Re: [time-nuts] HP E1938A question

[Richard (Rick) Karlquist]

The main issue is that the oven will no longer be at the
crystal turnover temperature.  If you are using it in
a benign environment, you might not need the extreme
thermal performance enabled by being dead nuts on the
turnover.  You still have an oven with thermal gain
in the 100's of thousands.

The test software had the ability to sweep the oven temperature
and allow you to find the turn over.  There was some way to
then set the oven to this temperature.  I don't know if anyone
currently knows how to make the software do this anymore.
I knew at one time, but have long forgotten.

Rick N6RK

On 4/24/2017 5:41 AM, GandalfG8--- via time-nuts wrote:

I've just received an Ebay purchased E1938A, haven't tested it yet although
 I do have a 14 day return option, but unlike previous purchases of these
the serial number label is missing from the rear of the PCB so I have no
obvious  way of knowing if the crystal is matched to the PCB.

Does anybody know if there's any embedded information that can be accessed
that indicates the serial number of the board, or is there any other way I
can  check if the crystal and PCB are matched?

If not, what issues could I expect from an unmatched crystal and  PCB?

Nigel GM8PZR


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Re: [time-nuts] Frequency counter questions

[Chris Albertson]

On Sun, Apr 23, 2017 at 6:25 PM, Jerry Hancock  wrote:

>
>
> So to summarize, if I limit my high resolution to 99,999,999.999hz and use
> a gate of 1000 seconds, would that get me to .01hz?  If not, then what
> would the possible resolution be?
>

It is best to keep this kind of discussion on the list.  That way if some
one like me sys something dumb, it will get noticed and called out.

OK, so it seems you

(1) are interested in measuring frequency up to 100 MHz but no higher.
(2) want to use an STM32 ARM uP to
(3) Are using the older (and simpler) design that simply counts cycles and
divides by the gate time to measure frequency

If the above assumptions are wrong.  STOP reading now and post corrections
or additions

OK so we are good to go

I assume you know about and intend to use the built in counter/timmer on
the STM32.   You first step is to find out the maximum pule rate you can
place on that pin.  Lets guess it is 48 MHz. But you are a conservative
engineer an want to de-rate it to 24 MHz.

This means to measure up to 100 MHz you will need a prescaler that can
divide by 4.This will transform you maximum 100 MHz to a maximum of 25
MHz.   It will force you into using 4X longer gate time.   This is the only
reason to pre-scale, because you can't otherwise process the signal.

Now it is very simple.   You write software that starts the counters on the
desired pin and then your GPS sends a signal every one second (You do NOT
need to divide down the 10MHZ from a GPSDO because the GPS already has a
one pulse per second output that feeds the DO.)   SO every one second you
read the number of counts and keep doing this for as many seconds as you
need   After the gate time which might be one second or 4,000 seconds you
add up all the one second readings and compute the answer.

Actually you can do better given the excess computer power you have:  You
can output a frequency estimate after the first send and then each second
you can output a more accurate value until finally after 4,000 seconds out
have 0.001 Hz.   So in the first second you put up a display that is good
for +/- 4 hZ and then four seconds later you can be a 1.0 Hz and after an
hour 0.001 Hz

As I wrote before.   I use the "trigger" output of my old Tektronix scope
as input to my counter because the scopes trigger is MUCH better.   If you
own a 'scope this will save you a LOT of work as all you would need to
build is a voltage converter to take the trigger output to 3v3 volts for
the STM32.  The STM already can do rescaling and counting.Connect an
I2C display and you are done with the hardware.  For a better and cheaper
display, the STM32 can serve a web page and then you see the frequency on
your phone.






Chris Albertson
Redondo Beach, California
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Re: [time-nuts] Frequency counter questions

[Bob kb8tq]

Hi

Some of the process below is “not trivial”. One example:

You have a “gate” from the GPSDO and a “signal” from somewhere else. If you
want the STM to do the whole thing, the “gate” pin needs to get the job done in 
X +/-  1 cycles of the “signal” pin. Delay X (if it’s consistent) isn’t a 
problem. Having a
> +/- 1 cycle delay *is* a problem. The interrupt servicing structure in the MCU
may or may not be able to hit things +/- 10 ns or even +/- 100 ns.  Sometimes a
“lower power” MCU with simple code is better at this than a multi core gizmo 
running
a high level operating system. 

Lots of things to dig into.

Bob

> On Apr 24, 2017, at 12:45 PM, Chris Albertson  
> wrote:
> 
> On Sun, Apr 23, 2017 at 6:25 PM, Jerry Hancock  wrote:
> 
>> 
>> 
>> So to summarize, if I limit my high resolution to 99,999,999.999hz and use
>> a gate of 1000 seconds, would that get me to .01hz?  If not, then what
>> would the possible resolution be?
>> 
> 
> It is best to keep this kind of discussion on the list.  That way if some
> one like me sys something dumb, it will get noticed and called out.
> 
> OK, so it seems you
> 
> (1) are interested in measuring frequency up to 100 MHz but no higher.
> (2) want to use an STM32 ARM uP to
> (3) Are using the older (and simpler) design that simply counts cycles and
> divides by the gate time to measure frequency
> 
> If the above assumptions are wrong.  STOP reading now and post corrections
> or additions
> 
> OK so we are good to go
> 
> I assume you know about and intend to use the built in counter/timmer on
> the STM32.   You first step is to find out the maximum pule rate you can
> place on that pin.  Lets guess it is 48 MHz. But you are a conservative
> engineer an want to de-rate it to 24 MHz.
> 
> This means to measure up to 100 MHz you will need a prescaler that can
> divide by 4.This will transform you maximum 100 MHz to a maximum of 25
> MHz.   It will force you into using 4X longer gate time.   This is the only
> reason to pre-scale, because you can't otherwise process the signal.
> 
> Now it is very simple.   You write software that starts the counters on the
> desired pin and then your GPS sends a signal every one second (You do NOT
> need to divide down the 10MHZ from a GPSDO because the GPS already has a
> one pulse per second output that feeds the DO.)   SO every one second you
> read the number of counts and keep doing this for as many seconds as you
> need   After the gate time which might be one second or 4,000 seconds you
> add up all the one second readings and compute the answer.
> 
> Actually you can do better given the excess computer power you have:  You
> can output a frequency estimate after the first send and then each second
> you can output a more accurate value until finally after 4,000 seconds out
> have 0.001 Hz.   So in the first second you put up a display that is good
> for +/- 4 hZ and then four seconds later you can be a 1.0 Hz and after an
> hour 0.001 Hz
> 
> As I wrote before.   I use the "trigger" output of my old Tektronix scope
> as input to my counter because the scopes trigger is MUCH better.   If you
> own a 'scope this will save you a LOT of work as all you would need to
> build is a voltage converter to take the trigger output to 3v3 volts for
> the STM32.  The STM already can do rescaling and counting.Connect an
> I2C display and you are done with the hardware.  For a better and cheaper
> display, the STM32 can serve a web page and then you see the frequency on
> your phone.
> 
> 
> 
> 
> 
> 
> Chris Albertson
> Redondo Beach, California
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Re: [time-nuts] Frequency counter questions

[Bob kb8tq]

Hi

I believe what you are going to find is that the 3586 has an IF strip in it. 
It does a heterodyne process to the IF center frequency and then indicates
things from there. If the IF strip is out of alignment, you get a reading error.
Probably worth digging into the service manual on the 3586.

Bob

> On Apr 24, 2017, at 6:26 PM, Jerry Hancock  wrote:
> 
> Orin,  Thanks, this goes beyond interesting and I don’t know how you found 
> it.  I’ll be staring at this doc for the rest of the week.  I have a dozen or 
> so of the Nucleo boards around include the high end F7 types so I’ll see if I 
> can duplicate their code on the System Workbench they reference (and I have 
> installed).
> 
> This afternoon I hooked up the output of my 3586 F0 (with the GPSDO 
> reference) set to 15,000,000.0Mhz and then used my 3336 set to the same 
> (again with the GPSDO) to see if I had any creep on my TDS3054B scope after 
> syncing the two signals.  Just setting the 3336 to .001 higher causing the 
> sine waves to go out of sync noticeably in a minute.  It’s been running about 
> 2 hours and they still overlap perfectly when set to the same frequency.  
> 
> I think we all know what the issue is here in that the 3586 counter is 
> probably adding a count here or there.  It’s just curious that it never seems 
> to drop a count.  I would have thought I would see +.1 and -.1 with an equal 
> distribution over a reasonable period of time of a few minutes but I don’t; I 
> always see the +.1 or .0, never a 999.9 count (-.01).
> 
> If someone has a 5335 counter in the SF bay area they would like to unload, 
> please send me a note at meters at hanler dot com.
> 
> By the way, your Geller ref is still running perfectly.  I’ll have to send it 
> back to you for calibration soon as I think I have had it a year.
> 
> Jerry
> 
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Re: [time-nuts] Frequency counter questions

[Bob kb8tq]

Hi


> On Apr 24, 2017, at 3:49 PM, Chris Albertson  
> wrote:
> 
> On Mon, Apr 24, 2017 at 10:13 AM, Bob kb8tq  wrote:
> 
>> Hi
>> 
>> Some of the process below is “not trivial”. One example:
>> 
>> You have a “gate” from the GPSDO and a “signal” from somewhere else. If you
>> want the STM to do the whole thing, the “gate” pin needs to get the job
>> done in
>> X +/-  1 cycles of the “signal” pin. Delay X (if it’s consistent) isn’t a
>> problem. Having a
>>> +/- 1 cycle delay *is* a problem. The interrupt servicing structure in
>> the MCU
>> may or may not be able to hit things +/- 10 ns or even +/- 100 ns.
>> Sometimes a
>> “lower power” MCU with simple code is better at this than a multi core
>> gizmo running
>> a high level operating system.
> 
> -- 
> 
> C
> 
> The STM32 is in fact a low level micro controller that does not run an OS.


The STM being discussed is what they call an F7 part. A representative 
board running it is (= the one here on my desk):

http://www.st.com/en/evaluation-tools/32f769idiscovery.html 


It’s a board with 128 Mb of RAM and 512 Mb of flash. Among the other stuff on 
there is an RJ-45 ethernet jack There are a variety of RTOS options available
along with some cut down Linux versions. Trying to do ethernet without at least
an RTOS does not make much sense. It’s what they are calling an Cortex-M7 
rather than
a Cortex M4. There are a number of similar boards. If it’s an STM 32F7, the 
features
on the board will be similar to the one sitting here. 

Indeed the term STM32 covers a lot of ground and we have zigged and zagged 
a bit. Repeating all of the details from every earlier post in the thread makes
things even longer than they already are. Some amount of abbreviation is
inevitable. 

Bob

> 
> The chips contain counters and other hardware so most of the real-time
> stuff is not done in software.  You need to set this up so the on-chip
> hardware outside of the CPU is used.
> 
> There are two basic types of ARM computers, the "Cortex A" is what is in
> your phone and these have multi cores, GHz class clock speeds, gigabytes
> class memories and run an OS.   The other is ARM "Cortex M".  These are
> much smaller and run on about 100 uA of current with clocks about 100 MHz
> and kilobyte class memories and don't support running an OS.  These are
> used in embedded applications such as the throttle control in your car or a
> high end battery charger.  These cost about $1 each and the physical chip
> is about 3/8 inches square.I buy them quality one as a "Nucleo" board
> for about $12.  It is like an Arduino but about (literally) 100X better
> specs and half the cost.  About the same physical size.But for this
> counter project I'd use a generic STM32 board from eBay.  They sell for
> about $2 shipped
> 
> Take a look at this device.  It has a lot of power.  It can even be
> programmed using the Arduino IDE or the gnu toolchain and others.  You
> can't beat the price or the size.
> ...ebay.com/itm/New-STM32F103C8T6-ARM-STM32...
> 
> 
> 
> 
> 
> hris Albertson
> Redondo Beach, California
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Re: [time-nuts] Frequency counter questions

[Jerry Hancock]

Orin,  Thanks, this goes beyond interesting and I don’t know how you found it.  
I’ll be staring at this doc for the rest of the week.  I have a dozen or so of 
the Nucleo boards around include the high end F7 types so I’ll see if I can 
duplicate their code on the System Workbench they reference (and I have 
installed).

This afternoon I hooked up the output of my 3586 F0 (with the GPSDO reference) 
set to 15,000,000.0Mhz and then used my 3336 set to the same (again with the 
GPSDO) to see if I had any creep on my TDS3054B scope after syncing the two 
signals.  Just setting the 3336 to .001 higher causing the sine waves to go out 
of sync noticeably in a minute.  It’s been running about 2 hours and they still 
overlap perfectly when set to the same frequency.  

I think we all know what the issue is here in that the 3586 counter is probably 
adding a count here or there.  It’s just curious that it never seems to drop a 
count.  I would have thought I would see +.1 and -.1 with an equal distribution 
over a reasonable period of time of a few minutes but I don’t; I always see the 
+.1 or .0, never a 999.9 count (-.01).

If someone has a 5335 counter in the SF bay area they would like to unload, 
please send me a note at meters at hanler dot com.

By the way, your Geller ref is still running perfectly.  I’ll have to send it 
back to you for calibration soon as I think I have had it a year.

Jerry

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Re: [time-nuts] Frequency counter questions

[Hal Murray]

kb...@n1k.org said:
> You have a “gate” from the GPSDO and a “signal” from somewhere else. 
> If you
> want the STM to do the whole thing, the “gate” pin needs to get the job 
> done
> in  X +/-  1 cycles of the “signal” pin. Delay X (if it’s consistent) 
> isn’t
> a problem. Having a
> +/- 1 cycle delay *is* a problem. The interrupt servicing structure in the
> MCU may or may not be able to hit things +/- 10 ns or even +/- 100 ns.
> Sometimes a “lower power” MCU with simple code is better at this than a
> multi core gizmo running a high level operating system.  

Some of the counter/timer hardware has another register where the hardware 
will save a copy of the main counter when another signal happens.  If your 
gate time is the time between two pulses rather than the width of a single 
pulse, then all the software has to do is read that copy-register before the 
next pulse happens.


-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] Frequency counter questions

[Jerry Hancock]

Bob, I have an STM32F769 disco as well as the Nucleo version.  The big 
difference between the two is the LCD display on the Disco from what I remember.

I’ll play around with the code this week and report back.
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Re: [time-nuts] Frequency counter questions

[Bob kb8tq]

Hi

One advantage of keeping this on list — There are 3586B Guru’s running around 
here. 
I’m sure one of them will hop in to explain a bit more about what’s going on 
inside that
beast. Since (as you point out) you can put the same signal in as the 
reference, it may
be as simple as cranking pot R358242 to zero the reading …. maybe not. 

The road from “I wonder” to a full bench of TimeNut gear can be an amazingly 
short one.
Before you get into a build it yourself precision counter project, at least 
take a look at 
things like the HP 5334 and 5335 on the usual auction sites. They (and a large 
number
of other candidates) will do this job for you and do a number of future jobs as 
well. 
Depending on how the market is going, cost should be sub $150 delivered and sub
$100 with some time spent shopping (and maybe some risk). There’s also the 5386 
out there, not my favorite counter, but a wonderful thing if you have dyslexia 
and are 
typing 3586 :)

While the “I can wait for the reading” idea sounds good in theory. It rarely 
works well in 
practice. Temperature variations, warmup drift, and other stuff do happen in a 
lot less
than 10,000 seconds (or even 1,000 seconds). If you have to adjust something, 
even 
100 seconds can be a major pain. The constant 9 digits a second that the bench
counters provide can be very useful. 

Bob




> On Apr 24, 2017, at 3:06 PM, Jerry Hancock  wrote:
> 
> This is an exercise more than anything.  It started when I noticed the 
> counter in a 3586B I purchased was +1 count unless I dropped the input 
> frequency .25hz.  I was using my GPSDO reference for it and the 3336 it was 
> counting.  I then took my GPSDO and tried reading that directly and I see the 
> same thing.  This is annoying more than anything and I assume there is a 
> slight gate phase related issue.  I don’t have anything to read the jitter on 
> my GPSDO which is a Lucent RFTG-U with the REF1 and REF0 but since I am using 
> it as the reference and the signal under test, it shouldn’t matter at .1hz.  
> If I run the count over 3 minutes, the count is .923hz high consistently. To 
> put a finer point on it, reading 10,000,000.00hz from my GPSDO, It will read 
> consistently 10,000,000.1 or 10,000,000.0 with the distribution of each to 
> average 10,000,000.923 over 5 minutes.  If I drop the input frequency by 
> .25hz, it will read 10,000,000.0 without a 10,000,000.1 until the cows come 
> home.  I’v
 e 
> let it run about a day to check. 
> 
> So I was thinking, o.k., let’s put a frequency counter on the back to read 
> the F0 output signal rom the 3586B and see what it reads but I then realized 
> I don’t have anything that accurate.  I do have a lot of micro processors 
> around, everything from the lowly PIC thru the DSPIC to the STM32F7’s, F4’s 
> and if I have to, I will get a FPGA and go from there.  I could purchase an 
> HP 12 digit counter if I could find one locally as I am tired of paying 
> shipping but haven’t found one to date. 
> 
> So no really pressing reason for the counter other than just curious as to 
> what is causing the issue with the 3586B.  By the way, when I read any of the 
> WWV signals they count +.1hz as well under constant signal.  I am pretty sure 
> the 3586B is recognizing my reference input as the OCXO is dialed to 
> 10,000,000.0 and the standard oscillator is a little high at +.4 (if I 
> disconnect the OCXO strap) and I haven’t looked into it yet.
> 
> Thanks for the interest and help
> 
> Jerry
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Re: [time-nuts] Frequency counter questions

[Orin Eman]

Hi Jerry,

See AN4776 on st.com.  Section 2.6 looks particularly interesting.

Orin.

On Mon, Apr 24, 2017 at 12:06 PM, Jerry Hancock  wrote:

> This is an exercise more than anything.  It started when I noticed the
> counter in a 3586B I purchased was +1 count unless I dropped the input
> frequency .25hz.  I was using my GPSDO reference for it and the 3336 it was
> counting.  I then took my GPSDO and tried reading that directly and I see
> the same thing.  This is annoying more than anything and I assume there is
> a slight gate phase related issue.  I don’t have anything to read the
> jitter on my GPSDO which is a Lucent RFTG-U with the REF1 and REF0 but
> since I am using it as the reference and the signal under test, it
> shouldn’t matter at .1hz.  If I run the count over 3 minutes, the count is
> .923hz high consistently. To put a finer point on it, reading
> 10,000,000.00hz from my GPSDO, It will read consistently 10,000,000.1 or
> 10,000,000.0 with the distribution of each to average 10,000,000.923 over 5
> minutes.  If I drop the input frequency by .25hz, it will read 10,000,000.0
> without a 10,000,000.1 until the cows come home.  I’ve
>  let it run about a day to check.
>
> So I was thinking, o.k., let’s put a frequency counter on the back to read
> the F0 output signal rom the 3586B and see what it reads but I then
> realized I don’t have anything that accurate.  I do have a lot of micro
> processors around, everything from the lowly PIC thru the DSPIC to the
> STM32F7’s, F4’s and if I have to, I will get a FPGA and go from there.  I
> could purchase an HP 12 digit counter if I could find one locally as I am
> tired of paying shipping but haven’t found one to date.
>
> So no really pressing reason for the counter other than just curious as to
> what is causing the issue with the 3586B.  By the way, when I read any of
> the WWV signals they count +.1hz as well under constant signal.  I am
> pretty sure the 3586B is recognizing my reference input as the OCXO is
> dialed to 10,000,000.0 and the standard oscillator is a little high at +.4
> (if I disconnect the OCXO strap) and I haven’t looked into it yet.
>
> Thanks for the interest and help
>
> Jerry
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Re: [time-nuts] Frequency counter questions

[Chris Albertson]

On Mon, Apr 24, 2017 at 10:13 AM, Bob kb8tq  wrote:

> Hi
>
> Some of the process below is “not trivial”. One example:
>
> You have a “gate” from the GPSDO and a “signal” from somewhere else. If you
> want the STM to do the whole thing, the “gate” pin needs to get the job
> done in
> X +/-  1 cycles of the “signal” pin. Delay X (if it’s consistent) isn’t a
> problem. Having a
> > +/- 1 cycle delay *is* a problem. The interrupt servicing structure in
> the MCU
> may or may not be able to hit things +/- 10 ns or even +/- 100 ns.
> Sometimes a
> “lower power” MCU with simple code is better at this than a multi core
> gizmo running
> a high level operating system.

-- 

C

The STM32 is in fact a low level micro controller that does not run an OS.

The chips contain counters and other hardware so most of the real-time
stuff is not done in software.  You need to set this up so the on-chip
hardware outside of the CPU is used.

There are two basic types of ARM computers, the "Cortex A" is what is in
your phone and these have multi cores, GHz class clock speeds, gigabytes
class memories and run an OS.   The other is ARM "Cortex M".  These are
much smaller and run on about 100 uA of current with clocks about 100 MHz
and kilobyte class memories and don't support running an OS.  These are
used in embedded applications such as the throttle control in your car or a
high end battery charger.  These cost about $1 each and the physical chip
is about 3/8 inches square.I buy them quality one as a "Nucleo" board
for about $12.  It is like an Arduino but about (literally) 100X better
specs and half the cost.  About the same physical size.But for this
counter project I'd use a generic STM32 board from eBay.  They sell for
about $2 shipped

Take a look at this device.  It has a lot of power.  It can even be
programmed using the Arduino IDE or the gnu toolchain and others.  You
can't beat the price or the size.
...ebay.com/itm/New-STM32F103C8T6-ARM-STM32...





hris Albertson
Redondo Beach, California
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Re: [time-nuts] Frequency counter questions

[Jerry Hancock]

This is an exercise more than anything.  It started when I noticed the counter 
in a 3586B I purchased was +1 count unless I dropped the input frequency .25hz. 
 I was using my GPSDO reference for it and the 3336 it was counting.  I then 
took my GPSDO and tried reading that directly and I see the same thing.  This 
is annoying more than anything and I assume there is a slight gate phase 
related issue.  I don’t have anything to read the jitter on my GPSDO which is a 
Lucent RFTG-U with the REF1 and REF0 but since I am using it as the reference 
and the signal under test, it shouldn’t matter at .1hz.  If I run the count 
over 3 minutes, the count is .923hz high consistently. To put a finer point on 
it, reading 10,000,000.00hz from my GPSDO, It will read consistently 
10,000,000.1 or 10,000,000.0 with the distribution of each to average 
10,000,000.923 over 5 minutes.  If I drop the input frequency by .25hz, it will 
read 10,000,000.0 without a 10,000,000.1 until the cows come home.  I’ve 
 let it run about a day to check. 

So I was thinking, o.k., let’s put a frequency counter on the back to read the 
F0 output signal rom the 3586B and see what it reads but I then realized I 
don’t have anything that accurate.  I do have a lot of micro processors around, 
everything from the lowly PIC thru the DSPIC to the STM32F7’s, F4’s and if I 
have to, I will get a FPGA and go from there.  I could purchase an HP 12 digit 
counter if I could find one locally as I am tired of paying shipping but 
haven’t found one to date. 

So no really pressing reason for the counter other than just curious as to what 
is causing the issue with the 3586B.  By the way, when I read any of the WWV 
signals they count +.1hz as well under constant signal.  I am pretty sure the 
3586B is recognizing my reference input as the OCXO is dialed to 10,000,000.0 
and the standard oscillator is a little high at +.4 (if I disconnect the OCXO 
strap) and I haven’t looked into it yet.

Thanks for the interest and help

Jerry
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[time-nuts] HP E1938A question

[GandalfG8--- via time-nuts]

I've just received an Ebay purchased E1938A, haven't tested it yet although 
 I do have a 14 day return option, but unlike previous purchases of these  
the serial number label is missing from the rear of the PCB so I have no 
obvious  way of knowing if the crystal is matched to the PCB.
 
Does anybody know if there's any embedded information that can be accessed  
that indicates the serial number of the board, or is there any other way I 
can  check if the crystal and PCB are matched?
 
If not, what issues could I expect from an unmatched crystal and  PCB?
 
Nigel GM8PZR
 
 
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Re: [time-nuts] Frequency counter questions

[Bob kb8tq]

Hi

Let’s back off a bit. 

To most of us, a 12 digit counter displays 12 digits regardless of the 
frequency 
you put into it. That’s been the way good bench counters have done it since 
the early 1970’s. Typically the number of digits is specified at a one second 
gate time. An HP 5335 is one example. It is called a 9 digit (or more properly 
9 digit per second) counter. Over the last 30 years, the last “per second” part
has commonly been dropped. 

In the world of computers, the number of digits displayed is not the big deal
it was back in the days of nixie tubes. As Chris points out, comping up a 
display
is what things like the F7 are intended to do. The Discovery boards are a 
cheap way to get this running. 

Thus the confusion.

If you prescale you divide down the input frequency. The counter is “reading”
the divided down frequency. That’s not a big deal on a modern counter. It is
a big deal on an old style counter On an old style counter, you don’t get a 
constant number of digits at a given gate time. If you put in 1,000 cycles (also
called Hertz ..) and count them for one second, there will be four digits 
displayed. 
If you prescale the signal by 100, your counter will display 10 (two digits 
displayed).
In general prescalers are something to avoid on an old style counter.

With a modern 9 digit counter, if you put in 1,000 Hz and ran for a second you 
would
get 1,000.123456 on the display. You might or might not get good accuracy in 
all those digits. That’s roughly what the display would look like. 

So now back to the real questions: 

What is your input signal? How high is it in frequency? Is there a range of 
frequencies? 
Is it modulated? …..

What kind of accuracy are you after? (resolution and accuracy are two different 
things).

Is this a learning experience? Would a purchased counter for < $100 be an 
equally good
answer? 

Is the count it’s self significant? There are *many* different ways to measure 
frequency 
other than a straight counter. 

Lots of fun.

Bob


> On Apr 23, 2017, at 9:25 PM, Jerry Hancock  wrote:
> 
> For some reason I am not getting the individual emails so I apologize for not 
> replying more promptly.  I’ll have to check my profile.
> 
> As far as I can tell from the notes, and by the way, the number of notes was 
> why I was trying to move this off list, to get to .001hz I need to measure 
> over 1000 seconds.  This is ok.  Since I am looking for an average over time 
> anyway, this is not a problem.  By the way I am using a GPSDO and planned to 
> use it divided down for the gate.
> 
> The only reason I mentioned a prescaler was that there was a 12 digit counter 
> schematic on the web that looked pretty complete.  This person used a 
> prescaler and I was trying to wrap my head around how this helped with 
> resolution and I guess from the replies, that is not a practical solution 
> (using a prescaler) when you want high resolution unless I use the inverse 
> operation which I can’t remember what it is called off the top of my head.
> 
> I’ve seen some HP 12 digit counters but since I have a GPSDO and who knows 
> how many micro development boards around here, I thought I would take a run 
> at it.
> 
> So to summarize, if I limit my high resolution to 99,999,999.999hz and use a 
> gate of 1000 seconds, would that get me to .01hz?  If not, then what would 
> the possible resolution be?
> 
> Thanks for all the input, very helpful.
> 
> Jerry
> 
> 
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Re: [time-nuts] Frequency counter questions

[Tim Shoppa]

Jerry, for a 100MHz PIC based counter a prescaler will be necessary. But it 
will not be necessary for a 30MHz counter.

Prescalers do not have to be by divisors of 10. I recall the PIC counter input 
to be good to 50MHz so the prescaler could just be a divide by two if you need 
a 100MHz counter and it *has* to be done by a PIC.

Of course there are lots of logic families that don't need a prescaler at 
100MHz and could be used to make a frequency counter.

Most frequency counter designs out there on the net introduce an extra count or 
two due to flawed conception of gate.

Tim N3QE

Sent from my VAX-11/780

> On Apr 23, 2017, at 9:25 PM, Jerry Hancock  wrote:
> 
> For some reason I am not getting the individual emails so I apologize for not 
> replying more promptly.  I’ll have to check my profile.
> 
> As far as I can tell from the notes, and by the way, the number of notes was 
> why I was trying to move this off list, to get to .001hz I need to measure 
> over 1000 seconds.  This is ok.  Since I am looking for an average over time 
> anyway, this is not a problem.  By the way I am using a GPSDO and planned to 
> use it divided down for the gate.
> 
> The only reason I mentioned a prescaler was that there was a 12 digit counter 
> schematic on the web that looked pretty complete.  This person used a 
> prescaler and I was trying to wrap my head around how this helped with 
> resolution and I guess from the replies, that is not a practical solution 
> (using a prescaler) when you want high resolution unless I use the inverse 
> operation which I can’t remember what it is called off the top of my head.
> 
> I’ve seen some HP 12 digit counters but since I have a GPSDO and who knows 
> how many micro development boards around here, I thought I would take a run 
> at it.
> 
> So to summarize, if I limit my high resolution to 99,999,999.999hz and use a 
> gate of 1000 seconds, would that get me to .01hz?  If not, then what would 
> the possible resolution be?
> 
> Thanks for all the input, very helpful.
> 
> Jerry
> 
> 
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Re: [time-nuts] Frequency counter questions

[Bob kb8tq]

Hi


> On Apr 24, 2017, at 6:54 PM, Hal Murray  wrote:
> 
> 
> kb...@n1k.org said:
>> You have a “gate” from the GPSDO and a “signal” from somewhere else. If you
>> want the STM to do the whole thing, the “gate” pin needs to get the job done
>> in  X +/-  1 cycles of the “signal” pin. Delay X (if it’s consistent) isn’t
>> a problem. Having a
>> +/- 1 cycle delay *is* a problem. The interrupt servicing structure in the
>> MCU may or may not be able to hit things +/- 10 ns or even +/- 100 ns.
>> Sometimes a “lower power” MCU with simple code is better at this than a
>> multi core gizmo running a high level operating system.  
> 
> Some of the counter/timer hardware has another register where the hardware 
> will save a copy of the main counter when another signal happens.  If your 
> gate time is the time between two pulses rather than the width of a single 
> pulse, then all the software has to do is read that copy-register before the 
> next pulse happens.

Works a bit better if the input is edge sensing rather than level sensing ….
(copy on positive edge vs keep copying the whole time the input is high)

Bob


> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
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