magnetic field

[Bob Myers]

"John E. Hadstate" <jh113355@hotmail.com> wrote in message
news:0uy2h.19177$Fd7.15881@bignews6.bellsouth.net...

Depends on what you mean by signal. (This conversation is becoming
downright Clintonesque.)

Well, THAT would depend on just what your definition
of "is" is....

But I think at this point we ARE in violent agreement about
pretty much all the real points, and are in danger of starting
a task of rearranging the semantic deck chairs, so I
think I'll quit until something else comes along.

Elsewhere I have given an example
of a signal which cannot be unambiguously classified as
either "analog" or "digital" in the common (and sloppy)
use of those terms merely by looking at it.

I read it. I thought it was brilliant.

Thanks!

Bob M.

 

[Homer J Simpson]

"CCE" <cenglish@snapsinc.com> wrote in message
news:1162519333.757065.200490@m73g2000cwd.googlegroups.com...

How many different heights?

Two or three. The cycle time would be less than one minute. This is not
an application that would run continuously either.

Just use limit switches then. Enable the right limit switch as needed. It'll
be a lot more accurate and repeatable.



--
++++++++++++++++++++++++++++++++++++++++++++++++++++
+ Required crap appended to avoid restrictions imposed by brain +
+ damaged idiots.
+
+ Server Response: '441 Posting Failed (Rejected by POST filter)', +
+ Port: 119, Secure(SSL): No, Server Error: 441,
+
+ Error Number: 0x800CCCA9
+
++++++++++++++++++++++++++++++++++++++++++++++++++++

 

[Wim Lewis]

In article <1162490145.877448.8540@b28g2000cwb.googlegroups.com>,
CCE <cenglish@snapsinc.com> wrote:

I'm looking for some advice on a motor application. To keep it
simple, I'll use the following description. I have a 20 lb weight
that I want to raise and lower according to a time schedule. [....]
I want to use a PLC to control the system. The speed of the application
is relatively slow. Let's say it takes 1 second to raise or lower
the weight 12 inches. Since I need to hold the weight for a few
seconds, I'm thinking I need a stepper motor.

If you use a worm-gear gearbox, you can arrange it so that the weight
cannot drive the motor shaft, but the motor can easily drive the weight.
(This seems counterintuitive to me, but it works.) That would greatly
simplify holding the weight --- just shut off the motor, which could
then be a simple dc type.

Raising 20 lb at 12 in/sec is about 30 watts before you take any
inefficiencies into account.

--
Wim Lewis <wiml@hhhh.org>, Seattle, WA, USA. PGP keyID 27F772C1

 

[Ray Andraka]

Jerry Avins wrote:

Ray Andraka wrote:

Jerry Avins wrote:


Sure. You may think of a one-shot as a digital device, but it takes a
fair amount of analog savvy to build one whose pulse width is
independent of duty cycle.


As a digital guy, I sure don't consider one-shots digital. By
one-shots, I am referring to those devices that use the physical
characteristics of components (typically capacitance and resistance)
to set a time delay.

The distinction I use in my book (which sadly will probably never be
finished because of the time involved writing it) is that an analog
circuit depends on the physical properties of the components of the
circuit as an integral part of the processing. A digital circuit
processes the signal through a logical or numerical manipulation of
the signal so that the circuit itself is only incidental to the
processing.

Clearly, with that definition, one-shots such as the 74123 belong to
the class of analog circuits regardless of whether they were offered
as a component within a digital logic family. The only thing digital
about these parts is the logic family compatible I/O and the simple
logic controls built in to allow the one shot to be operated by and
output to the logic family.

Another circuit that used to be commonly used with digital logic that
is really an analog part is the delay line.


I'd say that a one-shot is digital in intent and analog in execution. I
believe that's true of any physical digital component, just more clearly
evident with circuits that intentionally use Rs and Cs for timing. All
circuits incorporate Rs and Cs, whether intentionally or not. Memory
buses are "digital" too, but modern clock speeds dictate that they be
designed like the broadband transmission lines they really are.

Very few dichotomies are entirely clear. For most, it is possible to
assign most items to one class or the other although the matter is
ambiguous for some near the division. The analog-digital dichotomy puts
the fuzzy dividing line over near one edge. We may use current,
pressure, voltage, fluid flow and other analogs to represent ones and
zeros, but they are all analogs nonetheless. Those ones and zeros exist
in pure form only in out minds. Even marks on paper are analogs of a
sort. We move the division to match a particular purpose. Assuming that
it is fixed hobbles our thoughts.

I began this thread to isolate this discussion from the rancor
developing in another one. I'm pleased to note that it seems to have
succeeded.

Jerry

Ah, but Jerry, I think perhaps you missed the distinction. The one-shot
depends on the properties of the R's and C's to set up the timing
parameter. In essence, the one shot is comparing a decaying analog
voltage against a reference analog voltage and outputting a digital
signal to indicate whether or not the reference threshold has been
crossed. There is clearly an analog component to this circuit that
would not work the same if the values of the components were changed.

Memory, and other digital circuits that incorporate capacitors and
resistors do not depend on the values of those components to set the
behavior of the circuit. The digital realization could be moved to
another logic foundation (say hydraulics) and it would perform the same
function (albiet, maybe not as fast). The analog circuit however
depends on the characteristics of the components, so moving it to
another technology generally means either finding a component with
equivalent characteristics or modeling the behavior of the replaced
component with something else that mimics the physical characteristics
of the component. See the fundamental difference is the digital is
performing a numerical or logical manipulation of the signal where the
analog is modifying the signal by subjecting it to physical properties
of the materials, which generally is not quantized.

Digital, by design quantizes the analog nature of the underlying
circuit to represent numbers, but fundamentally you are doing numerical
operations rather than relying on the physical properties of a component
to do the processing (decay of a voltage, for example).

 

[Jerry Avins]

Ray Andraka wrote:

Jerry Avins wrote:

Ray Andraka wrote:

Jerry Avins wrote:


Sure. You may think of a one-shot as a digital device, but it takes
a fair amount of analog savvy to build one whose pulse width is
independent of duty cycle.


As a digital guy, I sure don't consider one-shots digital. By
one-shots, I am referring to those devices that use the physical
characteristics of components (typically capacitance and resistance)
to set a time delay.

The distinction I use in my book (which sadly will probably never be
finished because of the time involved writing it) is that an analog
circuit depends on the physical properties of the components of the
circuit as an integral part of the processing. A digital circuit
processes the signal through a logical or numerical manipulation of
the signal so that the circuit itself is only incidental to the
processing.

Clearly, with that definition, one-shots such as the 74123 belong to
the class of analog circuits regardless of whether they were offered
as a component within a digital logic family. The only thing digital
about these parts is the logic family compatible I/O and the simple
logic controls built in to allow the one shot to be operated by and
output to the logic family.

Another circuit that used to be commonly used with digital logic that
is really an analog part is the delay line.


I'd say that a one-shot is digital in intent and analog in execution.
I believe that's true of any physical digital component, just more
clearly evident with circuits that intentionally use Rs and Cs for
timing. All circuits incorporate Rs and Cs, whether intentionally or
not. Memory buses are "digital" too, but modern clock speeds dictate
that they be designed like the broadband transmission lines they
really are.

Very few dichotomies are entirely clear. For most, it is possible to
assign most items to one class or the other although the matter is
ambiguous for some near the division. The analog-digital dichotomy
puts the fuzzy dividing line over near one edge. We may use current,
pressure, voltage, fluid flow and other analogs to represent ones and
zeros, but they are all analogs nonetheless. Those ones and zeros
exist in pure form only in out minds. Even marks on paper are analogs
of a sort. We move the division to match a particular purpose.
Assuming that it is fixed hobbles our thoughts.

I began this thread to isolate this discussion from the rancor
developing in another one. I'm pleased to note that it seems to have
succeeded.

Jerry

Ah, but Jerry, I think perhaps you missed the distinction. The one-shot
depends on the properties of the R's and C's to set up the timing
parameter. In essence, the one shot is comparing a decaying analog
voltage against a reference analog voltage and outputting a digital
signal to indicate whether or not the reference threshold has been
crossed. There is clearly an analog component to this circuit that
would not work the same if the values of the components were changed.

Memory, and other digital circuits that incorporate capacitors and
resistors do not depend on the values of those components to set the
behavior of the circuit. The digital realization could be moved to
another logic foundation (say hydraulics) and it would perform the same
function (albiet, maybe not as fast). The analog circuit however
depends on the characteristics of the components, so moving it to
another technology generally means either finding a component with
equivalent characteristics or modeling the behavior of the replaced
component with something else that mimics the physical characteristics
of the component. See the fundamental difference is the digital is
performing a numerical or logical manipulation of the signal where the
analog is modifying the signal by subjecting it to physical properties
of the materials, which generally is not quantized.

Digital, by design quantizes the analog nature of the underlying
circuit to represent numbers, but fundamentally you are doing numerical
operations rather than relying on the physical properties of a component
to do the processing (decay of a voltage, for example).

I wasn't thinking of the memory chips themselves, with charges on
capacitors standing in for ones and zeros, but rather the analog nature
of the interconnections, with their transmission delays, characteristic
impedances, and matched terminations. A flip-flop' set-up and hold times
arise from the underlying analog nature of its components. Even the
pulse width of the one-shot is quantized in trinary a way: long enough,
OK, and too short. Otherwise, they wouldn't be useful. (The memory
chip's charges are similarly quantized: in the zero range, trouble, and
in the one range.) I don't see the distinction between a digital and an
analog circuit element as fundamentally more meaningful than the
distinction between a digital and an analog wire.

Jerry
--
"I view the progress of science as ... the slow erosion of the
tendency to dichotomize." Barbara Smuts, U. Mich.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ

 

[Ray Andraka]

Jerry Avins wrote:

I wasn't thinking of the memory chips themselves, with charges on
capacitors standing in for ones and zeros, but rather the analog nature
of the interconnections, with their transmission delays, characteristic
impedances, and matched terminations. A flip-flop' set-up and hold times
arise from the underlying analog nature of its components. Even the
pulse width of the one-shot is quantized in trinary a way: long enough,
OK, and too short. Otherwise, they wouldn't be useful. (The memory
chip's charges are similarly quantized: in the zero range, trouble, and
in the one range.) I don't see the distinction between a digital and an
analog circuit element as fundamentally more meaningful than the
distinction between a digital and an analog wire.

Jerry

Yes, I agree that board designers need to take into account the analog
nature of the signal transmission, and I don't think any current media
for digital logic is wholly digital. That said, I guess I am looking at
it from an algorithmic point of view while you are looking at it from a
physical point of view. To me, digital basically means that your
circuit is using numeric methods rather than physical properties to
obtain the desired result.

Granted, you will have to take into account analog effects in doing a
complete digital implementation, but not for the digital algorithm
itself to work. The distinction is that for a digital circuit any
analog behavior is not germane to the algorithm, rather it exists (often
as a hinderance) as an artifact of the implementation. Contrast that
with an analog circuit where those device physical properties are a
necessary ingredient to a functioning design because you are exploiting
those properties to perform the signal processing.

 

[glen herrmannsfeldt]

Jerry Avins wrote:

It seems to me important to agree on criteria for deciding whether a
particular circuit or signal is digital or analog

One criterion is intended use; there seems to be general agreement about
that, so I don't address it here. Another criterion is the nature if the
signal or circuit itself, without reference to intentions. That is the
topic of this short essay.

I knew someone once who built a low power FM transmitter.
The final output was a 74S04 TTL gate, cheaper than other
100MHz transistors, and works fine in analog mode.

-- glen

 

[glen herrmannsfeldt]

Jerry Avins wrote:

(snip on open and closed relay contacts)

You could say the same about a door, but degree matters, especially to
the obese.

This reminds me of a discussion about how switch (and relay)
contacts usually have some oxide that the electrons have to
tunnel through. There really isn't metal to metal contact.
(Maybe only one atomic layer of oxide, though.)

-- glen

 

[glen herrmannsfeldt]

Ray Andraka wrote:

(snip)

Ah, but Jerry, I think perhaps you missed the distinction. The one-shot
depends on the properties of the R's and C's to set up the timing
parameter. In essence, the one shot is comparing a decaying analog
voltage against a reference analog voltage and outputting a digital
signal to indicate whether or not the reference threshold has been
crossed. There is clearly an analog component to this circuit that
would not work the same if the values of the components were changed.

One shots usually have both digital and analog circuitry.
Flip-flops and voltage comparators are both important.

Memory, and other digital circuits that incorporate capacitors and
resistors do not depend on the values of those components to set the
behavior of the circuit. The digital realization could be moved to
another logic foundation (say hydraulics) and it would perform the same
function (albiet, maybe not as fast). The analog circuit however
depends on the characteristics of the components, so moving it to
another technology generally means either finding a component with
equivalent characteristics or modeling the behavior of the replaced
component with something else that mimics the physical characteristics
of the component.

In real life it gets worse. Besides DRAM, digital systems have used
analog circuitry for a long time. Pass transistors for one example.
There are stories of Cray using long winding PC board paths to delay
signals enough to arrive at the right time. Intel processors
traditionally (at least the 8080 and 8086) have used dynamic logic,
such that they won't run below some clock rate.

See the fundamental difference is the digital is
performing a numerical or logical manipulation of the signal where the
analog is modifying the signal by subjecting it to physical properties
of the materials, which generally is not quantized.

Digital, by design quantizes the analog nature of the underlying
circuit to represent numbers, but fundamentally you are doing numerical
operations rather than relying on the physical properties of a component
to do the processing (decay of a voltage, for example).

So DRAM is analog?

-- glen

 

[Steve Underwood]

glen herrmannsfeldt wrote:

Jerry Avins wrote:

(snip on open and closed relay contacts)

You could say the same about a door, but degree matters, especially to
the obese.


This reminds me of a discussion about how switch (and relay)
contacts usually have some oxide that the electrons have to
tunnel through. There really isn't metal to metal contact.
(Maybe only one atomic layer of oxide, though.)

-- glen

I've had corroded switch contacts make a pretty good copper oxide

rectifier.

Steve

 

[Howard Eisenhauer]

On Fri, 03 Nov 2006 21:07:10 -0800, glen herrmannsfeldt
<gah@ugcs.caltech.edu> wrote:

Jerry Avins wrote:

It seems to me important to agree on criteria for deciding whether a
particular circuit or signal is digital or analog

One criterion is intended use; there seems to be general agreement about
that, so I don't address it here. Another criterion is the nature if the
signal or circuit itself, without reference to intentions. That is the
topic of this short essay.

I knew someone once who built a low power FM transmitter.
The final output was a 74S04 TTL gate, cheaper than other
100MHz transistors, and works fine in analog mode.

-- glen

I once used a TTL NOR gate as a mixer- worked very well.

Worked so well in fact that not only did I get A+B & A-B outputs I
also got A, B, 2A+B, 2A-B, A+2B, A-2B, 2A+2B, 2A-2B & lottsa various
other stuff .

H.

 

[Jerry Avins]

Ray Andraka wrote:

Jerry Avins wrote:


I wasn't thinking of the memory chips themselves, with charges on
capacitors standing in for ones and zeros, but rather the analog
nature of the interconnections, with their transmission delays,
characteristic impedances, and matched terminations. A flip-flop'
set-up and hold times arise from the underlying analog nature of its
components. Even the pulse width of the one-shot is quantized in
trinary a way: long enough, OK, and too short. Otherwise, they
wouldn't be useful. (The memory chip's charges are similarly
quantized: in the zero range, trouble, and in the one range.) I don't
see the distinction between a digital and an analog circuit element as
fundamentally more meaningful than the distinction between a digital
and an analog wire.

Jerry

Yes, I agree that board designers need to take into account the analog
nature of the signal transmission, and I don't think any current media
for digital logic is wholly digital. That said, I guess I am looking at
it from an algorithmic point of view while you are looking at it from a
physical point of view. To me, digital basically means that your
circuit is using numeric methods rather than physical properties to
obtain the desired result.

Granted, you will have to take into account analog effects in doing a
complete digital implementation, but not for the digital algorithm
itself to work. The distinction is that for a digital circuit any
analog behavior is not germane to the algorithm, rather it exists (often
as a hinderance) as an artifact of the implementation. Contrast that
with an analog circuit where those device physical properties are a
necessary ingredient to a functioning design because you are exploiting
those properties to perform the signal processing.

Calling circuits, signals, and systems "digital" is certainly useful
(and I'll keep doing it), but (I think you agree) it describes their use
and design, not their physical nature. I think keeping that distinction
helps me to maintain insight and to remember that technology isn't magic.

A lady brought an old photo of her deceased husband to a photography
studio. She wanted it enlarged and was told that it was no problem.
(Good scanners are cheap nowadays.) She asked if the hat could be
removed, and was told that it would be more difficult, hence expensive.
(Digital photography has made this work wonderfully easy, but only by
comparison.) The photographer then asked what color her husband's hair
had been and which side it had been parted on. "What kind of question is
that?" she asked. "When you take the hat off, you'll know."

Jerry
--
"I view the progress of science as ... the slow erosion of the
tendency to dichotomize." Barbara Smuts, U. Mich.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ

 

[Michael A. Terrell]

glen herrmannsfeldt wrote:

So DRAM is analog?

Its all done with smoke and capacitors.


--
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

 

[Steve Underwood]

Michael A. Terrell wrote:

glen herrmannsfeldt wrote:

So DRAM is analog?



Its all done with smoke and capacitors.

They only smoke when overclocked.

Steve

 

[Michael A. Terrell]

Steve Underwood wrote:

Michael A. Terrell wrote:
glen herrmannsfeldt wrote:

So DRAM is analog?



Its all done with smoke and capacitors.

They only smoke when overclocked.

Steve

Or if they don't like the electrons you feed them.


--
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

 

[Ray Andraka]

Its all done with smoke and capacitors.


They only smoke when overclocked.

Naw, it's just you only see the smoke when you do something that lets
the magic smoke out of the package. It's sort of like a genie, once you
let the smoke out, the magic is gone and the part no longer functions.

 

[Ron N.]

Jerry Avins wrote:

It seems to me important to agree on criteria for deciding whether a
particular circuit or signal is digital or analog

At the quantum level, everything might be digital; but above that
level everything looks more analog. However many digital engineers
will only treat anything as analog when dragged kicking and
screaming.

Otherwise, if there exist a useful model of a signal or circuit
which can treat everything as a bunch of "1"'s or "0"'s, and still
predict the systems behavior correctly (within the applications
reliability targets, and when the system is operated within design
contraints), then any of the actual behavior outside of the digital
models is ignored.

So the difference between digital and analog is conscious
ignorance. If the ignorance succeeds, then the circuit or
signal is digital. If there is a failure of this ignorance,
or the system is being operated near the edge of operating
constraints or reliability goals, then analog models are brought
back into the picture to see if they can do better.


IMHO. YMMV.
--
rhn A.T nicholson d.0.t C-o-M

 

[Jerry Avins]

Ron N. wrote:

...

So the difference between digital and analog is conscious
ignorance. If the ignorance succeeds, then the circuit or
signal is digital. If there is a failure of this ignorance,
or the system is being operated near the edge of operating
constraints or reliability goals, then analog models are brought
back into the picture to see if they can do better.

That seems very cogent to me. Thanks.

Jerry
--
"I view the progress of science as ... the slow erosion of the
tendency to dichotomize." Barbara Smuts, U. Mich.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ

 

[Richard Owlett]

Jerry Avins wrote:

Ron N. wrote:

...

So the difference between digital and analog is conscious
ignorance. If the ignorance succeeds, then the circuit or
signal is digital. If there is a failure of this ignorance,
or the system is being operated near the edge of operating
constraints or reliability goals, then analog models are brought
back into the picture to see if they can do better.


That seems very cogent to me. Thanks.

Jerry

May I give a "counter example"?

Light was once thought to be "continuous" ("analog").
*THEN* photons were "discovered". Particles are "discrete"/"digital".

Please note liberal use of " character.


In other words (as has been stated before), chose the representation
most appropriate to problem.

 

[Zak]

Steve Underwood wrote:

If there was a choice you'd use a proper op-amp. You only use these
gates because they are leftovers in a multi-gate package. 74xx devices
were used quite often in semi-analogue roles.

Did anyone ever analyse or even draw a schematic of the 'keychain
whistle' devices? When you'd whithle, it would beep back at you to
indicate where it was.

ISTR it used a CD4000 or similar as only active device, and a single
piezo as both mic and beeper.

It would go quite some time on a battery as well. Clever design.



Thomas