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Home » CadSoft Support Forums » eagle.userchat.eng » Hard Lessons Learned (watch out for land mines)
Hard Lessons Learned (watch out for land mines) [message #163615] Thu, 08 October 2015 19:59 Go to next message
Steve Owens
Messages: 1
Registered: October 2015
Junior Member
So here is my experience with Eaglesoft and Element14 so far and some
land mines you may encounter and how to avoid them.  First of all, the
libraries that are provided with the software should be immediately
discarded.  Don't keep any of them, since you will either end up
designing boards that use over priced parts or parts that Element 14
does not have.  Expecially avoid any parts by Farnell, since they don't
sell their parts cheap nor do their libraries contain parts that they
actually sell.

You are better off discarding their libraries and developing your own. 
It is not hard to make a part in Eagle cad and if you source your parts
and make the designs yourself you won't be disappointed by the
irresponsible curation of non existent parts in the default libraries.

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Re: Hard Lessons Learned (watch out for land mines) [message #163616 is a reply to message #163615] Thu, 08 October 2015 20:19 Go to previous messageGo to next message
shabaz
Messages: 190
Registered: October 2012
Senior Member
> Steve Owens wrote:
>
>
>
> nor do their libraries contain parts that they actually sell
I think one should design a circuit based on the most appropriate
components (appropriate for the design) that one can source.
Requirements include availability, cost, performance, the ability to
second-source, and so on.
If you are designing a circuit based on whatever you can find in a CAD
software library then this is not typically how the design process
works.

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Re: Hard Lessons Learned (watch out for land mines) [message #163621 is a reply to message #163616] Fri, 09 October 2015 10:53 Go to previous messageGo to next message
Guillaume barrey[1]
Messages: 260
Registered: July 2013
Senior Member
I never use Eagle library, at least without editing . Years ago I used
to copy a device from Eagle lib, then checked and edit  the copy. But
today I prefer create build the device from scratch, or by using
packaged from my own library...

But when I create a new board, I always check is all the part I use is
available ! even if I use a part from my own library ! Why ?
- a part use in an previous design can be now 'obsolete' or at least
'not recommended for new design!'
- A capacitor used 5 years ago could now exist in a smaller form factor.
- ....

So Yes, I always check availability, price, obsolescence  .... it's part
of the job !

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Re: Hard Lessons Learned (watch out for land mines) [message #163623 is a reply to message #163616] Fri, 09 October 2015 19:23 Go to previous messageGo to next message
Mark Archibald
Messages: 3
Registered: October 2015
Junior Member
To address Steve's point, I would argue that the hallmark of a useful
library be that it contains parts that are readily available, at
reasonable cost, with good perfomance, and have second sources?

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Re: Hard Lessons Learned (watch out for land mines) [message #163626 is a reply to message #163623] Fri, 09 October 2015 23:28 Go to previous messageGo to next message
shabaz
Messages: 190
Registered: October 2012
Senior Member
Hi Mark,

There is no interface in EAGLE between a library and inventory/stock
levels at distributors, so there can be no assurance that a part in a
library is readily available, nor of good performance.
There have been cases where manufacturers have rapidly deprecated a
product (e.g. CC3000 comes to mind, within the space of just a couple of
years) and the replacements are not pin-compatible.

No-one likes functionality to be removed in later releases of software,
so I think it is right that libraries do not have content deleted over
time to match the state of affairs with manufacturer supply and demand.

I know some people believe EAGLE libraries to be like a menu in a
restaurant, but it is not the same; disappointment if they saw
cheesecake on the menu and it had run out is not comparable to
a CAD package's library.

Just as importantly, there is a trust issue - no-one would invest time
and money building a prototype based on unverified parts libraries. A
project I'm working on is getting ready for parts purchase
(perhaps 500 parts per board)  and I will look very silly in front of my
colleagues if the parts are not available because I didn't check, or if
they do not fit because I didn't verify the landing pattern.
Basically similar to 'don't outsource what is strategic' I guess.


The solution is to create or verify parts libraries. And the process is
established and works - as an example in over 100 boards I've created,
while mistakes have been made, I don't think I've ever had a
landing pattern issue on a prototype that could not be corrected without
more than a couple of wire links on the first prototype. Basically, 'get
it right first time' is the motto, just as relevant for
business and for hobbyists because none of us have time to waste
re-ordering boards. As a quick visible example, one of my published
projects in a blog post has 92 parts on it (and the schematic and
board were entered in EAGLE) - not a huge amount of parts, but not
insignificant either - and the first board worked first time, no need
for a second revision.

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Re: Hard Lessons Learned (watch out for land mines) [message #163666 is a reply to message #163626] Tue, 13 October 2015 15:57 Go to previous messageGo to next message
Mark Archibald
Messages: 3
Registered: October 2015
Junior Member
So, is it fair to say then that you agree that a useful library does
contain parts that are readily available, at reasonoable cost, with good
perfromance, and have second sources.  What I read in your response is
that to achieve these objectives one has to carry out due diligence and
not blindly rely on pre-packaged libraries; is that a fair
intrepretation?

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Re: Hard Lessons Learned (watch out for land mines) [message #163667 is a reply to message #163666] Tue, 13 October 2015 17:51 Go to previous messageGo to next message
shabaz
Messages: 190
Registered: October 2012
Senior Member
Hi Mark!

I'm saying one usually chooses the best parts for the task  (taking into
account cost, performance, availability decisions), and then finding and
verify a library part, or designing your own.

The libraries that were created in EAGLE, were possibly "useful" parts
at one time or another. Should they be deprecated and removed now that
they are "useless" in the eyes of some? I think no, for the reasons
mentioned in the last post.
Besides, some parts like TBA820M are considered useful (and available)
in some parts of the world, but are definitely not suitable for designs
in other parts of the world.

What is useful to us may be useless to others and vice versa. But yes,
one key point is that you wouldn't know it was useful until you'd
verified all parts you need to use yourself.
Some parts libraries attempt to get around this issue by having users
'rate' the part.. so people get visibility of a statistical confidence
of sorts.. much like an Amazon book rating or 'look inside'. It doesn't
guarantee the book is useful, but provides some confidence.

As another real-world example: I have a great (to me) toroid library,
and it was built using custom software that I have tweaked over the
years.
I can design parts like this, and it even tells me exactly where each
wire turn should sit:
[toroid-land.jpg]

But, wound toroids are somewhat esoteric, expensive and unobtainable
unless you contract with a manufacturer to custom-wind them for you (or
carefully hand-wind for half an hour).
That library is useless to most people, extremely useful to me.

What perhaps the original poster's real issue boils down to (I'm
guessing), is that some people need a hand to realise what are "popular"
or "jelly-bean" parts that will usually be in stock, have reasonable
performance,
and are likely to still be available from suppliers when they actually
make use of the library. If users know that, then they can have some
confidence that a library contains the part, the library
part has been sufficiently debugged through popular use, and the
distributor's inventory contains the part.

An approach sometimes seen is a 'jelly-bean' library, or perhaps some
parts list marked as 'jelly-bean'; companies like Adafruit and Dangerous
Prototypes have libraries that are kind-of like this, already available
for EAGLE.
(Called generic parts libraries or similar I think). They probably are
fine, but personally I would check each part myself, no matter the
rating.

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Re: Hard Lessons Learned (watch out for land mines) [message #163670 is a reply to message #163667] Wed, 14 October 2015 09:58 Go to previous messageGo to next message
Friedrich Bleikamp
Messages: 89
Registered: August 2005
Member
Am 13.10.2015 um 19:51 schrieb shabaz:
> Hi Mark!
>
> I'm saying one usually chooses the best parts for the task (taking into
> account cost, performance, availability decisions), and then finding and
> verify a library part, or designing your own.
>

In the company in which I worked before my retirement, every
component has been managed by a unique ID (eg XYZ123456). This
designation was used in Eagle as attribute in our own Eagle
component libraries. Availability, price and suppliers were
exclusively managed in a similar SAP
(https://en.wikipedia.org/wiki/SAP_R/3) software. This is in my
opinion, the only real solution for a professional use of Eagle
libraries.
For my personal use I look to the web site of my favorite seller
and do it like Guillaume.

Freundliche Grüße / Kind regards

Friedrich
-----------------------------------------------
.... use NNTP:\\news.cadsoft.de and a
functional news reader like Thunderbird!
Re: Hard Lessons Learned (watch out for land mines) [message #163672 is a reply to message #163667] Wed, 14 October 2015 12:21 Go to previous messageGo to next message
Michael Kellett
Messages: 75
Registered: February 2012
Member
I'll chip in here although I don't use Eagle because the discussion of
libraries is close to my heart.

I totally agree with the point made or implied earlier that the
existence of a part definition in a CAD tool library is not  a good
reason to use it.

But I'll go much further - although market competition forces CAD tool
makers to build up these libraries they are mainly useless and encourage
very bad engineering practice.

The only standard library I use is the IPC footprint library and even
then I usually tune the footprints before use.

I don't use any other pre-made stuff because:
it may contain errors and checking is difficult
it doesn't reflect the process that will be used on my boards
the schematic symbols (for complex parts) are very unlikely to suit my
design intent
I have schematic symbols for standard parts  that I have used on
zillions of designs.
the library part will often use a numbering or naming scheme that
doesn't work for me so needs to be edited anyway.

So I cringe every time I see a request on E14 or elsewhere for  a
library for some part or other as if it was some special deal to make
one's own.

MK

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Re: Hard Lessons Learned (watch out for land mines) [message #163673 is a reply to message #163670] Wed, 14 October 2015 13:22 Go to previous messageGo to next message
shabaz
Messages: 190
Registered: October 2012
Senior Member
Exactly, I've seen the same thing with custom part codes.
The part stock, availability, suppliers etc is usually managed
separately. And separate part codes for assemblies and 'transformed'
parts, e.g. cable assemblies or (manually) matched components.
Another example, a satellite company will store batch information and
never mix with later purchased parts, even if they are from the same
manufacturer and supplier, to reduce risk.
So parts are "exclusive" to a particular build, spares and to any
subsequent re-orders of complete satellites.

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Re: Hard Lessons Learned (watch out for land mines) [message #163674 is a reply to message #163672] Wed, 14 October 2015 15:19 Go to previous messageGo to next message
shabaz
Messages: 190
Registered: October 2012
Senior Member
Hi Michael,

You've hit the nail on the head - it is competition forcing this and
it's getting silly.
Such supplied libraries really are at best only a slight 'convenience'
and often a hindrance.

Sadly many newcomers assumes CAD packages are awful because the
libraries are missing parts that they want - we can
refer to this thread from now on to show the valid reasons for building
their own.
Just to make it easier to search - byol byof (build your own library,
build your own footprints!)

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Re: Hard Lessons Learned (watch out for land mines) [message #163675 is a reply to message #163673] Wed, 14 October 2015 15:23 Go to previous messageGo to next message
Mark Archibald
Messages: 3
Registered: October 2015
Junior Member
First off, I am impressed with the skill and attention to detail
exhibited in your custom torroid library.  Nicely done!

Second, I appreciate the deep experience brought forward in this
dicussion.  The thoughts expressed here are actually valueable in a real
world context.

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Re: Hard Lessons Learned (watch out for land mines) [message #163682 is a reply to message #163675] Thu, 15 October 2015 04:05 Go to previous messageGo to next message
shabaz
Messages: 190
Registered: October 2012
Senior Member
Hi Mark,

That toroid library was a pain ; ) it takes into account wire thickness,
and ideal spacing to minimise capacitance between the turns.
And I had forgotten so much trigonometry..
I have a spreadsheet to calculate the number of turns based on desired
inductance basically, and use that as input to the tool to auto-generate
the part.

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Re: Hard Lessons Learned (watch out for land mines) [message #163769 is a reply to message #163615] Fri, 23 October 2015 15:09 Go to previous messageGo to next message
Don Hersey
Messages: 31
Registered: March 2014
Member
Out of curiosity, Shabaz, can you do bifilar and trifilar windings with
your scheme?  Can it handle xformers?

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Re: Hard Lessons Learned (watch out for land mines) [message #163776 is a reply to message #163769] Fri, 23 October 2015 17:16 Go to previous messageGo to next message
shabaz
Messages: 190
Registered: October 2012
Senior Member
Hi Don!

It can't, but that was next on the agenda. It should be easy to add that
capability in terms of landing pattern, but knowing
how to design it and how many twists is harder, most sources just state
an empirical number. Even dielectric constant
is guesswork when the wire manufacturers publish so little information :
( I've built some spreadsheets to do the calculations
based on formulas I've found over the years, but have yet to try to
measure any of it. I now have a VNA so can
learn a bit more. I think (not sure) in the past most of this was done
by careful experimentation for weeks/months until the transformers
were 'just right', and a shame that experience is being lost to some
extent perhaps.

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Re: Hard Lessons Learned (watch out for land mines) [message #163795 is a reply to message #163615] Fri, 23 October 2015 20:48 Go to previous messageGo to next message
Don Hersey
Messages: 31
Registered: March 2014
Member
'course the compute-intensive FEA method would not have been available
in the old days as well.

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Re: Hard Lessons Learned (watch out for land mines) [message #163796 is a reply to message #163615] Fri, 23 October 2015 20:47 Go to previous messageGo to next message
Don Hersey
Messages: 31
Registered: March 2014
Member
That has been my experience, sometimes they come out consistent with the
design eqs, often it is tweaking with metrology 'til the late hours.  I
imagine the old-fashioned alternative, stuff like Pi wound coils, would
have been an even bigger design nightmare, I cannot imagine modeling
capacitance on a multi-layer, funkily wound coil.  Sometimes, they would
make high-Q filters with them!  IIRC, we still don't even have
formalisms for something like a Y-shaped core.  Nor, IIRC, do we even
have a general formalism for capacitors.  We only have special cases,
like parallel plate, or conductive sphere near conductive plane, or two
spheres, cylinders.  Amazing that we are able to do so much when we are
so ignorant.

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Re: Hard Lessons Learned (watch out for land mines) [message #163798 is a reply to message #163795] Sat, 24 October 2015 08:39 Go to previous message
Rob Pearce
Messages: 487
Registered: September 2012
Senior Member
On 23/10/15 21:48, Don Hersey wrote:
> 'course the compute-intensive FEA method would not have been available
> in the old days as well.
>
No, but the principle was well-established. The reason we have the
simpler forms for some of the special cases is that some very clever
person looked at the FEA (he didn't call it that, but it's essentially
where he started) and did some complex maths to figure out the result.
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