that performs
> this function.
> 
> I have found a couple of Epson RTC chips that might come close that 1pps but 
> I don’t think that corrects the 32khz just the clock time.
> 
> 2. 10 Mhz Freq Standard
> I am not in the same league as the majority of the list members and just 
> starting to dabble in GPSDO stuff.
> I have tried to find a thunderbolt as a starting device but it appears those 
> are either dried up or people want too much money.
> 
> I wanted to get the opinion of anyone who has tried the Leo Bodnar GPSDO ?
> For the money it appears to offer a beginner a lot of features.
> 
> Thanks and reading the daily digest of what you guys are working on.
> I have a feeling if I am not careful you guys could cost me a lot of money. 
> hehe
> 
> 
> Lee
> 
> 
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Re: [time-nuts] 1PPS to 32.768 khz

[Tom Van Baak]

Hi Brooke,

> So why not bypass the 32768 and drive the clock directly from the 1 PPS you 
> now have.

Right, but that trick only works with analog stepper motor clocks. OP has a 
"big digital clock" with 8-bit cpu and 32 kHz xtal. He didn't mention the 
make/model of digital clock but in my experience very few commodity clocks 
actually accept a 1PPS input. These clocks use 32 kHz:

1) to drive the MCU which computes day / date / hh:mm:ss, or manages alarms
2) to maintain timekeeping
3) to multiplex digits of the LED / LCD display (e.g., at 128 to 1024 Hz)
4) to create the short bipolar stepper motor pulse (e.g., 1/32 kHz * 512 = 1/64 
s = 15.6 ms).
5) to create the sound for the alarm/buzzer (some PWM based on 32 kHz)

The problem is that all these functions are usually integrated into one chip or 
even raw die/epoxy as in COB (Chip On Board). When hacking these sort of clocks 
it is often impossible to separate 32 kHz frequency features from the 1 Hz 
timing feature.

So when your goal is to improve timekeeping accuracy in these self-contained 
digital clocks it's usually easier and less invasive to make the clock use your 
precise 32 kHz signal instead of its own cheap xtal. You almost always have 
access to the xtal, but rarely access inside the MCU.

Note that you don't even need to unsolder the xtal -- you can "jam" the 
existing signal with an external 32 kHz sine or square wave applied to the XI 
pin (xtal in) of the MCU. Your external GPSDO/32kHz signal will "pull" the 
cheap xtal for free. Best yet, if your external signal goes away the clock 
keeps running using its own xtal without skipping a beat, like getting 
hold-over for free.

For a "no solder" or "no wires" solution, I have also tried to acoustically 
discipline a tuning fork xtal with an GPS-based 32 kHz signal and ultrasonic 
transducer. Poor results. I think I needed better coupling between the 
transducer and the xtal tuning fork. But in theory it should work. Plus it 
would keep small mammals and insects away from your clock.

/tvb

- Original Message - 
From: "Brooke Clarke" 
To: "Lee - N2LEE" ; "Discussion of precise time and frequency 
measurement" 
Sent: Wednesday, October 19, 2016 12:18 PM
Subject: Re: [time-nuts] 1PPS to 32.768 khz


Hi Lee:

32768 can easily be divided down to drive the clock.  So why not bypass the 
32768 and drive the clock directly from the 
1 PPS you now have.
http://www.prc68.com/I/QuartzClk.shtml

-- 
Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
The lesser of evils is still evil.

 Original Message 
> First let me say this is first time I have posted to the group so go easy on 
> me. :)
> Secondly I want everyone to know that you guys make me feel so NORMAL for
> wanting to use and understand accurate timing devices.
>
> I thought there was something seriously wrong with me now I know there are 
> others
> affected with the same disease. hehe
>
> Now my questions.
>
> 1. Does anyone know of a device that will take a 1PPS GPS timing signal and 
> generate a 32.768 kHz sine wave output ?
> I have big digital clock that uses an 8 bit micro processor and an external 
> 32.768 crystal. Obviously the external crystal is
> awful for accuracy.
>
> I have searched every where using as many search terms as I can think of and 
> can’t believe there is not a device that performs
> this function.
>
> I have found a couple of Epson RTC chips that might come close that 1pps but 
> I don’t think that corrects the 32khz just the clock time.
>
> 2. 10 Mhz Freq Standard
> I am not in the same league as the majority of the list members and just 
> starting to dabble in GPSDO stuff.
> I have tried to find a thunderbolt as a starting device but it appears those 
> are either dried up or people want too much money.
>
> I wanted to get the opinion of anyone who has tried the Leo Bodnar GPSDO ?
> For the money it appears to offer a beginner a lot of features.
>
> Thanks and reading the daily digest of what you guys are working on.
> I have a feeling if I am not careful you guys could cost me a lot of money. 
> hehe
>
>
> Lee

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Re: [time-nuts] 1PPS to 32.768 khz

[Brooke Clarke]

Hi Lee:

32768 can easily be divided down to drive the clock.  So why not bypass the 32768 and drive the clock directly from the 
1 PPS you now have.

http://www.prc68.com/I/QuartzClk.shtml

--
Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
The lesser of evils is still evil.

 Original Message 

First let me say this is first time I have posted to the group so go easy on 
me. :)
Secondly I want everyone to know that you guys make me feel so NORMAL for
wanting to use and understand accurate timing devices.

I thought there was something seriously wrong with me now I know there are 
others
affected with the same disease. hehe

Now my questions.

1. Does anyone know of a device that will take a 1PPS GPS timing signal and 
generate a 32.768 kHz sine wave output ?
I have big digital clock that uses an 8 bit micro processor and an external 
32.768 crystal. Obviously the external crystal is
awful for accuracy.

I have searched every where using as many search terms as I can think of and 
can’t believe there is not a device that performs
this function.

I have found a couple of Epson RTC chips that might come close that 1pps but I 
don’t think that corrects the 32khz just the clock time.

2. 10 Mhz Freq Standard
I am not in the same league as the majority of the list members and just 
starting to dabble in GPSDO stuff.
I have tried to find a thunderbolt as a starting device but it appears those 
are either dried up or people want too much money.

I wanted to get the opinion of anyone who has tried the Leo Bodnar GPSDO ?
For the money it appears to offer a beginner a lot of features.

Thanks and reading the daily digest of what you guys are working on.
I have a feeling if I am not careful you guys could cost me a lot of money. hehe


Lee


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Re: [time-nuts] 1PPS to 32.768 khz

[Chris Albertson]

Even if the micro controller had to directly control the LEDs on the clock
your suggestion would be not only simpler bot several orders of magnitude
more accurate.I'd guess that a first attempt to build a 32KHz GPSDO
would not be perfect but the PPS signal is effectively dead-in perfect in
this use case.

The disadvantage of using there GPS directly to increment the clock is you
loose hold over.  The clock stops when GPS goes away.

A GPSDO has a "flywheel effect" and can continue to run on it's own if the
GPS is interrupted.  When the GPS signal returns it can slowly recover.
But do you care?

One other unleaded idea, can you control the frequency of a 32K crystal by
controlling its temperature?   If you can then that might be easier then
using a diode tuner.   It is easy t build a heater, epoxy a resistor to the
crystal.

On Wed, Oct 19, 2016 at 6:15 AM, Dave Martindale 
wrote:

> If the "big digital clock" doesn't display the time with fractional-second
> precision, then it only needs to be updated at 1 Hz, which can be done with
> the 1 PPS directly.  Consider replacing the 32 kHz crystal, divider chain,
> and microprocessor with a new microcontroller that takes 1 Hz input and
> drives the display in the same way.
>
> For an extra bonus, use a microcontroller with a serial port, and connect
> the GPS receiver serial output to the serial port on the micro.  Then you
> can decode the serial data stream from the GPS, and automatically set the
> clock to the correct time after a power failure - something the original
> clock could not do.  As a double bonus, make the clock display leap seconds
> correctly when they happen.
>
-- 

Chris Albertson
Redondo Beach, California
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Re: [time-nuts] 1PPS to 32.768 khz

[Chris Albertson]

On Wed, Oct 19, 2016 at 6:15 AM, Dave Martindale 
wrote:

> If the "big digital clock" doesn't display the time with fractional-second
> precision, then it only needs to be updated at 1 Hz, which can be done with
> the 1 PPS directly.  Consider replacing the 32 kHz crystal, divider chain,
> and microprocessor with a new microcontroller that takes 1 Hz input and
> drives the display in the same way.
>
> For an extra bonus, use a microcontroller with a serial port, and connect
> the GPS receiver serial output to the serial port on the micro.  Then you
> can decode the serial data stream from the GPS, and automatically set the
> clock to the correct time after a power failure - something the original
> clock could not do.  As a double bonus, make the clock display leap seconds
> correctly when they happen.
>
> - Dave
>
> On Tue, Oct 18, 2016 at 10:03 PM, Lee - N2LEE via time-nuts <
> time-nuts@febo.com> wrote:
>
> >
> > 1. Does anyone know of a device that will take a 1PPS GPS timing signal
> > and generate a 32.768 kHz sine wave output ?
> > I have big digital clock that uses an 8 bit micro processor and an
> > external 32.768 crystal. Obviously the external crystal is
> > awful for accuracy.
> >
> >
> >
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>



-- 

Chris Albertson
Redondo Beach, California
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Re: [time-nuts] 1PPS to 32.768 khz

[Tom Van Baak]

David, Hal,

When I did the PIC divider I first tried the normal phase accumulator (DDS) 
approach. But I couldn't fit it in 38 instructions. So that's why I went with 
the binary leap year-like approach instead. The code, and very detailed 
comments are at:
http://www.leapsecond.com/pic/src/pd30.asm

Note this chip, like most of my PIC dividers, is drop-in compatible with the 
TAPR TADD-2 mini board:
https://www.tapr.org/kits_t2-mini.html

/tvb


- Original Message - 
From: "Hal Murray" 
To: "Discussion of precise time and frequency measurement" 
Cc: 
Sent: Wednesday, October 19, 2016 3:29 AM
Subject: Re: [time-nuts] 1PPS to 32.768 khz


> 
> davidwh...@gmail.com said:
>> I think a PIC might be fast enough to DDS it.  The output bandpass filter
>> will cure a lot of sin.  Using a dedicated switched capacitor filter would
>> be fun but more expensive. 
> 
> There are two parts to a DDS like setup.  One is the math for the DDS and 
> then spining for the right number of cycles.  The other is a PLL to measure 
> the speed of the clock driving the CPU and tweaking the DDS "constants" so it 
> tracks the PPS.  It might be fun to do that with a fixed number of cycles.  
> Or maybe you can use a counter/timer to count cycles.
> 
> You don't need any filtering.  The goal is not to make a pretty picture on a 
> spectrum analyzer.  All you have to do is get the long term timing right so 
> the clock doesn't drift.
> 
> -- 
> These are my opinions.  I hate spam.
> 

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Re: [time-nuts] 1PPS to 32.768 khz

[Lee - N2LEE via time-nuts]

You guys are great. I especially like the more creative solutions that could 
take this project to a different level.

I should have known that my request was not a simple one. :)

While going from 1 PPS to 32.786 is not as easy as I had hoped what I find odd 
is that others must have been
looking for this same solution. Hard to believe an innovative chip designer has 
not solved this problem.

I have been able to find solutions that come close.
For example Epson /Seiko makes a RTC chip with a built in TCXO that will let 
you use the devices 32khz oscillator and
it allows for 1 PPS input. BUT (always a but) I don't think it corrects the 
oscillator just the RTC clock. (I think).

http://www5.epsondevice.com/en/products/i2c/rx8803sa.html

I have to tell you guys the recommendations I am getting are great even if they 
don't solve my exact solution.
The reason is you are giving me a lot to think about and research which means I 
am learning. I LOVE That ! :)

Keep the ideas coming and thanks for your patience.

Lee




On Oct 19, 2016, at 9:15 AM, Dave Martindale  wrote:

> If the "big digital clock" doesn't display the time with fractional-second 
> precision, then it only needs to be updated at 1 Hz, which can be done with 
> the 1 PPS directly.  Consider replacing the 32 kHz crystal, divider chain, 
> and microprocessor with a new microcontroller that takes 1 Hz input and 
> drives the display in the same way.
> 
> For an extra bonus, use a microcontroller with a serial port, and connect the 
> GPS receiver serial output to the serial port on the micro.  Then you can 
> decode the serial data stream from the GPS, and automatically set the clock 
> to the correct time after a power failure - something the original clock 
> could not do.  As a double bonus, make the clock display leap seconds 
> correctly when they happen.
> 
> - Dave
> 
> On Tue, Oct 18, 2016 at 10:03 PM, Lee - N2LEE via time-nuts 
>  wrote:
> 
> 1. Does anyone know of a device that will take a 1PPS GPS timing signal and 
> generate a 32.768 kHz sine wave output ?
> I have big digital clock that uses an 8 bit micro processor and an external 
> 32.768 crystal. Obviously the external crystal is
> awful for accuracy.
> 
> 

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Re: [time-nuts] PC clock generator without 14.318MHz

[Vladimir Smotlacha]

On 10/18/2016 11:23 PM, Mike Cook wrote:



Le 18 oct. 2016 à 16:53, Vladimir Smotlacha  a écrit :



Hello,

I have operated own NTP servers with stable system clock for many years. The 
principle is quite simple - I replaced 14.318 MHz quartz with OCXO based 
circuit. Now I have to build few more servers with modern mini-ITX 
motherboards, however on many of them (e.g. from ASUS) I can’t find any 14.317 
MHz quartz.  Such frequency is a relic of original PC design and I wonder if it 
is used any other basic frequency in recent clock generators?


The 14.317MHz xtal was connected to the south bridge controller chip, but for 
recent CPUs this has gone away as has northbridge and the system clock has been 
integrated into the PCH (Platform Controller Hub) chip according to Wikipedia, 
so I suspect that if you find the clock feeding that , then you could stabilize 
it in that same way.



Thank you Mike, PCH will be object of my experiments.
I wonder than probably nobody solved stable clock source in "post 
14.318" mainboards.


Vladimir



thanks,
Vladimir
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"The power of accurate observation is commonly called cynicism by those who 
have not got it. »
George Bernard Shaw

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Re: [time-nuts] 1PPS to 32.768 khz

[Dan Kemppainen]

Hi,

=
If you want to go Tom's picDIV route, and are lazy like me, this is one 
of several boards available.


https://oshpark.com/shared_projects/kXG6K5Xu

You'll get several copies of the bard board for under $10. Few minutes 
stuffing it, and you'll have a working device...


Dan




Hi Lee,

It's not likely you can directly multiply 1PPS up to 32 kHz, but it's easy to 
divide 10 MHz down to 32 kHz.
See http://leapsecond.com/pic/src/pd30.asm for a $1 PIC example.

A stand-alone 10 MHz OCXO or the simplest possible GPSDO would work for your 
digital clock project. Chris and Nick and many others have shared low-cost 
Arduino-class examples to the list over the years. Another example is the 
MCU-less James Miller design which uses a PLL at 10 kHz.

Contact me off-list some day when want a Trimble Thunderbolt; they are still 
available.

/tvb

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Re: [time-nuts] 1PPS to 32.768 khz

[Cube Central]

Lee,

Welcome to the list!   I happen to have just installed a Leo Bodnar GPSDO and 
it is running currently here.  It is a *very* nice unit, well thought out, and 
nicely put together.  The price is a bit steep for an entry level device, 
however I feel it is work it.

Another wonderful unit can be found here: 
https://www.tindie.com/products/nsayer/gps-disciplined-xcxo/
I also have this unit and it is the 10MHz standard on my workbench.  Another 
quality product, it is well designed and put together.

You can't go wrong with either of these units.  The LeoNTP is more for serving 
ntp to clients, the Nick Sayer one more for a frequency standard.

Cheers!

-Randal R.
(at CubeCentral)



-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Lee - N2LEE 
via time-nuts
Sent: Tuesday, 18 October, 2016 20:03
To: time-nuts@febo.com
Subject: [time-nuts] 1PPS to 32.768 khz

First let me say this is first time I have posted to the group so go easy on 
me. :) Secondly I want everyone to know that you guys make me feel so NORMAL 
for wanting to use and understand accurate timing devices.

I thought there was something seriously wrong with me now I know there are 
others affected with the same disease. hehe

Now my questions.

1. Does anyone know of a device that will take a 1PPS GPS timing signal and 
generate a 32.768 kHz sine wave output ?
I have big digital clock that uses an 8 bit micro processor and an external 
32.768 crystal. Obviously the external crystal is awful for accuracy.

I have searched every where using as many search terms as I can think of and 
can’t believe there is not a device that performs this function.

I have found a couple of Epson RTC chips that might come close that 1pps but I 
don’t think that corrects the 32khz just the clock time.

2. 10 Mhz Freq Standard
I am not in the same league as the majority of the list members and just 
starting to dabble in GPSDO stuff.
I have tried to find a thunderbolt as a starting device but it appears those 
are either dried up or people want too much money.

I wanted to get the opinion of anyone who has tried the Leo Bodnar GPSDO ?
For the money it appears to offer a beginner a lot of features.

Thanks and reading the daily digest of what you guys are working on.
I have a feeling if I am not careful you guys could cost me a lot of money. hehe


Lee


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Re: [time-nuts] 1PPS to 32.768 khz

[Dave Martindale]

If the "big digital clock" doesn't display the time with fractional-second
precision, then it only needs to be updated at 1 Hz, which can be done with
the 1 PPS directly.  Consider replacing the 32 kHz crystal, divider chain,
and microprocessor with a new microcontroller that takes 1 Hz input and
drives the display in the same way.

For an extra bonus, use a microcontroller with a serial port, and connect
the GPS receiver serial output to the serial port on the micro.  Then you
can decode the serial data stream from the GPS, and automatically set the
clock to the correct time after a power failure - something the original
clock could not do.  As a double bonus, make the clock display leap seconds
correctly when they happen.

- Dave

On Tue, Oct 18, 2016 at 10:03 PM, Lee - N2LEE via time-nuts <
time-nuts@febo.com> wrote:

>
> 1. Does anyone know of a device that will take a 1PPS GPS timing signal
> and generate a 32.768 kHz sine wave output ?
> I have big digital clock that uses an 8 bit micro processor and an
> external 32.768 crystal. Obviously the external crystal is
> awful for accuracy.
>
>
>
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Re: [time-nuts] 1PPS to 32.768 khz

[planophore]

Lee,

Another option might be something like this:

http://qrp-labs.com/progrock.html

it is a standalone ATTiny based device which uses a plug in Si5351a
synthesizer. Output frequencies from as low as 3.515 khz to a 100+ MHz
can programmed and can be GPS disciplined suing a GPS' PPS. There are
some limits on the PPS (i.e. very narrow will work).

Granted, phase noise and jitter in this example are a wildcard and I
couldn't comment on that with respect to your application.

The Si5351a synthesizer board uses a simple 27MHz crystal but can
replaced with a standard SMD 27MHz oscillator or TCXO. Once "burned"
in, can be very stable all on it's own and may be sufficient your needs.

cheers, Graham

On 10/19/2016, "Lee - N2LEE via time-nuts"  wrote:

>First let me say this is first time I have posted to the group so go easy on 
>me. :)
>Secondly I want everyone to know that you guys make me feel so NORMAL for
>wanting to use and understand accurate timing devices.
>
>I thought there was something seriously wrong with me now I know there are 
>others
>affected with the same disease. hehe
>
>Now my questions.
>
>1. Does anyone know of a device that will take a 1PPS GPS timing signal and 
>generate a 32.768 kHz sine wave output ?
>I have big digital clock that uses an 8 bit micro processor and an external 
>32.768 crystal. Obviously the external crystal is
>awful for accuracy.
>
>I have searched every where using as many search terms as I can think of and 
>can’t believe there is not a device that performs
>this function.
>
>I have found a couple of Epson RTC chips that might come close that 1pps but I 
>don’t think that corrects the 32khz just the clock time.
>
>2. 10 Mhz Freq Standard
>I am not in the same league as the majority of the list members and just 
>starting to dabble in GPSDO stuff.
>I have tried to find a thunderbolt as a starting device but it appears those 
>are either dried up or people want too much money.
>
>I wanted to get the opinion of anyone who has tried the Leo Bodnar GPSDO ?
>For the money it appears to offer a beginner a lot of features.
>
>Thanks and reading the daily digest of what you guys are working on.
>I have a feeling if I am not careful you guys could cost me a lot of money. 
>hehe
>
>
>Lee
>
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Re: [time-nuts] 1PPS to 32.768 khz

[Hal Murray]

davidwh...@gmail.com said:
> I think a PIC might be fast enough to DDS it.  The output bandpass filter
> will cure a lot of sin.  Using a dedicated switched capacitor filter would
> be fun but more expensive. 

There are two parts to a DDS like setup.  One is the math for the DDS and 
then spining for the right number of cycles.  The other is a PLL to measure 
the speed of the clock driving the CPU and tweaking the DDS "constants" so it 
tracks the PPS.  It might be fun to do that with a fixed number of cycles.  
Or maybe you can use a counter/timer to count cycles.

You don't need any filtering.  The goal is not to make a pretty picture on a 
spectrum analyzer.  All you have to do is get the long term timing right so 
the clock doesn't drift.

-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] 1PPS to 32.768 khz

[David J Taylor]

First let me say this is first time I have posted to the group so go easy on 
me. :)

Secondly I want everyone to know that you guys make me feel so NORMAL for
wanting to use and understand accurate timing devices.

I thought there was something seriously wrong with me now I know there are 
others

affected with the same disease. hehe

Now my questions.
[]
2. 10 Mhz Freq Standard
[]
I wanted to get the opinion of anyone who has tried the Leo Bodnar GPSDO ?
For the money it appears to offer a beginner a lot of features.

Thanks and reading the daily digest of what you guys are working on.
I have a feeling if I am not careful you guys could cost me a lot of money. 
hehe


Lee
==

Lee,

I have one of the Leo Bodnar GPSDO devices and it works well, using a patch 
antenna on the top floor of a building.  I haven't subjected it to detailed 
measurements but others here have.  You can use it to drive some SDR devices 
too, such as the AirSpy.  Being a new device, it's fully supported, of 
course, and it has two outputs (linked in frequency).


73,
David GM8ARV
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-tay...@blueyonder.co.uk
Twitter: @gm8arv 


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Re: [time-nuts] 1PPS to 32.768 khz

[Dave Brown]

Lee
Might be easier to run the GPSDO up at 16,384 kHz, like the E1 area telcos 
used to do (and some still do)- then divide that by 500 when your done with 
the PLL side of things and you have a clean stable 32.768 kHz reference to 
feed into the micro in place of the xtal.
But first off, I'd be inclined to dig into the micro circuitry in the clock 
and see if and where you might be able to feed in the 1 PPS  instead of that 
derived from the 32 kHz xtal.

DaveB, NZ

- Original Message - 
From: "Chris Albertson" 
To: "Lee - N2LEE" ; "Discussion of precise time and frequency 
measurement" 

Sent: Wednesday, October 19, 2016 7:26 PM
Subject: Re: [time-nuts] 1PPS to 32.768 khz



What you want is a GPSDO.  Most people here build these to run at 10MHz.
But you need one that runs at 32768 kHz.

Try this:  Divide the crystal oscillator's output by 32768.  This will 
give
you one Hz.   Compare the phase of this with the phase of your PPS from 
the

GPS.  Push and pull the crystal oscillator so that the phase is locked.

The first and most critical step is to build a good 32768 Hz oscillator
that can be fine tuned by a controlling voltage.   Usually a reverse 
biased

diode is used because the capacitance of the diode depends on the voltage
across it. You'll need a very good quality 32768 Hz voltage controlled
oscillator (VCO).

In short, go the other way around, don't try and scale up the 1PPS, scale
the 32K down to 1Hz

That said, y you really don't have to divide the 32K signal.   Measure the
time from the zero crossing of the PPS to the nest zero crossing of the 
32K

signal and control the VCO to keep this time constant.   What you are
building isa phase locked loop



Now my questions.


1. Does anyone know of a device that will take a 1PPS GPS timing signal
and generate a 32.768 kHz sine wave output ?
I have big digital clock that uses an 8 bit micro processor and an
external 32.768 crystal. Obviously the external crystal is
awful for accuracy.

I have searched every where using as many search terms as I can think of
and can’t believe there is not a device that performs
this function.

I have found a couple of Epson RTC chips that might come close that 1pps
but I don’t think that corrects the 32khz just the clock time.

2. 10 Mhz Freq Standard
I am not in the same league as the majority of the list members and just
starting to dabble in GPSDO stuff.
I have tried to find a thunderbolt as a starting device but it appears
those are either dried up or people want too much money.

I wanted to get the opinion of anyone who has tried the Leo Bodnar GPSDO 
?

For the money it appears to offer a beginner a lot of features.

Thanks and reading the daily digest of what you guys are working on.
I have a feeling if I am not careful you guys could cost me a lot of
money. hehe


Lee


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Chris Albertson
Redondo Beach, California
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Re: [time-nuts] 1PPS to 32.768 khz

[David]

On Tue, 18 Oct 2016 22:59:42 -0700, you wrote:

>> 1. Does anyone know of a device that will take a 1PPS GPS timing signal and
>> generate a 32.768 kHz sine wave output ? I have big digital clock that uses
>> an 8 bit micro processor and an external 32.768 crystal. Obviously the
>> external crystal is awful for accuracy. 
>
>I don't know of any off-the-shelf device that does that.

I do not either which I found surprising.  I did a search back through
the archives and found lots of posts about synthesizing 32.768kHz from
10 MHz but nothing about 1 PPS.

>Have you looked at the micro?  Is there a spare input pin for the PPS?  Could 
>you rewrite the software to use the PPS rather than counting to 32K?
>
>If you get a GPSDO with a 10 MHz output, then you could do it in software.  
>I'm a bit surprised that tvb doesn't already have one as an option for his 
>picDEVs.
>  http://www.leapsecond.com/pic/picdiv.htm

Lots of discussion about this in the archives.

>If you think (analog) hardware is more fun than software, you could build a 
>PLL.  I'm not a PLL wizard.  My guess is that 32K:1 is too big a step.  I'd 
>probably try 2 steps of 256:1 and 128:1.

It is not nearly that complicated.  I would almost call it trivial.
Phase performance is not critical in this application as long as
cycles are not added or lost.

Phase lock a 32.768kHz crystal oscillator to the PPS output either
directly or after dividing it down by a couple powers of 2 to remove
any ambiguity.  Several of the 10 MHz analog GPSDOs work this way. The
time constant just has to be long enough for the required holdover.

How much tuning range does a varactor tuned 32.768kHz crystal
oscillator have?  I knew at one time.

>If you like software, you can do the PLL in software.  (Less hardware than 
>the analog version.)  The idea is to run a tiny CPU at some handy frequency, 
>measure that clock using the PPS, and figure out how many cycles you need for 
>each half cycle at 32K Hz.  You don't need each (half) cycle to be super 
>accurate, but the long term has to be right.  If you knew the clock frequency 
>and it was stable, the cycles-per-tick would turn into the same sort of math 
>at Bresenham's algorithm gets for drawing diagonal lines:  some steps are N 
>cycles, some are N+1.  I'll bet the code is nice and clean after you figure 
>out how to do it.  Maybe it's just a PLL in software.

I think a PIC might be fast enough to DDS it.  The output bandpass
filter will cure a lot of sin.  Using a dedicated switched capacitor
filter would be fun but more expensive.
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Re: [time-nuts] 1PPS to 32.768 khz

[Chris Albertson]

What you want is a GPSDO.  Most people here build these to run at 10MHz.
But you need one that runs at 32768 kHz.

Try this:  Divide the crystal oscillator's output by 32768.  This will give
you one Hz.   Compare the phase of this with the phase of your PPS from the
GPS.  Push and pull the crystal oscillator so that the phase is locked.

The first and most critical step is to build a good 32768 Hz oscillator
that can be fine tuned by a controlling voltage.   Usually a reverse biased
diode is used because the capacitance of the diode depends on the voltage
across it. You'll need a very good quality 32768 Hz voltage controlled
oscillator (VCO).

In short, go the other way around, don't try and scale up the 1PPS, scale
the 32K down to 1Hz

That said, y you really don't have to divide the 32K signal.   Measure the
time from the zero crossing of the PPS to the nest zero crossing of the 32K
signal and control the VCO to keep this time constant.   What you are
building isa phase locked loop



Now my questions.
>
> 1. Does anyone know of a device that will take a 1PPS GPS timing signal
> and generate a 32.768 kHz sine wave output ?
> I have big digital clock that uses an 8 bit micro processor and an
> external 32.768 crystal. Obviously the external crystal is
> awful for accuracy.
>
> I have searched every where using as many search terms as I can think of
> and can’t believe there is not a device that performs
> this function.
>
> I have found a couple of Epson RTC chips that might come close that 1pps
> but I don’t think that corrects the 32khz just the clock time.
>
> 2. 10 Mhz Freq Standard
> I am not in the same league as the majority of the list members and just
> starting to dabble in GPSDO stuff.
> I have tried to find a thunderbolt as a starting device but it appears
> those are either dried up or people want too much money.
>
> I wanted to get the opinion of anyone who has tried the Leo Bodnar GPSDO ?
> For the money it appears to offer a beginner a lot of features.
>
> Thanks and reading the daily digest of what you guys are working on.
> I have a feeling if I am not careful you guys could cost me a lot of
> money. hehe
>
>
> Lee
>
>
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/
> mailman/listinfo/time-nuts
> and follow the instructions there.
>



-- 

Chris Albertson
Redondo Beach, California
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Re: [time-nuts] 1PPS to 32.768 khz

[Hal Murray]

> 1. Does anyone know of a device that will take a 1PPS GPS timing signal and
> generate a 32.768 kHz sine wave output ? I have big digital clock that uses
> an 8 bit micro processor and an external 32.768 crystal. Obviously the
> external crystal is awful for accuracy. 

I don't know of any off-the-shelf device that does that.

Have you looked at the micro?  Is there a spare input pin for the PPS?  Could 
you rewrite the software to use the PPS rather than counting to 32K?

If you get a GPSDO with a 10 MHz output, then you could do it in software.  
I'm a bit surprised that tvb doesn't already have one as an option for his 
picDEVs.
  http://www.leapsecond.com/pic/picdiv.htm

If you think (analog) hardware is more fun than software, you could build a 
PLL.  I'm not a PLL wizard.  My guess is that 32K:1 is too big a step.  I'd 
probably try 2 steps of 256:1 and 128:1.

If you like software, you can do the PLL in software.  (Less hardware than 
the analog version.)  The idea is to run a tiny CPU at some handy frequency, 
measure that clock using the PPS, and figure out how many cycles you need for 
each half cycle at 32K Hz.  You don't need each (half) cycle to be super 
accurate, but the long term has to be right.  If you knew the clock frequency 
and it was stable, the cycles-per-tick would turn into the same sort of math 
at Bresenham's algorithm gets for drawing diagonal lines:  some steps are N 
cycles, some are N+1.  I'll bet the code is nice and clean after you figure 
out how to do it.  Maybe it's just a PLL in software.


-- 
These are my opinions.  I hate spam.



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