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FREQ COUNTER help
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Paul Taylor
electronics forum beginner


Joined: 10 Feb 2005
Posts: 45

PostPosted: Wed Jul 19, 2006 8:42 am    Post subject: Re: FREQ COUNTER help Reply with quote

"John Fields" <jfields@austininstruments.com> wrote in message > ---
Quote:
---
It is if you've got a low frequency and you've only got a short time
to measure it, but you've got different kind of problem if you want
to determine the frequency of a 1Hz signal in 1 millisecond.

Why don't you tell us _exactly_ what it is you're trying to
accomplish? That way we can probably help you decide on a good way
to go about getting it done instead of wasting a lot of time
guessing about what you want.

Type your reply _after_ the arrow. :-)

John Fields
Professional Circuit Designer

Hi John sorry for the delay in replying the thread has sort of like split of
in all direction and i have been having problems with my news server, in a
nutshell

I have bought in a photometer which in turn is connected to a bought in
pulse amplifier discriminator (pad) this is from electron tubes part AD7,
this needs to be feed into a counter to count the pulses which I am to
build, the telemetry system is already in
place which I haven't built, the bottom line is I need to count the output
from the pad which counts the sodium particles and get this count back down
to earth.

I have a 1khz gate pulse for the count and 833khz (Clock signal) for sending
out the data via the telemetry system which is already in the rocket, i need
to count upto 2 power 16 or 65536 it is expected to loose the first bit so
32768 is an excepted maximum count.

Thanks
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Paul Taylor
electronics forum beginner


Joined: 10 Feb 2005
Posts: 45

PostPosted: Wed Jul 19, 2006 8:59 am    Post subject: Re: FREQ COUNTER help Reply with quote

"John Fields" <jfields@austininstruments.com> wrote in message
news:5bpqb29bna4s0i17l5i24mde3u04a6ect1@4ax.com...
Quote:
On Tue, 18 Jul 2006 14:31:37 +0000 (UTC), kensmith@green.rahul.net
(Ken Smith) wrote:

In article <aS5vg.33528$Nb2.617461@news1.nokia.com>,
rick H <rik_nntp@dsl.pipex.com> wrote:
[....]
How do you know that the emission of these photons isn't bursty -
nothing for a while, and then 100 in a nanosecond? If that's the case,
your 10ppm guess is hopeless. You need to know the *maximum* expected
event-rate in order to determine the counter's maximum increment rate
and in order to know the accuracy of the ms clock required for +/- 1
photon "resolution".
k
Hmmmm ... maybe this calls for a flash ADC to estimate the number of
coincident photons and an adder instead of a counter.

---
Great idea! I was also thinking if the width of a single photon
event was specified, then smearing could be used to gate a fast
clock which would actually provide the edges for the counter's clock
as well as the 1ms window.


--
John Fields
Professional Circuit Designer

John you said about smearing could be used sorry but I don't understand what
this is? can you explain.
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Bill Sloman
electronics forum Guru


Joined: 12 May 2005
Posts: 1080

PostPosted: Wed Jul 19, 2006 9:46 am    Post subject: Re: FREQ COUNTER help Reply with quote

Paul Taylor wrote:
Quote:
bill.sloman@ieee.org> wrote in message
news:1153276921.756125.300290@m73g2000cwd.googlegroups.com...

Phil Allison wrote:
bill.slowman@ieee.org

No, Phil isn't a troll - who are people who posts stuff that they
expect to generate controversy.


** Got that right at least.

All the rests was just another load of fucking bollocks from a demented,
grossly autistic arrogant old fool.

Peeeukeeee.

Like I said, Phil's abuse is tediously repetitive - but he lives in
Sydney, and wouldn't know any better.

--
Bill Sloman, Nijmegen - but educated in Melbourne


Bill I think it is best if you ignore him and not get pulled into his
in-mature childish temper tantrums, that is probley what he wants any way
back to the job in hand. I have been having problems with my email so have
been unable to reply to any postings so far i have got a counter working
with a 1sec gate pulse ect... but when i go to 1msec this is where the
problems start?

If the system works with a one second window, it ought to work with a
1millisecond window - logic doesn't usually start fallig over before
you get down to micorsecond time intervals.

As for rattling Phil Allison's cage - the longer we keep him mad, the
better the chance that he will blow a blood vessel and lose his
capacity to manipulate a keyboard. This would be a rather pyschopathic
motivation if one considered Phil to be fully human.

--
Bill Sloman, Nijmegen
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YD
electronics forum Guru Wannabe


Joined: 20 May 2005
Posts: 142

PostPosted: Wed Jul 19, 2006 10:54 am    Post subject: Re: FREQ COUNTER help Reply with quote

On Wed, 19 Jul 2006 09:42:31 +0100, "Paul Taylor"
<paul.taylor@uea.ac.uk> wrote:

Quote:
"John Fields" <jfields@austininstruments.com> wrote in message > ---
---
It is if you've got a low frequency and you've only got a short time
to measure it, but you've got different kind of problem if you want
to determine the frequency of a 1Hz signal in 1 millisecond.

Why don't you tell us _exactly_ what it is you're trying to
accomplish? That way we can probably help you decide on a good way
to go about getting it done instead of wasting a lot of time
guessing about what you want.

Type your reply _after_ the arrow. :-)

John Fields
Professional Circuit Designer

Hi John sorry for the delay in replying the thread has sort of like split of
in all direction and i have been having problems with my news server, in a
nutshell

I have bought in a photometer which in turn is connected to a bought in
pulse amplifier discriminator (pad) this is from electron tubes part AD7,
this needs to be feed into a counter to count the pulses which I am to
build, the telemetry system is already in
place which I haven't built, the bottom line is I need to count the output
from the pad which counts the sodium particles and get this count back down
to earth.

I have a 1khz gate pulse for the count and 833khz (Clock signal) for sending
out the data via the telemetry system which is already in the rocket, i need
to count upto 2 power 16 or 65536 it is expected to loose the first bit so
32768 is an excepted maximum count.

Thanks


In effect, what you're planning to do is open the gate for 1 ms, close
the gate, send the accumulated counts at 833 kHz by some modulation
scheme, reset the counter, open the gate, and so on. Sounds feasible.
If you want contiguous time slices things get a bit more complicated.
Let's see. After 1 ms shift out the data, reset counter, let
accumulate while the shifted data is transmitted. Sounds good if your
transmission scheme can handle it.

- YD.

--
Remove HAT if replying by mail.
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Paul Taylor
electronics forum beginner


Joined: 10 Feb 2005
Posts: 45

PostPosted: Wed Jul 19, 2006 10:56 am    Post subject: Re: FREQ COUNTER help Reply with quote

"YD" <ydtechHAT@techie.com> wrote in message
Quote:
In effect, what you're planning to do is open the gate for 1 ms, close
the gate, send the accumulated counts at 833 kHz by some modulation
scheme, reset the counter, open the gate, and so on. Sounds feasible.
If you want contiguous time slices things get a bit more complicated.
Let's see. After 1 ms shift out the data, reset counter, let
accumulate while the shifted data is transmitted. Sounds good if your
transmission scheme can handle it.

- YD.

--
Remove HAT if replying by mail.
that is it in a nutshell, i can get it to run a 1sec gate but not 1msec?
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John Fields
electronics forum Guru


Joined: 24 Mar 2005
Posts: 3260

PostPosted: Wed Jul 19, 2006 1:02 pm    Post subject: Re: FREQ COUNTER help Reply with quote

On 18 Jul 2006 19:52:49 -0700, bill.sloman@ieee.org wrote:


Quote:
Since you were the one who didn't know how rotten a simple TTL one-shot
actually is, and had to be dragged through the calculations repeatedly
until the penny finally dropped, I think you had better give up that
second bottle of chardonnay until your brain gets back into contact
with reality.

---
TTL one-shots aren't horrible, they just have potentially large
worst-case timing variations which can easily be trimmed out with a
variable resistor.

LOL, it wasn't me who couldn't tell whether the circuit was charging
or discharging the capacitor, and it wasn't me who wanted to use the
impossible-to-reach Vcc and ground for the "worst-case" scenarios
either. As far as being dragged through the calculations goes, ISTR
it was you who had to be shown, over and over, that the numbers you
were coming up with were bogus until you finally realized what you
were doing wrong. After all, It wasn't me who wrote: "s**t. I blew
it." was it?

--
John Fields
Professional Circuit Designer
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Ken Smith
electronics forum Guru


Joined: 06 May 2005
Posts: 1727

PostPosted: Wed Jul 19, 2006 2:52 pm    Post subject: Re: FREQ COUNTER help Reply with quote

In article <5bpqb29bna4s0i17l5i24mde3u04a6ect1@4ax.com>,
John Fields <jfields@austininstruments.com> wrote:
[.. ADC ..]
Quote:
Great idea! I was also thinking if the width of a single photon
event was specified, then smearing could be used to gate a fast
clock which would actually provide the edges for the counter's clock
as well as the 1ms window.

If the detector has a "dead time" neither of these ideas will work well.
The numbers can be "dead time corrected" after the fact with a little
math.
--
--
kensmith@rahul.net forging knowledge
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Bill Sloman
electronics forum Guru


Joined: 12 May 2005
Posts: 1080

PostPosted: Wed Jul 19, 2006 3:01 pm    Post subject: Re: FREQ COUNTER help Reply with quote

John Fields wrote:
Quote:
On 18 Jul 2006 19:52:49 -0700, bill.sloman@ieee.org wrote:


Since you were the one who didn't know how rotten a simple TTL one-shot
actually is, and had to be dragged through the calculations repeatedly
until the penny finally dropped, I think you had better give up that
second bottle of chardonnay until your brain gets back into contact
with reality.

---
TTL one-shots aren't horrible, they just have potentially large
worst-case timing variations which can easily be trimmed out with a
variable resistor.

Easily trimmd out? The resistor has got to be low enough to sink 2mA
from an input at 0.8V into an output at 0.4V which is to say, 200R or
less, so it needs to be trimmable down to 20R to get your 10:1
turn-down. The output impedance of a TTL output in the high state when
sourcing curent is already about 20R, so this is a very dubious
propostion.

Throw in that you are going to have to select your capacitor out of the
E6 range - each value about 1,5 times the one below it, and life gets
difficult.

And neither pots nor the time to trim them is all that cheap, and
making space for the pot on the PCB as well as making sure that final
test can get at the pot with a screwdriver (don't laugh = I've seen
draughtspersons screw that up) doesn't help either.

Sensible people use purpose-designed monostables, if they have to use a
monostable at all - when my junior engineers wanted to use bodged
single gate monostables we almost always solved the problem by making
the relevant bit of the circuit by clocking the data into a latch at
the right time, which offers many fewer wau=ys if getting things wrong.

Quote:
LOL, it wasn't me who couldn't tell whether the circuit was charging
or discharging the capacitor,

I did get a little bored with the process and wasn't giving it my full
attention.

Quote:
and it wasn't me who wanted to use the
impossible-to-reach Vcc and ground for the "worst-case" scenarios
either.

Vcc and ground may be impossible to reach, but they do have the virtue
that it is quite impossible for the output to go higher or lower, no
matter what you assume about the transistors involved - chose these as
extreme values and you can at least be confident that real examples of
the circuit won't behave any worse. That is what "worst case" design is
all about, not clever guesswork (rather less than clever in your case)
about whee the boundaries "really" lie.

Quote:
As far as being dragged through the calculations goes, ISTR
it was you who had to be shown, over and over, that the numbers you
were coming up with were bogus until you finally realized what you
were doing wrong. After all, It wasn't me who wrote: "s**t. I blew
it." was it?

"s**t, I blew it" referred to a failure of attention, not of
comprehension.

My numbers weren't bogus, they merely represented more conservative
(more risk-averse) choices of extreme conditions. Even when we choked
the worse cases down to numbers that you'd guessed to be okay, the
broad-brush conclusion stayed where it was when I started out.

It was you who didn't know that TTL outputs have a guaranteed minimum
high level of 2.4V, not the 3.3V you pulled from some cockanamy
web-site when you should have been reading the datasheet.

--
Bill Sloman, Nijmegen
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Paul Taylor
electronics forum beginner


Joined: 10 Feb 2005
Posts: 45

PostPosted: Wed Jul 19, 2006 3:07 pm    Post subject: Re: FREQ COUNTER help Reply with quote

"Ken Smith" <kensmith@green.rahul.net> wrote in message
news:e9lgv4$gmp$5@blue.rahul.net...
Quote:
In article <5bpqb29bna4s0i17l5i24mde3u04a6ect1@4ax.com>,
John Fields <jfields@austininstruments.com> wrote:
[.. ADC ..]
Great idea! I was also thinking if the width of a single photon
event was specified, then smearing could be used to gate a fast
clock which would actually provide the edges for the counter's clock
as well as the 1ms window.

If the detector has a "dead time" neither of these ideas will work well.
The numbers can be "dead time corrected" after the fact with a little
math.
--
--
kensmith@rahul.net forging knowledge


And how could i correct the dead time ken?
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John Fields
electronics forum Guru


Joined: 24 Mar 2005
Posts: 3260

PostPosted: Wed Jul 19, 2006 3:48 pm    Post subject: Re: FREQ COUNTER help Reply with quote

On Wed, 19 Jul 2006 09:42:31 +0100, "Paul Taylor"
<paul.taylor@uea.ac.uk> wrote:

Quote:
"John Fields" <jfields@austininstruments.com> wrote in message > ---
---
It is if you've got a low frequency and you've only got a short time
to measure it, but you've got different kind of problem if you want
to determine the frequency of a 1Hz signal in 1 millisecond.

Why don't you tell us _exactly_ what it is you're trying to
accomplish? That way we can probably help you decide on a good way
to go about getting it done instead of wasting a lot of time
guessing about what you want.

Type your reply _after_ the arrow. :-)

John Fields
Professional Circuit Designer

Hi John sorry for the delay in replying the thread has sort of like split of
in all direction and i have been having problems with my news server, in a
nutshell

I have bought in a photometer which in turn is connected to a bought in
pulse amplifier discriminator (pad) this is from electron tubes part AD7,
this needs to be feed into a counter to count the pulses which I am to
build, the telemetry system is already in
place which I haven't built, the bottom line is I need to count the output
from the pad which counts the sodium particles and get this count back down
to earth.

I have a 1khz gate pulse for the count and 833khz (Clock signal) for sending
out the data via the telemetry system which is already in the rocket, i need
to count upto 2 power 16 or 65536 it is expected to loose the first bit so
32768 is an excepted maximum count.

---
Something is very wrong here.

The AD7 has a pulse-pair resolution of 24ns which, AIUI, is the
minimum quiet time which must elapse between input pulses from the
PMT in order for them to be distinguished as separate events.

Now let's say that you've got a perfect system with super-duper PMT
which puts out 10ns pulses which can trigger the AD7 every 34ns.
The best you could do then, would be to have a train of pulses
coming out of the AD7 which would look like this:

->| |<--34ns
_ _ _
__| |_____| |_____| |____


Since 1ms is a million nanoseconds, the number of pulses coming out
of the AD7 in that time would be:


1000000ns
----------- = 29411 pulses
34ns

Which is fewer, even, than your new 32768 count spec.


Also, I don't know what you mean by "loose the first bit" and how
that would degrade the count by a factor of 2.


--
John Fields
Professional Circuit Designer
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John Fields
electronics forum Guru


Joined: 24 Mar 2005
Posts: 3260

PostPosted: Wed Jul 19, 2006 3:49 pm    Post subject: Re: FREQ COUNTER help Reply with quote

On Wed, 19 Jul 2006 09:59:25 +0100, "Paul Taylor"
<paul.taylor@uea.ac.uk> wrote:


Quote:
John you said about smearing could be used sorry but I don't understand what
this is? can you explain.

---
I was thinking about something else, sorry.


--
John Fields
Professional Circuit Designer
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John Fields
electronics forum Guru


Joined: 24 Mar 2005
Posts: 3260

PostPosted: Wed Jul 19, 2006 4:28 pm    Post subject: Re: FREQ COUNTER help Reply with quote

On 19 Jul 2006 08:01:31 -0700, bill.sloman@ieee.org wrote:

Quote:
Easily trimmd out?

---
Your post and this thread actually should be part of "flag
desecration"' so if you'd care to take it over there I'll be happy
to reply to it.


--
John Fields
Professional Circuit Designer
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John Fields
electronics forum Guru


Joined: 24 Mar 2005
Posts: 3260

PostPosted: Wed Jul 19, 2006 7:35 pm    Post subject: Re: FREQ COUNTER help Reply with quote

On Wed, 19 Jul 2006 08:09:01 GMT, rick H <rik_nntp@dsl.pipex.com>
wrote:

Quote:
John Fields <jfields@austininstruments.com> wrote:
On Tue, 18 Jul 2006 23:07:09 +0100, Rick <rik_nntp@dsl.pipex.com
wrote:

John Fields wrote:

On Tue, 18 Jul 2006 14:02:46 GMT, rick H <rik_nntp@dsl.pipex.com
wrote:
John Fields <jfields@austininstruments.com> wrote:
It's doubtful whether he could generate the time base for the enable
with just a ?C since he needs something with an accuracy of around
10ppm to generate the enable window in order to get the +/- 1 photon
resolution he's looking for. Maybe less than 10ppm, that's just a
first cut look at it.

How do you know that the emission of these photons isn't bursty -

---
I don't, but so far in the discussion it doesn't matter.

It matters plenty if you start guessing the accuracy of the
enable required to achieve an accuracy (though you called it
resolution) of +/-1 event. Which you did.

---
The assumption, a*****le, for the porpoise of describing the initial
archietexture, was that the 65536 pluses were spaced equidistantly
in a window 1.0 pulse or minus something millie seconds wide.

If they were equidistant (only ever *your* assumption, not *the*
assumption), then where did your figure of 10ppm materialize from and
why would that figure need to be a "first-cut look"? Can't you take the
numbers 1e-3 and 65536 and divide them?


Why are you getting your panties in such a bunch about what _might_
be happening in that window before the OP's even gotten back to us
with what he _really_ wants?

No wedgies here, old chap. I simply pointed out that your assumptions
were flawed and hence your post was meaningless. You're the one getting
all steamed up.

I'll leave you to post the last insult, I suspect it's your style.

Rather than an insult, I'll leave you with a question. How do you
propose that the input signal to the counter will be "bursty"?


--
John Fields
Professional Circuit Designer
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I.F.
electronics forum Guru


Joined: 30 Mar 2006
Posts: 407

PostPosted: Wed Jul 19, 2006 8:32 pm    Post subject: Re: FREQ COUNTER help Reply with quote

"Ken Smith" <kensmith@green.rahul.net> wrote in message
news:e9hafp$84b$3@blue.rahul.net...
Quote:
In article <12bncevgot1dm49@corp.supernews.com>,
Meindert Sprang <ms@NOJUNKcustomORSPAMware.nl> wrote:
[...]
Ok, so use a 16 bit counter which you read-and-reset every ms. You need a
VHF capable prescaler (/256 or so) and then feed it into some counter or
microcontroller with an external counter input.

... or ...

You can use two counter circuits and toggle between them every ms. This
way you've got a little time to latch the value away.

Or use a C/R differentiator (spike generator) to pulse a row of D-flipflops
to latch the data ready for the devcoder driver.
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YD
electronics forum Guru Wannabe


Joined: 20 May 2005
Posts: 142

PostPosted: Wed Jul 19, 2006 9:45 pm    Post subject: Re: FREQ COUNTER help Reply with quote

On Wed, 19 Jul 2006 11:56:51 +0100, "Paul Taylor"
<paul.taylor@uea.ac.uk> wrote:

Quote:
"YD" <ydtechHAT@techie.com> wrote in message
In effect, what you're planning to do is open the gate for 1 ms, close
the gate, send the accumulated counts at 833 kHz by some modulation
scheme, reset the counter, open the gate, and so on. Sounds feasible.
If you want contiguous time slices things get a bit more complicated.
Let's see. After 1 ms shift out the data, reset counter, let
accumulate while the shifted data is transmitted. Sounds good if your
transmission scheme can handle it.

- YD.

--
Remove HAT if replying by mail.
that is it in a nutshell, i can get it to run a 1sec gate but not 1msec?


If the 833 kHz is the data clock, you can easily get 1 ms time-slices.
In the second scheme suggested shift the data to a uC and let it chomp
on the bits on the way to the modulator. You may even have space
enough in a transmission slice for data from some other sensor. I
assume transmission is VHF.

But first take care of the original question, what to use for a
front-end in the counter.

This is not really my field. I know enough to dream up something that
might be workable but the practical implentation would be a bit of a
job.

- YD.

--
Remove HAT if replying by mail.
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