Hard Lessons Learned (watch out for land mines)

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.

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?

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.

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.

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.

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.

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.