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Re: gEDA-user: new footprint guidelines
Rick Collins wrote:
At 05:34 PM 10/1/2010, you wrote:
Rick Collins wrote:
>>If for whatever reason the designer used 2 different footprints for
>>the same part occuring
>>several times on a board, if the footprints are position/rotation
>>inconsisten...
>
> I have no idea why anyone would do that.
Real world example:
PhD student Foo designs some super noiseless detector circuit. The
measurements turn out a success. Researcher Bar, a long time friend who
works on some unrelated project, asks Foo for help to get him started on
noiseless detector. PhD Foo gladly provides the schematic and layout.
For
his project Bar needs to add some minor features to the hardware. Of
course,
she uses a different local library than Foo ...
> Sure the designer can totally screw up a design.
I wouldn't call this totally screwed.
If you work on a design and use a different, incompatible library from
the original without checking for consistency, yes, the designer
totally screwed up.
Again, yes and no: in our present state of standardization probably. But
at least
the designer didn't screw up alone: the guy who did much more is the
library builder.
That one is the person, responsible for conformance to standards in the
first place.
And that's our subject in the thread: "new footprint guidelines" - what
is considered
trusted fact in construction involving cooperation must be based on
standards
- and they evolve. There was a time, metric screws or Whitworth screws etc.
didn't exist. Every supplier defined screw gages as he pleased and a
designer,
who didn't check, that the nuts fitted on the bolts, screwed it up.
I really have no idea how things work in the gEDA/PCB world. With
FreePCB the library has a default orientation for parts and there is a
centroid vector to allow the pin 1 orientation to be set compatibly
with the Gerber files. If you use someone else's design you need to
verify that their library parts were done correctly or you need to use
the same footprints which are a part of the layout and so are
available. There is no reason to screw up something as simple as this.
How the Gerber file looks depends on the footprint definition. Once one
knows *exactly*
a) how the transformations work
b) that all libraries/generators(/custom made footprints) conform to a
sensible standard
checking is as superfluous as with screw diameters and pitches and
before that point
I don't believe it's simple enough.
Oh, I almost forgot, NEVER ask a PhD "anything" to design PCBs. What
the heck are you thinking???
As I may go the route to PhD if I find the time and a worthwhile subject,
I'm glad we are talking about this now, before I have started ;-)
Btw. to achieve standard conformance, the gschem symbols of polar
devices have to be
checked/reworked as well. The best solution probably is, to explicitly
attribute
conformat libs and keep them under their own section on gedasymbols.org.
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