Re: gEDA-user: Symbols and footprints and stuff, oh my

[Dan McMahill <dan@xxxxxxxxxxxx>]

Martin Maney wrote:

So I've been fairly happy with these tools (currently using the
> packaged stuff from Ubuntu's Gutsy release), but there are a couple
> little things I've run into, aside from the peculiar behavior that
> arises when one tries to make an oval pin and use it in a ground
> plane...
> 
> So I did a smallish circuit full of discrete transistors and Rs and Cs,
> and found usable footprints for all of them, but the pins from the
> transistor symbols - npn-2 and pnp-2 - didn't match the numeric pin
> names on the footprints. 

This is a known problem in the current flow.  I think the right answer 
here is to use a script to generate a library of heavy symbols for 
things like transistors.  Search for a post by me that has something 
like symbol generator in the body.

> gsch2pcb spit out a script that I would have
> thought was intended to deal with that sort of thing, but no, it's all
> just identities like this:
> 
> ChangePinName(Q9, E, E)
> ChangePinName(Q9, C, C)
> ChangePinName(Q9, B, B)

On some other symbols, you might see things like the pin called "1" 
being renamed to "IN" or "OUT".  That file is purely for cosmetic 
purposes, i.e. if you skip it, your final artwork will not change.

> I thought I did everything as described in the schematic-to-pcb
> writeup, but if this makes you think I forgot a step don't hesitate to
> mention it, of course.
> 
> Then there's the footprints, which are good enough to use but not
> ideal (eg, the m4 TO92 calls out pin 1 backwards from what seems to be
> the usual practice for that package, at least for the inline-pins
> variant; then too, I don't really want that square pad, useful as it
> was for identifying the numbering the footprint used).  While chasing

Does it match the JEDEC drawing?

> links all over creation, I came across Bill Wilson's discussion of
> transistor pinouts:
> 
> http://furrr.two14.net/cgi-bin/dwww/usr/share/doc/geda-doc/wiki/geda_transistor_guide.html
> 
> At first I didn't care for it, having used other tools with a more
> heavyweight symbol approach, but I've decided he's on to something. 
> I'll talk about a half-formed thought about a possibly better
> compromise between lightweight and heavyweight symbols, but for the
> moment I'm just wondering if (1) Bill's approach is generally approved
> of, and (2) if anyone's already run up footprints (I guess the existing
> symbols will suffice, aside from that letters vs numbers thing) for
> this approach.

I personally thing a heavyweight symbol library is the only way to go.

I hacked together a proof of concept thing for transistors and it works 
well.  I posted it to the list a while back.  I'd send again, but I'm in 
the middle of trying to find a computer to read that hard drive :(

-Dan



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