Re: [time-nuts] accurate 60 hz reference chips/ckts

[Tom Van Baak]

I sent a note to Vlad off-list about the bug in the MCU code, but it's worth a 
reminder to the list as well since many of you are programmers and this arcane 
issue comes up every once in a while here and on the web.

The way to compute time differences of free-running binary time counters is 
subtraction. One line of code. There is no need to special case overflow / 
rollover / wraparound. It is the very nature of unsigned or 2's compliment 
signed binary arithmetic that subtraction is sufficient. So the bug-free code 
is just this:

 uwIC2Value2 = (HAL_TIM_ReadCapturedValue(htim, TIM_CHANNEL_1));
 uwDiffCapture = (uwIC2Value2 - prevtimer);
 prevtimer = uwIC2Value2;

If you'd like a simple example why this is correct and a demonstration of what 
the bug was, see:

http://leapsecond.com/tools/deltatim.c

/tvb

- Original Message - 
From: "Vlad" <t...@patoka.org>
To: "Jeremy Nichols" <jn6...@gmail.com>
Cc: "Discussion of precise time and frequency measurement" <time-nuts@febo.com>
Sent: Friday, December 15, 2017 9:41 AM
Subject: Re: [time-nuts] accurate 60 hz reference chips/ckts



My setup is pretty simple indeed. This is 9.830400MHZ OCXO which 
clocking MCU. Then it is Zero-Cross detector which connected to capture 
timer.
The MCU counting the intervals between of each zero-cross event and 
number of events occurred.

 if (htim->Instance == TIM5 && htim->Channel == 
HAL_TIM_ACTIVE_CHANNEL_1) {
 uwIC2Value2 = (HAL_TIM_ReadCapturedValue(htim, TIM_CHANNEL_1));
 if (uwIC2Value2 >= prevtimer) {
 uwDiffCapture = (uwIC2Value2 - prevtimer);
 } else {
 uwDiffCapture =((0x - prevtimer) + uwIC2Value2);
 }

 prevtimer = uwIC2Value2;

 // MAIN Time calculation
 if(++uwCapT > 59) {  // Every 60 cycles (60hz)
 if(++maintime.Seconds > 59) {
 maintime.Seconds = 0;
 if(++maintime.Minutes > 59) {
 maintime.Minutes = 0;
 if(++maintime.Hours > 23)
 maintime.Hours = 0;
 }
 }
 uwCapT = 0;
}

Once an hour the program prints its internal clock (MCU time), RTC time 
and MAIN time

# Uptime:   476 hours
# RTC time: 13:00:00
# MCU time: 13:00:00
# MAIN time:13:00:01

The graph shows the "delta" between of RTC and MAIN.


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Re: [time-nuts] accurate 60 hz reference chips/ckts

[Gary E. Miller]

Yo All!

Jeremy wrote:

> I'm surprised Vlad is seeing as much as six seconds differential
> but maybe I don't understand the experiment. I've done measurements
> of the line frequency here in California and never seen much
> variation.  

I live in Central Oregon.  Next to the Pacific Intertie and the Paccific
DC Intertie.  Near the Round Butte Dam, Pelton Dam, and other power
generating dams.

The Interties connect the massive hydropower generation of the Columbia
River system with southern California.

The hypropower system includes the best technology of the 1930's, 1940's
and 1950's.

I've had converstations with some of the dam operators about how
they keep frequency.  Pretty simple really.  Huge tonnages of spinning
steel and copper being pushed by falling water.  The water is regulated
by flapper valves.  Pretty stable short term.

Now imagine when a 300MVA intertie blows over, or is burned by a fire,
and instantly disconnects.  Or a steel mill shuts down for the day, or...

The electrical backpressure to the generators drops, so the generators
speed up, increasing the line frequency and voltage.

When this happens, the dam operators literally pick up the phone, and
talk to the other dams to decide what to do.  Usually that involves
one or more dams closing down a few flapper vavles.

That is how the short term frequency of your local power line is
controlled.

The control room also has a AC synchronous clock, off the power line, 
and an accurate digital clock.  Once a day they manually get the
AC clock to agree with the digital clocl.

None of this is rocket science, don't use it for anything you need
any accuracy for.

RGDS
GARY
---
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
g...@rellim.com  Tel:+1 541 382 8588

Veritas liberabit vos. -- Quid est veritas?
"If you can’t measure it, you can’t improve it." - Lord Kelvin


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Re: [time-nuts] accurate 60 hz reference chips/ckts

[Charles Steinmetz]

Jeremy wrote:


I'm surprised Vlad is seeing as much as six seconds differential but maybe
I don't understand the experiment. I've done measurements of the line
frequency here in California and never seen much variation.


When was the earliest time (year) you started looking seriously at the 
offset/frequency of your grid?  (California is part of the [North 
American] Western Interconnection.)


I have only closely observed the line frequency and offset when I have 
been living within the Eastern Interconnection.  For years and years 
between the 1960s and the 1980s, it was not unusual to observe offsets 
of +/- 30 seconds, and +/- 60 seconds was not unheard of.  I believe the 
policy has always been to provide 5.184e6 cycles per 24-hour day, so the 
+ and - offsets had to cancel over a specific 24 hour period.


I then didn't pay any attention to the mains frequency until the late 
aughties, and I found that things have changed.  Now, I rarely see 
offsets greater than +/- 4 to 6 seconds (very rarely, +/- 15 seconds) -- 
but it does not follow a gaussian distribution, to my (totally 
anecdotal) observation.  It appears to me (again, completely 
anecdotally) that it is more often within the lowest 25% or the highest 
25% [combined] than it is the middle 50%, indicating a process that is 
being controlled with a marginally stable loop.  (Of course, it *is* 
being controlled -- with a massively distributed feedback system.  So no 
surprise there.)


Best regards,

Charles


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Re: [time-nuts] accurate 60 hz reference chips/ckts

[Bob kb8tq]

Hi

It depends a *lot* on just where you are and how the “gird” is managed. Many 
years
ago, we figured out that the local power company corrected things between 4 and 
5 PM.
It became a habit to fire up WWV and watch them slip seconds one way or the 
other. A
ten second delta was not at all unusual. ( as in 10 seconds over the hour …). 
Our 
guess (later confirmed) was that they ran local generation part of the day 
(independent 
of the grid) and then went over to interconnect. 

Bob

> On Dec 15, 2017, at 12:14 PM, Jeremy Nichols  wrote:
> 
> I'm surprised Vlad is seeing as much as six seconds differential but maybe
> I don't understand the experiment. I've done measurements of the line
> frequency here in California and never seen much variation.
> 
> Jeremy
> 
> 
> On Fri, Dec 15, 2017 at 9:02 AM Vlad  wrote:
> 
>> 
>> 
>> I have one of my project boxes, which monitor the main freq. Here is
>> graph which reflect the time difference between of RTC (based on number
>> of pulses from OCXO) and the "MAIN TIME" which is based on number of
>> zero-cross events.
>> The observation period is 486 hours.
>> 
>> 
>> 
>> 
>> On 2017-12-14 23:13, Jim Harman wrote:
>>> On Thu, Dec 14, 2017 at 10:53 PM, Bob kb8tq  wrote:
>>> 
 
 
 Of course this *assumes* an electronic approach. Given that it’s
 moving
 pretty slow and you
 only are looking at fractions of a millisecond, one *could* do an
 electro
 mechanical design …...
 
 Bob
 
 There is interesting background on power grid frequency/time
 adjustment
>>> procedures here
>>> 
>> https://en.wikipedia.org/wiki/Utility_frequency#Time_error_correction_(TEC)
>>> 
>>> and here
>>> https://en.wikipedia.org/wiki/Electric_clock#Accuracy
>> 
>> --
>> WBW,
>> 
>> V.P.___
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> 
> -- 
> Sent from my iPad 4.
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Re: [time-nuts] accurate 60 hz reference chips/ckts

[Vlad]

My setup is pretty simple indeed. This is 9.830400MHZ OCXO which 
clocking MCU. Then it is Zero-Cross detector which connected to capture 
timer.
The MCU counting the intervals between of each zero-cross event and 
number of events occurred.


if (htim->Instance == TIM5 && htim->Channel == 
HAL_TIM_ACTIVE_CHANNEL_1) {

uwIC2Value2 = (HAL_TIM_ReadCapturedValue(htim, TIM_CHANNEL_1));
if (uwIC2Value2 >= prevtimer) {
uwDiffCapture = (uwIC2Value2 - prevtimer);
} else {
uwDiffCapture =((0x - prevtimer) + uwIC2Value2);
}

prevtimer = uwIC2Value2;

// MAIN Time calculation
if(++uwCapT > 59) {  // Every 60 cycles (60hz)
if(++maintime.Seconds > 59) {
maintime.Seconds = 0;
if(++maintime.Minutes > 59) {
maintime.Minutes = 0;
if(++maintime.Hours > 23)
maintime.Hours = 0;
}
}
uwCapT = 0;
   }

Once an hour the program prints its internal clock (MCU time), RTC time 
and MAIN time


# Uptime:   476 hours
# RTC time: 13:00:00
# MCU time: 13:00:00
# MAIN time:13:00:01

The graph shows the "delta" between of RTC and MAIN.

On 2017-12-15 12:14, Jeremy Nichols wrote:

I'm surprised Vlad is seeing as much as six seconds differential but
maybe I don't understand the experiment. I've done measurements of the
line frequency here in California and never seen much variation.

Jeremy

On Fri, Dec 15, 2017 at 9:02 AM Vlad  wrote:


I have one of my project boxes, which monitor the main freq. Here is
graph which reflect the time difference between of RTC (based on
number
of pulses from OCXO) and the "MAIN TIME" which is based on number of
zero-cross events.
The observation period is 486 hours.

On 2017-12-14 23:13, Jim Harman wrote:

On Thu, Dec 14, 2017 at 10:53 PM, Bob kb8tq  wrote:




Of course this *assumes* an electronic approach. Given that

it’s

moving
pretty slow and you
only are looking at fractions of a millisecond, one *could* do an
electro
mechanical design …...

Bob

There is interesting background on power grid frequency/time
adjustment

procedures here




https://en.wikipedia.org/wiki/Utility_frequency#Time_error_correction_(TEC)


and here
https://en.wikipedia.org/wiki/Electric_clock#Accuracy


--
WBW,

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--

Sent from my iPad 4.


--
WBW,

V.P.
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Re: [time-nuts] accurate 60 hz reference chips/ckts

[Jeremy Nichols]

I'm surprised Vlad is seeing as much as six seconds differential but maybe
I don't understand the experiment. I've done measurements of the line
frequency here in California and never seen much variation.

Jeremy


On Fri, Dec 15, 2017 at 9:02 AM Vlad  wrote:

>
>
> I have one of my project boxes, which monitor the main freq. Here is
> graph which reflect the time difference between of RTC (based on number
> of pulses from OCXO) and the "MAIN TIME" which is based on number of
> zero-cross events.
> The observation period is 486 hours.
>
>
>
>
> On 2017-12-14 23:13, Jim Harman wrote:
> > On Thu, Dec 14, 2017 at 10:53 PM, Bob kb8tq  wrote:
> >
> >>
> >>
> >> Of course this *assumes* an electronic approach. Given that it’s
> >> moving
> >> pretty slow and you
> >> only are looking at fractions of a millisecond, one *could* do an
> >> electro
> >> mechanical design …...
> >>
> >> Bob
> >>
> >> There is interesting background on power grid frequency/time
> >> adjustment
> > procedures here
> >
> https://en.wikipedia.org/wiki/Utility_frequency#Time_error_correction_(TEC)
> >
> > and here
> > https://en.wikipedia.org/wiki/Electric_clock#Accuracy
>
> --
> WBW,
>
> V.P.___
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Sent from my iPad 4.
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Re: [time-nuts] accurate 60 hz reference chips/ckts

[Vlad]

I have one of my project boxes, which monitor the main freq. Here is 
graph which reflect the time difference between of RTC (based on number 
of pulses from OCXO) and the "MAIN TIME" which is based on number of 
zero-cross events.

The observation period is 486 hours.




On 2017-12-14 23:13, Jim Harman wrote:

On Thu, Dec 14, 2017 at 10:53 PM, Bob kb8tq  wrote:




Of course this *assumes* an electronic approach. Given that it’s 
moving

pretty slow and you
only are looking at fractions of a millisecond, one *could* do an 
electro

mechanical design …...

Bob

There is interesting background on power grid frequency/time 
adjustment

procedures here
https://en.wikipedia.org/wiki/Utility_frequency#Time_error_correction_(TEC)

and here
https://en.wikipedia.org/wiki/Electric_clock#Accuracy


--
WBW,

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Re: [time-nuts] accurate 60 hz reference chips/ckts

[Jim Harman]

On Thu, Dec 14, 2017 at 10:53 PM, Bob kb8tq  wrote:

>
>
> Of course this *assumes* an electronic approach. Given that it’s moving
> pretty slow and you
> only are looking at fractions of a millisecond, one *could* do an electro
> mechanical design …...
>
> Bob
>
> There is interesting background on power grid frequency/time adjustment
procedures here
https://en.wikipedia.org/wiki/Utility_frequency#Time_error_correction_(TEC)

and here
https://en.wikipedia.org/wiki/Electric_clock#Accuracy
-- 

--Jim Harman
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Re: [time-nuts] accurate 60 hz reference chips/ckts

[Bob kb8tq]

Hi

My guess is that the “best design” would likely do a sample at some specific 
time of day.
Just when would depend a bit on your local grid and how it is fed and loaded. 
There are
definitely “it’s 6 PM and everybody just got home” issues with power line 
phase. 

Next question wold be how long to run your sample. Is a few minutes good 
enough? Is 
an hour overkill? There would be more than a little trial and error involved. 
You likely 
get to some SNR floor long before the 10’s of minutes point, even at the “best 
time of day”.

If you accept that you are getting 1x10^-4 sort of data, once a day gets you 
into the 1x10^-9
range. That’s not an unreasonable stability for a well warmed up OCXO for a few 
days to a 
few weeks. A sample a day may be quite adequate ….

Of course this *assumes* an electronic approach. Given that it’s moving pretty 
slow and you
only are looking at fractions of a millisecond, one *could* do an electro 
mechanical design …...

Bob



> On Dec 14, 2017, at 9:39 PM, Tom Van Baak  wrote:
> 
> Jim,
> 
>> You would want a filter time constant of several hours in the control loop
>> to smooth out the variations in the 60 Hz.
> 
> One can determine the appropriate time constant by looking at the ADEV of the 
> two clocks [1].
> 
> For GPS and OCXO the choice of time constant is fairly obvious. But the ADEV 
> for mains frequency isn't quite as pretty. So I'm not sure several hours 
> would work; maybe more like days or weeks? Here's a sample ADEV for power 
> line frequency:
> 
> http://leapsecond.com/pic/mains-adev-mdev-gnuplot-g4.png
> 
> I'd be curious if anyone has tried a mains disciplined oscillator and how 
> well it performed. Unlike a GPSDO, absolute phase can be lost (e.g., power 
> fail) so maybe use FLL instead of PLL. Shall we call it MFDO (mains frequency 
> disciplined oscillator)?
> 
> Hal and I have months, even years, or mains zero crossing timestamps so if 
> someone wants to simulate how well a MFDO might work let us know. Maybe just 
> adapt the gpsdo simulator [2].
> 
> /tvb
> 
> [1] some examples:
> www.thinksrs.com/assets/instr/PRS10/PRS10diag2LG.gif
> www.thinksrs.com/assets/instr/FS740/FS740_unlockedLG.gif
> www.thinksrs.com/assets/instr/FS740/FS740_lockedLG.gif
> www.leapsecond.com/pages/gpsdo
> 
> [2] gpsdo simulator project
> http://www.leapsecond.com/pages/gpsdo-sim/
> 
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Re: [time-nuts] accurate 60 hz reference chips/ckts

[Hal Murray]

t...@leapsecond.com said:
> For GPS and OCXO the choice of time constant is fairly obvious. But the
> ADEV for mains frequency isn't quite as pretty. So I'm not sure several
> hours would work; maybe more like days or weeks? Here's a sample ADEV for
> power line frequency: 

Has anybody investigated what the ADEV looks like if you plot something like 
one hour samples over a day?  That is is the ADEV in the morning when the 
temperature is warming up the same as the ADEV in the evening when the 
temperature is cooling off?



-- 
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Re: [time-nuts] accurate 60 hz reference chips/ckts

[Chris Caudle]

On Thu, December 14, 2017 8:39 pm, Tom Van Baak wrote:
> One can determine the appropriate time constant by looking at the ADEV of
> the two clocks

It appears that the appropriate design would use a local oscillator which
is stable to better than 10^-7 at 5 years and approximately 1200 days time
constant.  I would recommend using very low leakage capacitors in your RC
filter.

-- 
Chris Caudle


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Re: [time-nuts] accurate 60 hz reference chips/ckts

[Tim Shoppa]

That’s not a problem, that means you’re phase locked instead of just frequency 
locked.

This is the phase-nuts mailing list, right? :-)

Tim N3QE

> On Dec 14, 2017, at 6:19 PM, Alan Melia <alan.me...@btinternet.com> wrote:
> 
> I dont think working that way would give a stable clock in the UK. Our 
> frequency can vary more than the US but the number of cycles between 0800 on 
> one day and the next is mandated to be correct (I presume +/- 25 :-))  ). So 
> you would be chasing a moving target, and at no time of the day need the 
> frequency be 50.000Hz
> 
> Alan
> G3NYK
> 
> - Original Message - From: "Jim Harman" <j99har...@gmail.com>
> To: "Discussion of precise time and frequency measurement" 
> <time-nuts@febo.com>
> Sent: Thursday, December 14, 2017 10:08 PM
> Subject: Re: [time-nuts] accurate 60 hz reference chips/ckts
> 
> 
>> Since the power line has the desired long term stability but is poor on the
>> short term, I wonder if a solution might be to use it as the reference for
>> a "power line disciplined oscillator."
>> 
>> You would want a filter time constant of several hours in the control loop
>> to smooth out the variations in the 60 Hz.
>> 
>> Or it might be easier to rip the guts out of the Radio Shack clock, just
>> keeping the display, and drive the display with an Arduino and a DS3231 RTC
>> chip as the reference.
>> 
>>> On Thu, Dec 14, 2017 at 4:05 PM, Hal Murray <hmur...@megapathdsl.net> wrote:
>>> 
>>> 
>>> apollo...@gmail.com said:
>>> > Want to provide an accurate  (relatively accurate) 60 hz reference to > 
>>> > the
>>> > chip.   Some room inside for custom modifications.  Does a TCXO or
>>> similar
>>> > exist in a small package that provides 60 hz ticks?
>>> 
>>> I doubt if you will find a TCXO that puts out 60 Hz.  But it's only one
>>> chip
>>> to make a divider.  The trick is to do it in software rather than hardware.
>>> 
>>> The real question is what sort of error pattern are you interested in. The
>>> power company has good long term stability.  How good is your TCXO?  It
>>> would
>>> be fun to play with the numbers.  On the other hand, can you derive your 60
>>> Hz from a GPSDO?
>>> 
>>> --
>>> These are my opinions.  I hate spam.
>>> 
>>> 
>>> 
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>>> and follow the instructions there.
>>> 
>> 
>> 
>> 
>> -- 
>> 
>> --Jim Harman
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Re: [time-nuts] accurate 60 hz reference chips/ckts

[Alan Melia]

I dont think working that way would give a stable clock in the UK. Our 
frequency can vary more than the US but the number of cycles between 0800 on 
one day and the next is mandated to be correct (I presume +/- 25 :-))  ). So 
you would be chasing a moving target, and at no time of the day need the 
frequency be 50.000Hz


Alan
G3NYK

- Original Message - 
From: "Jim Harman" <j99har...@gmail.com>
To: "Discussion of precise time and frequency measurement" 
<time-nuts@febo.com>

Sent: Thursday, December 14, 2017 10:08 PM
Subject: Re: [time-nuts] accurate 60 hz reference chips/ckts


Since the power line has the desired long term stability but is poor on 
the

short term, I wonder if a solution might be to use it as the reference for
a "power line disciplined oscillator."

You would want a filter time constant of several hours in the control loop
to smooth out the variations in the 60 Hz.

Or it might be easier to rip the guts out of the Radio Shack clock, just
keeping the display, and drive the display with an Arduino and a DS3231 
RTC

chip as the reference.

On Thu, Dec 14, 2017 at 4:05 PM, Hal Murray <hmur...@megapathdsl.net> 
wrote:




apollo...@gmail.com said:
> Want to provide an accurate  (relatively accurate) 60 hz reference to 
> the

> chip.   Some room inside for custom modifications.  Does a TCXO or
similar
> exist in a small package that provides 60 hz ticks?

I doubt if you will find a TCXO that puts out 60 Hz.  But it's only one
chip
to make a divider.  The trick is to do it in software rather than 
hardware.


The real question is what sort of error pattern are you interested in. 
The

power company has good long term stability.  How good is your TCXO?  It
would
be fun to play with the numbers.  On the other hand, can you derive your 
60

Hz from a GPSDO?

--
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--Jim Harman
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Re: [time-nuts] accurate 60 hz reference chips/ckts

[Jim Harman]

Since the power line has the desired long term stability but is poor on the
short term, I wonder if a solution might be to use it as the reference for
a "power line disciplined oscillator."

You would want a filter time constant of several hours in the control loop
to smooth out the variations in the 60 Hz.

Or it might be easier to rip the guts out of the Radio Shack clock, just
keeping the display, and drive the display with an Arduino and a DS3231 RTC
chip as the reference.

On Thu, Dec 14, 2017 at 4:05 PM, Hal Murray  wrote:

>
> apollo...@gmail.com said:
> > Want to provide an accurate  (relatively accurate) 60 hz reference to the
> > chip.   Some room inside for custom modifications.  Does a TCXO or
> similar
> > exist in a small package that provides 60 hz ticks?
>
> I doubt if you will find a TCXO that puts out 60 Hz.  But it's only one
> chip
> to make a divider.  The trick is to do it in software rather than hardware.
>
> The real question is what sort of error pattern are you interested in.  The
> power company has good long term stability.  How good is your TCXO?  It
> would
> be fun to play with the numbers.  On the other hand, can you derive your 60
> Hz from a GPSDO?
>
> --
> These are my opinions.  I hate spam.
>
>
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Re: [time-nuts] accurate 60 hz reference chips/ckts

[Hal Murray]

apollo...@gmail.com said:
> Want to provide an accurate  (relatively accurate) 60 hz reference to the
> chip.   Some room inside for custom modifications.  Does a TCXO or similar
> exist in a small package that provides 60 hz ticks? 

I doubt if you will find a TCXO that puts out 60 Hz.  But it's only one chip 
to make a divider.  The trick is to do it in software rather than hardware.

The real question is what sort of error pattern are you interested in.  The 
power company has good long term stability.  How good is your TCXO?  It would 
be fun to play with the numbers.  On the other hand, can you derive your 60 
Hz from a GPSDO?

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Re: [time-nuts] accurate 60 hz reference chips/ckts

[Dave M]

National Semi used to make a chip (MM5369) that was designed specifically 
for that task, but it's long out of production.  I don't know of any 
off-the -shelf 60Hz generators, but it's pretty easy to build one.
Here are a couple of web pages that will generate a 60Hz crystal controlled 
signal.

http://electronicsmaker.com/em/admin/pdf/circuit_idea/60Hz%20CRYSTAL%20CONTROLLED%20TIME%20BASE.pdf
http://www.electronicecircuits.com/electronic-circuits/50hz-60hz-frequency-generator-circuit-using-crystal-oscillator

Accuracy of the generated 60Hz will depend, of course, upon the tempco of 
the crystal, the complete oscillator circuit itself, and on the accuracy to 
which you adjust the oscillator's frequency.


Cheers,
Dave M


Patrick Barthelow wrote:

PIcked up a couple of  large size Radio Shack  63-960 LED clocks with
Settable alarm, at local Goodwill store. $3.00 ea work great see
across room, loud Alarm, etc...


Barely missed, by seconds, getting a classic Hallicrafters General
coverage receiver
(not like say, S-38) but a larger light green metal box. nearly
perfect condx.  $25.00  with the famous h logo speaker  probably late
50s Vintage. :-(   Dang...
Checked LED clocks by ear and eye with WWV, They drift a few seconds
in
the course of a few days, and wander back and forth.  Thought AC mains
frequency was tighter than that. They use  an LM 8560 Clock chip.
Uses a switchable AC mains frequency reference pin  50/60 hz.
Want to provide an accurate  (relatively accurate) 60 hz reference to
the chip.   Some room inside for custom modifications.  Does a TCXO
or similar exist in a small package that provides 60 hz ticks?

Best, 73,   Pat Barthelow AA6EG
apol lo...@gmail.com


*"The most exciting phrase to hear in Science, the one that heraldsnew
discoveries,  is not "Eureka, I have found it!"but:*
"That's funny..."  Isaac Asimov
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Re: [time-nuts] accurate 60 hz reference chips/ckts

[Tom Van Baak]

Pat,

> They drift a few seconds in the course of a few days, and wander back and 
> forth.  

Yes, it's normal for AC mains to drift around by a few seconds over a day but 
it usually stays roughly on-time over weeks and months. Here's an old example 
of monitoring mains time & frequency for 45 days:

http://leapsecond.com/pages/mains/

> Does a TCXO or similar exist in a small package that provides 60 hz ticks?

If you have 10 MHz (XO, TCXO, etc.) you can convert to 60 Hz using a $1 PIC 
divider:

http://leapsecond.com/pic/src/pd60.asm
http://leapsecond.com/pic/src/pd60.hex

/tvb

- Original Message - 
From: "Patrick Barthelow" 
To: "Discussion of precise time and frequency measurement" 
Sent: Thursday, December 14, 2017 8:42 AM
Subject: [time-nuts] accurate 60 hz reference chips/ckts


> PIcked up a couple of  large size Radio Shack  63-960 LED clocks with
> Settable alarm, at local Goodwill store. $3.00 ea work great see across
> room, loud Alarm, etc...
> 
> 
> Barely missed, by seconds, getting a classic Hallicrafters General coverage
> receiver
> (not like say, S-38) but a larger light green metal box. nearly perfect
> condx.  $25.00  with the famous h logo speaker  probably late 50s Vintage.
> :-(   Dang...
> Checked LED clocks by ear and eye with WWV, They drift a few seconds in
> the course of a few days, and wander back and forth.  Thought AC mains
> frequency was tighter than that. They use  an LM 8560 Clock chip.  Uses a
> switchable AC mains frequency reference pin  50/60 hz.
> Want to provide an accurate  (relatively accurate) 60 hz reference to the
> chip.   Some room inside for custom modifications.  Does a TCXO or similar
> exist in a small package that provides 60 hz ticks?
> 
> Best, 73,   Pat Barthelow AA6EG
> apol lo...@gmail.com
> 
> 
> *"The most exciting phrase to hear in Science, the one that heraldsnew
> discoveries,  is not "Eureka, I have found it!"but:*
> "That's funny..."  Isaac Asimov

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