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

[Scott Stobbe]

If the heart of your clock is a micro, you may be able to reset the
processor and set the time once a second fastest enough not to have any
visual artifacts. Even if you have a perfect 32.768 kHz clock you still
have to set the phase (time) manually and deal with DST, leap seconds,
and power failures if your total setup doesn't have battery backup.

On Wednesday, 19 October 2016, Lee - N2LEE via time-nuts 
wrote:

> 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

[Tom Van Baak]

Hi Jim,

I'm glad you mentioned the DS3231 aging trick. Many PIC's also have the ability 
to digitally tune their internal low power oscillator. Attached is a plot 
showing the 32 steps of the OSCTUNE register in a $1 8-pin PIC12F683.

Notice in the plot that the frequency adjustment range (and step size) of the 
PIC tuning is very large (+/- 10% fs) compared to the DS3231 (0.1ppm/lsb). This 
is both good and bad, depending on your application.

One trick that I've used is to apply PWM to the 7-bit OSCTUNE register. 
Although most people set the value once and forget it, there's no rule that 
says you can't update the register periodically, even rapidly. So for improved 
frequency resolution I update OSCTUNE every millisecond (!) as one would with 
PWM.

Using 1% PWM resolution, the 32 coarse OSCTUNE steps now turn into 3200 fine 
frequency tunings. With additional effort a GPS/1PPS pin capture directs the 
step size/direction and you can thus eliminate both the DS3231 and the Arduino. 
It's my $1 "best worst GPSDO" project. For you PIC assembly programmers the 
frequency microstep test code is at http://leapsecond.com/pic/src/pg41.asm

The key realization is that many microcontrollers now have internal 
oscillators, programmable oscillator tuning, and pulse capture capability. So 
they can function as a crude 1-chip GPSDO. Still, from a practical standpoint, 
the two chip DS3231 + PIC/AVR/Arduino is a more robust and stable solution, 
especially in the case where the goal is 32 kHz output.

/tvb

- Original Message - 
From: "Jim Harman" <j99har...@gmail.com>
To: "Discussion of precise time and frequency measurement" <time-nuts@febo.com>
Sent: Friday, October 21, 2016 10:42 AM
Subject: Re: [time-nuts] 1PPS to 32.768 khz


> On Thu, Oct 20, 2016 at 7:08 AM, Bob Camp <kb...@n1k.org> wrote:
> 
>> One problem with a PLL and a 1 Hz input are the values of components
>> you get in the loop.
>> The other issue is the cost of the VCXO that will get
>> you to 32,768 KHz.
>>
> 
> As I mentioned earlier, the DS3231 chip (about $6.50 qty 1 or $17.50 on a
> breakout board) might be a reasonable approach for this. It is a
> self-contained 32.768 KHz TCXO that lets you vary the frequency in steps of
> 0.1 ppm using its I2C interface. Left to its own devices, it measures the
> ambient temperature and switches its on-chip capacitors in and out to
> control its frequency.
> 
> It has both 1 PPS and 32,768 Hz outputs. Connected to an Arduino-class
> processor, you could measure the time delay between its PPS and the PPS
> from a GPS and tweak the oscillator accordingly, making a complete 32.768
> KHz GPSDO including the GPS with just 3 chips.
> 
> And you get RTC functionality and battery backup circuitry thrown in for
> free.
> 
> 
> -- 
> 
> --Jim Harman
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Re: [time-nuts] 1PPS to 32.768 khz

[ed breya]

I'm kind of late to the party on this one, but I think the simplest 
approach with the least disturbance to the operation of the original 
system would be to form a VCXO and PLL.


Good old 4000 series CMOS stuff should be plenty fast enough. Two pieces 
should be sufficient. For example, a CMOS 4060 counter/oscillator plus a 
32,768 Hz resonator, rigged as a VCXO could make the clock, and also 
divide it down to a convenient range for 1 PPS comparison. A 4046 PLL or 
some simple logic could then do the comparison and make the correction 
voltage to the oscillator.


Another option may be to use the clock chip's own system to get a 
comparison frequency, if there is a definite and fixed relationship to 
some output signal, say a digit scan line, or punctuation (colons 
between HMS) flash signal. It's conceivable to then use the chip's XO, 
modified to make it voltage-tuned, along with some form of phase 
detector logic.


This could be very simple to implement, but would take some figuring 
out, and risks hurting the clock chip if you screw up while 
experimenting - a definite disturbance. So, it's probably best to use an 
external circuit for all.


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

[Jim Harman]

On Thu, Oct 20, 2016 at 7:08 AM, Bob Camp  wrote:

> One problem with a PLL and a 1 Hz input are the values of components
> you get in the loop.
> The other issue is the cost of the VCXO that will get
> you to 32,768 KHz.
>

As I mentioned earlier, the DS3231 chip (about $6.50 qty 1 or $17.50 on a
breakout board) might be a reasonable approach for this. It is a
self-contained 32.768 KHz TCXO that lets you vary the frequency in steps of
0.1 ppm using its I2C interface. Left to its own devices, it measures the
ambient temperature and switches its on-chip capacitors in and out to
control its frequency.

It has both 1 PPS and 32,768 Hz outputs. Connected to an Arduino-class
processor, you could measure the time delay between its PPS and the PPS
from a GPS and tweak the oscillator accordingly, making a complete 32.768
KHz GPSDO including the GPS with just 3 chips.

And you get RTC functionality and battery backup circuitry thrown in for
free.


-- 

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

[Chris Albertson]

On Wed, Oct 19, 2016 at 8:32 PM, Lee - N2LEE via time-nuts <
time-nuts@febo.com> wrote:

>
> 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.
>

Can you point all of those POE NTP clocks to a common LOCAL NTP server?
Time will be within a couple tens of milliseconds they will be in sync well
enough that the eye can not notice.But this means setting up a local
NTP server.   Any spare computer can do this you can connect a GPS if you
like but will not help much in this use case

-- 

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

[Bob Camp]

Hi

One problem with a PLL and a 1 Hz input are the values of components
you get in the loop. The other issue is the cost of the VCXO that will get 
you to 32,768 KHz. The PLL as described by the OP would need the 1 pps
divided by 2 with a lot of PLL chips. You now are locking 32768 to 0.5 Hz. 

It gets complicated pretty fast.

Bob

> On Oct 19, 2016, at 11:07 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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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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> 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

[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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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 <t...@leapsecond.com> 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" <bro...@pacific.net>
> To: "Lee - N2LEE" <l...@n2lee.com>; "Discussion of precise time and
> frequency measurement" <time-nuts@febo.com>
> 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 mone

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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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" <bro...@pacific.net>
To: "Lee - N2LEE" <l...@n2lee.com>; "Discussion of precise time and frequency 
measurement" <time-nuts@febo.com>
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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> 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

[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" <hmur...@megapathdsl.net>
To: "Discussion of precise time and frequency measurement" <time-nuts@febo.com>
Cc: <hmur...@megapathdsl.net>
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] 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" <albertson.ch...@gmail.com>
To: "Lee - N2LEE" <l...@n2lee.com>; "Discussion of precise time and frequency 
measurement" <time-nuts@febo.com>

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

[Bill Hawkins]

Hi Lee,

We all had a first time posting on this list and survived it. No
problem.

You need to know more about phase locked loops. In this case, you need a
voltage controlled crystal oscillator that a simple binary divider can
take down to 1 PPS. That 1 PPS is compared to the GPS 1 PPS with a
simple flip-flop, which produces a pulse width that can be filtered to
be the control voltage for your VCXO. The resulting feedback loop causes
your VCXO to track GPS.

Now then, this is a great oversimplification of the process for getting
very low timing errors. However, human time constants for observation of
a clock do not require very low timing errors. Very few people would
notice a 50 millisecond error. 

To get a useful answer from this group, you need to specify the accuracy
required. If you want picosecond errors, you are into big bucks.
Nanosecond errors are expensive but can be found on eBay. Microsecond
errors still need a good GPS receiver (not cheap). Millisecond errors
are not normally the subject of this group, although there has been a
thread on receivers barely capable of that.

Lurk and learn, grasshopper. The cost is low until you decide on the
level of accuracy you wish to reach.

Best regards,
Bill Hawkins

P.S. I was afflicted with the desire for accuracy down to the Caesium
standard level. Hydrogen masers remained beyond my means. Now I live in
an apartment in an old folks community, which required severe
downsizing. The return on investment was negative. The older I get, the
less I require precision time. YMMV.


-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Lee -
N2LEE via time-nuts
Sent: Tuesday, October 18, 2016 9:03 PM
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

[Tom Van Baak]

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

- Original Message - 
From: "Lee - N2LEE via time-nuts" 
To: 
Sent: Tuesday, October 18, 2016 7:03 PM
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

[Jim Harman]

Hi Lee,

It's not exactly what you asked for, but for your clock you might give this
a try, or consider using the underlying DS3231 chip directly.

https://www.adafruit.com/product/255

It is basically a much more accurate and stable than usual 32KHz
oscillator, with a TCXO that you can actually tweak programatically with a
resolution of about 0.1 ppm.

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



-- 

--Jim Harman
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