Re: gEDA-user: Matching footprints with symbols

[John Doty <jpd@xxxxxxxxx>]

On Apr 14, 2010, at 12:27 PM, Amand Tihon wrote:

> 
> I think that having common guidelines would keep both projects independant but 
> ease symbols and footprints creation.
> 
> For instance:
> - Simple diode: anode is on pin 1.
> - Polarized capacitor: "+" is on pin 1.
> - Default TO-92 footprint is 1-2-3 when looking at the flat side, pins down
> - etc.
> 
> Do such guidelines exist ?

No, and they wouldn't work. The layout person is going to want numbers matching their own tool and footprint library. There are no standards here. The technician working on the board is going to want to see pin numbers matching the manufacturer's data sheet, and manufacturers have no common numbering scheme. gEDA can't unilaterally fix these problems.

> 
>> 3) There is consensus, that the current library is in poor shape. But
>> there are diverging opinions how a good default library should look like.
> 
> The net result seems to have been the creation of gedasymbols.org: a 
> collection of symbols, sometimes with matching footprints, that you still 
> cannot trust blindly because everyone has his own rules for pins numbering.

You can *NEVER* trust a library symbol blindly. In any EDA system. Period. Get over it.

> 
> John Doty said that the libraries shipped with gEDA should be used as starting 
> points. I tend to think that gedasymbols.org makes a much better starting 
> point.
> 
>> The default library of gschem is a known weakness. It was already in
>> exactly the same shape in 2005 when I started to work with geda.
> 
> Sadly, that matches my feelings about it.

Feelings don't matter. It's like complaining that there's no solution for the general quintic equation using radicals. It's a "known weakness" of algebra, but it's also known to be unfixable, so move on.

> 
>> I don't use the default lib and rely entirely on my homegrow symbols/
>> footprints.
> 
> Does anyone actually use the stock symbols ?

For a simple project there's nothing wrong with resistor-1.sym. For a more complex project, I generally want some project-specific default attributes like "footprint=0603" and "spec=1/16W,5%". The customer, layout contractor, and application have an influence here.

> 
>> All my symbols contain a default footprint. One of my favourite
>> feature requests is the ability to give a list of default footprints.
> 
> Is that a feature worth working on (I'm a developer, electronics is a hobby) ? 
> Or would such a patch be rejected without hope of being ever integrated ?

I think it's far more important to have the symbol browser import symbols into the *project* (not the schematic) as they are selected, so they can be customized as necessary. And it should pop up an annoying information box reminding the user to check the symbol until the user turns the box off.

John Doty              Noqsi Aerospace, Ltd.
http://www.noqsi.com/
jpd@xxxxxxxxx




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