gEDA-user: Footprints and their symbols, conventions for

[Martin Maney <maney@xxxxxxxxx>]

A couple of questions that have come up as I've been making some
symbols and footprints for various parts for a project that I need to
send off real soon now:

Looking at Bill Wilson's guide to defining transistors (1), despite an
initial feeling of unease, I find I'm pretty much convinced this is a
good plan.  So how come I don't see evidence that it's ever been
implemented (or where did I not look to find it)?

A couple of parts I needed to draw both symbols and footprints for are
PC-mounting connectors for external connections - so they need to be
mounted at an edge of the board, with attention to aligning their
individual mounting planes with the intended location of the panel they
will mount to.  After pondering this for a while, I have come to the
not really savory conclusion that a small kluge is as good a solution
as possible: I placed the footprint's "mark" on the center line of the
connector's axis, in the plane of that external panel.  So in normal
use these would all be placed somewhat off the edge of the PC board,
which doesn't seem quite right, but does seem less awful than having no
indication of the mounting plane present at all (really didn't care for
having a silk line out there, although the vendor I expect to be using
says they simply delete such extraneous silkscreen marks).

There was one more... oh, right.  Not immediately relevant, but
pondering the location of the mark for the horizontal connectors led me
to think about the footprints for vertical mounting versions.  In this
case it seems to me that the mark should be placed at the center (for a
round bodied connector) or other mechanical reference point.  As with
the horizontal sort described earlier, the mounting requirements are
what really determines the placement, and PCB has to accomodate the
resulting pad positions, be they on the grid or off.

At least that's how my thinking is working today.  :-)


(1) http://geda.seul.org/wiki/geda:transistor_guide

-- 
During much of that epoch [the thirties and early forties],
I gained my livelihood writing for the silver screen,
an occupation which, like herding swine, makes the vocabulary pungent
but contributes little to one's prose style.  -- S J Perelman



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