Mail Archives: geda-user/2013/10/13/11:18:20
On 13/10/13 15:26, Peter wrote:
> Some components (e.g. standard 4-pin tactile switches) have internal
> connections between pins, which is a feature I sometimes want to
> exploit to make routing easier.
>
> To deal with that, I've so far just given the internally connected
> pins the same name; when you connect just one of the pins, PCB will
> complain that the other one isn't connected, which can be worked
> around by connecting them with a trace on a "fake connection" layer.
>
> Now, however, I want to do the same with a surface mount component.
> The "fake connection" trick doesn't work there, because all
> connections need to be on the same side as the pads, so I'm wondering
> if there's a better way to do it that doesn't involve heavy editing of
> the schematic, and that will still stop PCB from telling me I need to
> connect the pads.
>
> So basically, suppose I have, for example, a surface-mounted tactile
> switch as follows:
>
> 1a |__| 2a
> |##|
> |##|
> 1b |¯¯| 2b
>
> Pads 1a and 1b are internally connected and are both called "1" in the
> footprint. In the schematic, I just have a 2-pin switch. I'd like for
> PCB to recognise a connection to either pad 1a or 1b as a connection
> to *both* pads, without having to edit my schematic to make all of the
> switches have 4 pins. (That problem with that would be that I'd have
> to edit the schematic a lot during the PCB design process, which I
> want to avoid.) Is there any current way to do this in PCB? If not,
> should I just ignore the remaining rat lines?
>
> Thanks in advance,
>
> Peter
>
Hi Peter,
Perhaps you could instead use a symbol with four pins like you have
'drawn' above... then you could also use the footprints with pads
numbered 1-4. You could show the connection in the symbol easily, with
the design intent clearly set out in the schematic.
When it comes to PCB, it would still complain about the pads not being
joined, but ignoring the rats between switch pads doesn't seem too awful.
When I complete a PCB layout, it's quite common for me to short ground
planes to connector shells... these don't always have the corresponding
pin in the schematic. Usually by the second revision of the design I've
tidied these up and added the appropriately numbered pins to symbols to
show these connections and prevent PCB from complaining. ;-)
Hope that helps...
Ed
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