kicad-developers team mailing list archive

[Heiko Rosemann <heiko.rosemann@xxxxxx>]

I strongly believe that's because many people come from Eagle originally
(even via a different professional tool) and Eagle has this distinction.
A symbol is what you place in the schematic, a footprint is what you
place on the PCB and a component is what defines their relationship (and
links to a datasheet etc.).

Example: A rectangle with three pins called VIN, GND and VOUT is a
symbol for a linear voltage regulator, could be called v-reg. The
footprint you choose for that symbol could be a TO220 with pads 1, 2, 3
and heatsink, an SOT23 with pads 1, 2, 3, an SO8 with pads 1..8...

The component "LM78Lxx" defines that for a variant LM78LxxACM, the
footprint is SO8 with Pad 1 used for Pin VOUT, Pads 2, 3, 6, 7 used for
Pin GND, Pad 8 used for Pin VIN and Pads 4 and 5 are Not Connect, for a
variant LM78LxxACZ, the footprint is TO92 with Pad 1 used for Pin VOUT,
Pad 2 used for Pin GND and Pad 3 used for Pin VIN.

In KiCad, we have a mixture of "symbols" to which you can assign "any"
footprint and "components" which have a footprint specified, and we call
both "symbols". Some of these symbols have pin numbers called "1, 2, 3"
to fit certain "neutral" footprints, some have pin numbers called "VI,
VO, GND" to fit a certain "special" footprint, some have multiple pins
for the same function... the 78(L)xx-series in the libraries I got for
stable-4.05 is a good example of this mixture, and it used to be much
worse a few years ago.

But then again, we have this discussion about once a year and it always
peters out after a while because nobody has the time to actually
implement a proof of concept (me included) so it can't properly be
evaluated, while the librarians do a great job improving the "standard
library" so people have it easier and easier to just use what's provided.

(What I'd definitely love to see: A more prominent warning if your
symbol has some pins that don't have matching pads in the footprint you
have assigned them. Preferably in cvpcb or whatever dialog will replace
it, not 10 clicks later when you're importing a netlist into pcbnew.)

Just my 2 cents,
Heiko

On 03/23/2017 03:14 PM, Jon Evans wrote:
> I agree with Simon.  I have plans to propose something like this in the
> future (i.e. an integrated part library that manages
> symbols/footprints/etc together) and it would be best to reserve the
> term "component" for this future use, since in my experience that's what
> "component" means in the big tools (I have not used Altium, but it is
> more of a "medium" tool than a "big" tool FWIW)
> 
> I don't have time to detail my proposal now, but basically I think a
> "component" should map to one or more footprints, one or more symbols,
> one or more vendor part numbers, one or more 3D models, etc.
> 
> -Jon
> 
> On Thu, Mar 23, 2017 at 8:33 AM, Simon Wells <swel024@xxxxxxxxx
> <mailto:swel024@xxxxxxxxx>> wrote:
> 
>     one of the things that irks me about component is even though its
>     meant to only be schematic being component libs a lot of the questions
>     asked in irc will state component when they use that as either a
>     generic term for symbols AND footprints or sometimes footprints only,
>     as to some i guess thats still part of a "component definition".
> 
>     If at some point down the line we did introduce some sort of package
>     that was symbol/footprint/model/spice/....... i think that would be a
>     much better thing to call a component.
> 

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