[time-nuts] Control Systems (was: uC ADC resolution)

Attila Kinali attila at kinali.ch
Sun Jun 11 15:22:14 EDT 2017

On Sun, 11 Jun 2017 11:21:15 -0700
Chris Albertson <albertson.chris at gmail.com> wrote:

> This has been my opinion for a LONG time.  It is easy to come up with good
> solutions if to just throw money at the problem.    So you see here people
> proposing just going top of the line all across but an engineer earns his
> money
> by comping up with cost effective solutions that meet all the stated
> requirements.

Yes, I have done plenty of that. If the production run will be >100k
then it's well worth spending a month or two to shave off 1€.
But on a small volume project, or even worse a one-off project,
I am not going to try save 10€ if I that would cost me a day of reading
and doing calculations.

> So you understand my questions are all like this:  "If you back down from
> top of the line solution how does that effect real world performance?"
> No one answers.

Because there are no easy answers. What you are asking requires
someone sitting down and do the math (or simulations) and figure
out what the limiting parameters are, when restricting the design
in this or that way.

To give this a little perspective:
For one of my many side-projects, I do need an DAC with a very
high resolution (>23bit). It took me a few days to figure out that I
really need this resolution and cannot do with anything lower. I have
probably poured another 3-4 (man)weeks just calculating and simulating
different designs that looked promising enough to deliver the needed
performance. I have settled on two designs I want to try, but I am
still reading up on different issues and refining the design for those.
I guess it will take me another (man)month or two until I a can say
with confidence that the design is good, will with high probability
deliver the performance I need and there are no easy ways to improve it.
And then I will start the implementation (ie schematics, layout and software).

Like you asked for your temperature control loop, I could have asked
how to build such a DAC. But I would not have gotten any answer.
Because there simply isn't anyone who knows the answer. At least not for
a design with my constraints. If you read carefully what I have asked
on time-nuts and volt-nuts in the last half year or year, you will find
quite a few of my questions relate to this project in some way or other.
Questions on how to do this or that. Questions on whether X is possible
or not and if yes, under what conditions. To some questions I got answers,
to others I didn't. If I didn't get an answer, I knew that the question
is difficult and tried to read up on it as much as I could manage.

I do not know, whether it does look like answering questions on time-nuts
is easy. At least for me it isn't. I came here 10 or 11 years ago.
For over a year I didn't write anything, but just read. Then I ventured
my opinion on things I thought I knew and started asking small questions
here and there (if you want to have some fun, go back and read what I
wrote 8-9 years ago... I was sooo naive...). In the meantime I continued
reading up on different things as time allowed. It really took me full
10 years to reach the level I am at now, but I still do not know anything.
My knowledge is full of holes and things I think I understood but didn't
(the construction of the E1938 is a nice recent example of that). There
are whole areas I have no clue about at all (e.g. how to build low noise
oscillators, or how ADEV, MDEV & co actually work) and I know it will take
me years to gain a sufficient understanding of those. Answering, even simple
questions, can take me easily half an hour. I often have to go back to my
documents and paper collection to check things, as I am unable to remember
everything in detail. Then writing a (hopefully) intelligeble answer is
also something that shouldn't be underestimated.

Hmm.. this ended being up longer than I intended it to be. Sorry about that.
But I hope I made my point clear. If not:

TL;DR: Some questions are just difficult and need someone to sit down
and think hard before they can be answered.

			Attila Kinali
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
                 -- Miss Matheson, The Diamond Age, Neil Stephenson

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