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Re: gEDA-user: pick and place ?plugin?footprints.c? for

Hi all,

FWIW, most mechanical CAD packages I'm familiar with (and even gschem)
use a insertion point and a rotation angle in the definition of grouped
drawing entities (a.k.a. symbol, drawing block, ..., whatever it is
named) somewhere within the drawing file (a.k.a. schematic).

So my EUR 0.02 proposal is to add this as an attribute value to the pcb
file within the element definition, maybe encapsulated within the
element body (according to the current file format), or as an extension
to the element header (change of the current file format).

Kind regards,

Bert Timmerman.

On Tue, 2008-02-26 at 10:24 -0600, John Griessen wrote:
> Dave N6NZ wrote:
> > 
> > Dan McMahill wrote:
> >> Dave N6NZ wrote:
> 
> >> Still, the suggestion about letting a footprint optionally include this 
> >> information to deal with "problem" parts might be an option.
> > 
> > Yes, even as I suggested it I considered it a band-aid.  If PnP info can 
> > be computed reliably, it should be done automatically. But let's face 
> > it, in every footprint library there are some footprints that are 
> > "higher maintenance" than others.  With a manually entered fall-back 
> 
> If a footprint contained another reference mark, (pick ooint), besides origin, it seems to
> me it would help.  Think of SMT connectors with offset solder islands for strength of
> grab to the board.  They're not symmetric, and hard to analyze so a mark that comes with
> them is the only way I can think of.  Since the mark has the single purpose of defining where
> is a flat spot your pick and place machine can grab, it wouldn't move around as people
> made footprint variants.
> 
> =========================
>  > Golden rule,  ask user on export.
>  >
>  > We could even show this data on a layer in PCB, or view this in gerbv
>  > as a ball at the centroid with a stick and arrow in the direction of
>  > the axis.
>  > This would allow a human to verify the axis and rotation.
>  >
>  > For pick and place if we are consistent than that is half of the battle.
>  >
>  > Hardkrash
> 
> [jg] I like this idea.  PCB seems the more likely place for the recognition code.
> The gerbv developers say a gerbv library call exporting to pcb format is "on the horizon", so
> a PCB plugin might call gerbv for the starting point gerber data to operate on.
> 
> I still see one area not discussed much, I don't think..), yet needing tricky recognition:  How do
> you identify which pads are in a footprint when starting from gerber data?  Especially
> if some libraries of footprints leave off silk, such as 0402s 0201s etc...?
> That step seems to require looking at pads plus trace exiting pad to decide
> which pairs of teeny pads go together for 2 terminal parts in rows.
> 
> Dave N6NZ wrote:
> ====================
>  > And then there are BGA's..... I'm not going to think about them tonight.
>  >
> 
> Those and land-grid-arrays need two fiducials near them says lilbro.  They aren't the big time-burners.
> Probably a pick mark is hard for non-symmetric land-grid parts, but the fiducials save you anyway.
> Probably OK to leave as "user supplied marks" and worry only about the rest of the part types.
> 
> 
> John Griessen
> back from Kinsale 7 March



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