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FREQ COUNTER help
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Rick H
electronics forum beginner


Joined: 19 Jul 2005
Posts: 18

PostPosted: Fri Jul 21, 2006 12:26 pm    Post subject: Re: FREQ COUNTER help Reply with quote

Paul Taylor <paul.taylor@uea.ac.uk> wrote:
Quote:
"Rick" <rik_nntp@dsl.pipex.com> wrote in message
news:iqGdnQDDtYFxciLZnZ2dnUVZ8qWdnZ2d@pipex.net...
In the case that of a discriminator with
memory and a dead-time, that simplifies to "what's the length of that
memory of an event plus the deadtime", which is what you're now saying.

---
No, it's what _you're_ now saying. I always postulated a train of
maximum-density detectable pulses and you're only now coming around
to it while trying to make it seem like it's been your position all
along.

Trouble is, you define maximum density (see 2 or 3 of your posts ago) in
terms of the 1ms reporting period and in terms of the bit-width of the
counter. Better tell the PAD your assumptions.


--
Rick

Rick 2 to the power of 16 is the maximum counter rate required!

Hi Paul,

Yes, we understand that you're designing the system to detect a maximum
of 65536 events per millisecond (Although I'm going to guess that
actually your maximum count is 65535, because that's the most a 16-bit
counter will give you).

This sub-thread started because John was estimating the accuracy
required of the ms timer - the one that says "stop counting and tell me
what you've got" - to be sure that the count is accurate to one event.
Well, you may not even be interested in 1-event accuracy, but that's the
way the conversation turned!

Clearly, the most error you can tolerate on a timer in order to make
sure the count is accurate to 1 event is related to the *minimum* time
between events. As an example (with made-up numbers, John), if your
clock toggles early by 10us and if the PAD happened to detect an extra
2 events in that extra 10us before the clock *should* have toggled, then
your count is out by two. The only way to ensure the count is accurate
to one event is to make sure that the ms clock transitions at 1ms +/-
the smallest possible time-gap between events.

John went about it in a different way - , he assumed that the PAD
would change its output (at its fastest, when lots of photons are being
detected) exactly 65536 times per ms. Obviously if that actually _was_
the case, then the minumum time between events becomes 1ms/65536 and that
therefore defines the accuracy of the ms clock neatly in terms of the
1ms period and the 16 bit width of the counter. But unless you can alter
the PAD's pulse time plus dead-time so that it's accurately 1/65536 ms,
that's not going to happen.

The difference between us is that I say "measure or look up the minimum
possible time between events and use that number to determine timer
accuracy", whereas John says "Assume that the minimum time between
events is (conveniently) 1/65536ms and take it from there".

As an aside, somewhere else in the thread, John suggested using the
PAD's output to gate a fast clock into the counter. If you do that, you
need to make sure that the fast clock is guaranteed to have exactly one
edge per event. Failure to do so will result in the PAD gating a clock
that's not currently doing anything (missed count) or gating a clock that
may transition more than once during the PAD's output pulse (multiple
counts per event). However, upon re-reading some of the thread, I
realise that John abandoned that idea, so my spiel in my last post about
lost/extra counts is redundant.

Anyway, good luck in building your project, Paul - I hope it's a success.

--
Rick
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Paul Taylor
electronics forum beginner


Joined: 10 Feb 2005
Posts: 45

PostPosted: Fri Jul 21, 2006 8:25 am    Post subject: Re: FREQ COUNTER help Reply with quote

"Rick" <rik_nntp@dsl.pipex.com> wrote in message
news:iqGdnQDDtYFxciLZnZ2dnUVZ8qWdnZ2d@pipex.net...
Quote:
In the case that of a discriminator with
memory and a dead-time, that simplifies to "what's the length of that
memory of an event plus the deadtime", which is what you're now saying.

---
No, it's what _you're_ now saying. I always postulated a train of
maximum-density detectable pulses and you're only now coming around
to it while trying to make it seem like it's been your position all
along.

Trouble is, you define maximum density (see 2 or 3 of your posts ago) in
terms of the 1ms reporting period and in terms of the bit-width of the
counter. Better tell the PAD your assumptions.


--
Rick

Rick 2 to the power of 16 is the maximum counter rate required!
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Paul Taylor
electronics forum beginner


Joined: 10 Feb 2005
Posts: 45

PostPosted: Fri Jul 21, 2006 8:20 am    Post subject: Re: FREQ COUNTER help Reply with quote

<bill.sloman@ieee.org> wrote in message
Quote:
It doesn't need to be synchronous. Only the first stage needs to be able
to start and stop in one cycle. The rest of it can be a ripple counter.
If you wait for things to calm down after the first stage is stopped, the
rippling will finish before you read the counter.

First counter I ever put on a printed circuit board worked that way - a
monstable stopped you reading the counter until the last count had
rippled all the way through. That was back in 1972.

Nowadays that sort of trickery is rarely necessary - though I did
extend an MC100E016 based counter with an 74HCT40103 a few years back
for a particularly cheap-skate customer. It cost more in design time
than it could ever save in parts costs, but it was quite fun to do.

--
Bill Sloman, Nijmegen


That sounded like fun, we have plenty of the cheap skate customer coming
through, wanting something for nothing?
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Michael A. Terrell
electronics forum Guru


Joined: 24 Mar 2005
Posts: 2291

PostPosted: Fri Jul 21, 2006 5:33 am    Post subject: Re: FREQ COUNTER help Reply with quote

bill.sloman@ieee.org wrote:
Quote:

This is "insane" in the Communist Russian sense - if you disagree with
my ideology you must be crazy and I have to lock you up in an insane
asylum until you see the logic of my position.

Try a little reasoned argument the next time you come across a poltical
opinion you don't like. Your education system doesn't exactly prepare
you for this sort of discussion, but it is a skill you ought to learn.

--
Bill Sloman, Nijmegen


It is insane for you to sit on the other side of the world and try to
influence how I think. Maybe you could learn that, if you tried?


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
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Bill Sloman
electronics forum Guru


Joined: 12 May 2005
Posts: 1080

PostPosted: Fri Jul 21, 2006 3:11 am    Post subject: Re: FREQ COUNTER help Reply with quote

Michael A. Terrell wrote:
Quote:
bill.sloman@ieee.org wrote:

John Fields wrote:
On 19 Jul 2006 02:46:44 -0700, bill.sloman@ieee.org wrote:


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.

---
When not having to deal with some of the less-than-human lifeforms
infecting this forum, Phil often comes into his own and offers
outstanding advice, I've found. YMMV.

On his chosen subjects he is pretty good, but he does degenerate into
snarling rage remarkably quickly, and he remains incensed for
remarkably long periods.

--
Bill Sloman, Nijmegen



Kind of like your insane anti America rants, old boy?

This is "insane" in the Communist Russian sense - if you disagree with
my ideology you must be crazy and I have to lock you up in an insane
asylum until you see the logic of my position.

Try a little reasoned argument the next time you come across a poltical
opinion you don't like. Your education system doesn't exactly prepare
you for this sort of discussion, but it is a skill you ought to learn.

--
Bill Sloman, Nijmegen
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Bill Sloman
electronics forum Guru


Joined: 12 May 2005
Posts: 1080

PostPosted: Fri Jul 21, 2006 3:06 am    Post subject: Re: FREQ COUNTER help Reply with quote

Michael A. Terrell wrote:
Quote:
bill.sloman@ieee.org wrote:

Michael A. Terrell wrote:
bill.sloman@ieee.org wrote:

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.


The same could be said for you, Bill.

But I said it first. You have to invent your own abuse if you want to
get any brownie points.

And I don't show much sign of blowing a blood vessel.


I don't want brownie points, Bill. Brownies are young girls on their
way to being Girls Scouts.

The Australian scouting movement uses the same name for that particular
age-group.
The concept has generalised over the years.

Quote:
The first sign of blowing a blood vessel is
when it explodes.

True, but the chances of it blowing depend pretty heavily on your blood
pressure. Mine is about 130/65.

--
Bill Sloman, Nijmegen
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Michael A. Terrell
electronics forum Guru


Joined: 24 Mar 2005
Posts: 2291

PostPosted: Fri Jul 21, 2006 1:29 am    Post subject: Re: FREQ COUNTER help Reply with quote

bill.sloman@ieee.org wrote:
Quote:

John Fields wrote:
On 19 Jul 2006 02:46:44 -0700, bill.sloman@ieee.org wrote:


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.

---
When not having to deal with some of the less-than-human lifeforms
infecting this forum, Phil often comes into his own and offers
outstanding advice, I've found. YMMV.

On his chosen subjects he is pretty good, but he does degenerate into
snarling rage remarkably quickly, and he remains incensed for
remarkably long periods.

--
Bill Sloman, Nijmegen



Kind of like your insane anti America rants, old boy?


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
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Michael A. Terrell
electronics forum Guru


Joined: 24 Mar 2005
Posts: 2291

PostPosted: Fri Jul 21, 2006 1:28 am    Post subject: Re: FREQ COUNTER help Reply with quote

bill.sloman@ieee.org wrote:
Quote:

Michael A. Terrell wrote:
bill.sloman@ieee.org wrote:

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.


The same could be said for you, Bill.

But I said it first. You have to invent your own abuse if you want to
get any brownie points.

And I don't show much sign of blowing a blood vessel.


I don't want brownie points, Bill. Brownies are young girls on their
way to being Girls Scouts. The first sign of blowing a blood vessel is
when it explodes.



--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
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Bill Sloman
electronics forum Guru


Joined: 12 May 2005
Posts: 1080

PostPosted: Thu Jul 20, 2006 11:06 pm    Post subject: Re: FREQ COUNTER help Reply with quote

Michael A. Terrell wrote:
Quote:
bill.sloman@ieee.org wrote:

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.


The same could be said for you, Bill.

But I said it first. You have to invent your own abuse if you want to
get any brownie points.

And I don't show much sign of blowing a blood vessel.

--
Bill Sloman, Nijmegen
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Bill Sloman
electronics forum Guru


Joined: 12 May 2005
Posts: 1080

PostPosted: Thu Jul 20, 2006 11:03 pm    Post subject: Re: FREQ COUNTER help Reply with quote

John Fields wrote:
Quote:
On 19 Jul 2006 02:46:44 -0700, bill.sloman@ieee.org wrote:


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.

---
When not having to deal with some of the less-than-human lifeforms
infecting this forum, Phil often comes into his own and offers
outstanding advice, I've found. YMMV.

On his chosen subjects he is pretty good, but he does degenerate into
snarling rage remarkably quickly, and he remains incensed for
remarkably long periods.

--
Bill Sloman, Nijmegen
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martin griffith
electronics forum Guru


Joined: 06 May 2005
Posts: 1098

PostPosted: Thu Jul 20, 2006 10:11 pm    Post subject: Re: FREQ COUNTER help Reply with quote

On Thu, 20 Jul 2006 21:25:02 GMT, in sci.electronics.design "Michael
A. Terrell" <mike.terrell@earthlink.net> wrote:

Quote:
bill.sloman@ieee.org wrote:

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.


The same could be said for you, Bill.

Phil is fun, his verbal/keyboard skills are somewhat limited when it
comes to adjectives, he does needs some lessons in subtlety, wit and
sarcasm, and Bill seems to know a lot more than me, as does that Jim
dude from Az, and despite significant differences in political
philosophy I'm happy to see what any of them has say about technology.



martin
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John Fields
electronics forum Guru


Joined: 24 Mar 2005
Posts: 3260

PostPosted: Thu Jul 20, 2006 9:29 pm    Post subject: Re: FREQ COUNTER help Reply with quote

On 19 Jul 2006 02:46:44 -0700, bill.sloman@ieee.org wrote:


Quote:
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.

---
When not having to deal with some of the less-than-human lifeforms
infecting this forum, Phil often comes into his own and offers
outstanding advice, I've found. YMMV.


--
John Fields
Professional Circuit Designer
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Michael A. Terrell
electronics forum Guru


Joined: 24 Mar 2005
Posts: 2291

PostPosted: Thu Jul 20, 2006 9:25 pm    Post subject: Re: FREQ COUNTER help Reply with quote

bill.sloman@ieee.org wrote:
Quote:

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.


The same could be said for you, Bill.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
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Rick H
electronics forum beginner


Joined: 19 Jul 2005
Posts: 18

PostPosted: Thu Jul 20, 2006 9:14 pm    Post subject: Re: FREQ COUNTER help Reply with quote

John Fields wrote:

Quote:
On Thu, 20 Jul 2006 07:53:47 GMT, rick H <rik_nntp@dsl.pipex.com
wrote:

John Fields <jfields@austininstruments.com> wrote:

What you obviously missed is that the PAD issues output pulses of
identical widths for _any_ detected event and, then, when that event
dies away and there's time for the system to recover, another hit
can be detected.

That output pulsewidth added to the recovery time of the system
exquisitely defines its throughput, regardless of the spacing or
coincidence of the input photons.


You've changed your argument - I originally said that two closely-spaced
events (I just made the numbers up as an example)

---
My argument hasn't changed at all; I posited a chain of equidistant
pulses, which is the best the system can do, and you objected with
your ridiculous "bursty" hypothesis. Ridiculous because it's
certainly possible for the PMT to be hit with 100 photons in a
nanosecond, but there's no way it could resolve the hits as distinct
events.

So a scenario that the detector can't deal with is ridiculous, rather than,
say, a failure of the detector or counter to be able to count all the
events you might like it to count.

Let's remind ourselves exactly what your "maximum throughput" pulses look
like, as described a couple of posts ago: "65536 pluses were spaced
equidistantly in a window 1.0 pulse or minus something millie seconds
wide."
You've imposed a requirement on the PAD to spurt out pulses exactly every
1/65535ms. I don't think it will be that accommodating. If the pulses are
shorter and you're still sampling at 1/65536 ms, you'll fail to detect some
pulses. If the pulses are longer, you'll sometimes double-clock on a
single event pulse. Both scenarios give you a miscount.
In fact, the only way to get it right is to make sure that the clock you're
gating is going to transition EVERY time the PAD happens to pulse. If that
means sampling more often than 1/65536ms and that the counter MAY overflow
in any given ms, then so be it. If that means sampling less frequently
than 1/65536ms and that the counter WILL NEVER overflow in any ms period,
then so be it. The point being, of course, that you must adjust your clock
to the maximum event rate, not hope that the maximum event rate just
happens to be related to your clock's bit-width and the reporting interval.
Accounting for the maximum event rate (albeit the maximum at the PAD
output, which I hadn't reckoned with before) is what I've being saying all
along.


Quote:
---

defined the ppm accuracy required of the ms timer to produce +/- 1
event accuracy per ms "time bin".
You started arguing that you'd assumed they were equally
spaced, but now you're saying that it's the width of the pulses from
this PAD gizmo (plus the dead time) which count - which is certainly true.

---
Yes, and my original pulse train was just that; a series of pulses
with widths and spacing which will allow the system to achieve its
maximum throughput.
---

Given that you know that the PAD spurts out specific pulse widths rather
than impulses, why did you suggests this "smearing" approach elsewhere?

---
I considered using the input to the PAD (the output of the PMT) as a
gate to allow a counter to accumulate fast clocks during the length
of the input, the rationale being that multiple hits would create a
wider output from the PMT. However, I found that wasn't necessarily
true and was a bad idea. That's why I replied to the op's request
for an explanation with : "I was thinking of something else."

Fair enough.

Quote:
---

It's
already done by the PAD. I suppose you could further smear the pulse to
the end of the recovery time, but any more than that and you'll miss the
next detectable event - you'll increase the dead-time.

---
You seem to have a remarkable grasp of the obvious.
---

Given that you know the that PAD output's pulsewidth is "equisitely
defined", why guess at 10ppm accuracy on the timer? The accuracy can be
deduced from the ratio the pulsewidth+dead-time to the ms period.

---
Who guessed? Initially all there was to work with was the OP's
65536 pulses which he wanted to stuff into a millisecond,

Nope. 65536 comes from the maximum count from the counter (which is
presumably 65535), it does not come from the period of the pulses from the
PAD. If you hypothesise 1/65536ms pulses in order to determine the ppm
accuracy of the ms clock required for 1 event accuracy, you've blown it,
because the actual maximum rate from the PAD may be slower (in which case
your tolerance is too tight, but obviously that's okay) or faster (in which
case your tolerance isn't tight enough).

Quote:
yielding a
period of about 1.53E-8s. That's 15.3ns, and
since there are one million nanoseconds in a millisecond,

what was that about me stating the obvious!?

Quote:
one pulse period would be 15.3
parts per million. So, in order not to miss a pulse or count an
extra pulse, the window would have to be one millisecond long with a
tolerance of less than +/- 15.3 ppm. Something like 10ppm, just for
grins.
---

I guess I should originally have been more thorough and said that you
need to know the minimum time interval between events *that the
detector can distinguish and hence that the counter can count* in order
to determine the ppm accuracy.

---
More thorough and less caustic would have been nice.

Caustic replies emerge from being called an a*****le. Being English, I prefer
the term "arsehole".


Quote:
---

In the case that of a discriminator with
memory and a dead-time, that simplifies to "what's the length of that
memory of an event plus the deadtime", which is what you're now saying.

---
No, it's what _you're_ now saying. I always postulated a train of
maximum-density detectable pulses and you're only now coming around
to it while trying to make it seem like it's been your position all
along.

Trouble is, you define maximum density (see 2 or 3 of your posts ago) in
terms of the 1ms reporting period and in terms of the bit-width of the
counter. Better tell the PAD your assumptions.


--
Rick
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Bill Sloman
electronics forum Guru


Joined: 12 May 2005
Posts: 1080

PostPosted: Thu Jul 20, 2006 5:32 pm    Post subject: Re: FREQ COUNTER help Reply with quote

Ken Smith wrote:
Quote:
In article <1153139085.236239.262300@35g2000cwc.googlegroups.com>,
bill.sloman@ieee.org> wrote:

Paul Taylor wrote:
Hi i am presently trying to build a counter that counts freq upto 65536 Khz
in less than 1 msec is this possible also has any one any ideas to where i
should start thanks in advance for your help.

Obviously enugh, a counter driven at 65536kHz - I presume you mean
65.536MHz - will accumulate 65536 counts in one millisecond.

If he doesn't, there is the option of a frequency multiplying PLL to
consider.

A 16-bit wide synchronous counter capable of running at 66MHz isn't
entirely trivial.

It doesn't need to be synchronous. Only the first stage needs to be able
to start and stop in one cycle. The rest of it can be a ripple counter.
If you wait for things to calm down after the first stage is stopped, the
rippling will finish before you read the counter.

First counter I ever put on a printed circuit board worked that way - a
monstable stopped you reading the counter until the last count had
rippled all the way through. That was back in 1972.

Nowadays that sort of trickery is rarely necessary - though I did
extend an MC100E016 based counter with an 74HCT40103 a few years back
for a particularly cheap-skate customer. It cost more in design time
than it could ever save in parts costs, but it was quite fun to do.

--
Bill Sloman, Nijmegen
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