kicad-developers team mailing list archive

[Vesa Solonen <vesa.solonen@xxxxxxxx>]

05/04/14 01:23, Heiko Rosemann kirjoitti:
> On 04/04/2014 10:45 PM, Carl Poirier wrote:
>> I think this is a very good idea. I will add this to our upcoming
>> KiCad library convention. Many transistors use letters already.
> 
> I do not agree for footprints, because - at least if I understand 
> the proposal correctly - it will lead to many many different 
> footprints of the same housing, i.e. an SOT23-EBC, an SOT23-SGD 
> (for FETs), an SOT23-CBE, an SOT23-A1-C-A2, an SOT23-A1-C1A2-C2 
> etc. pp. with all the same dimensional data but different pad 
> names.

This is the current state, because of the limited data model. I agree
with you that it's not how it should be. Regarding diodes one can get
_any_ orientation single ones in SOT-23

> I came to kicad from Eagle some years ago and I still believe 
> distinguishing between symbol-package-device to be the best 
> solution for this problem.

Second that. The implementation inside Kicad is not there yet. The
symbol is somewhat hard linked to the footprint (because symbol have
to contain matching pin numbers) and even the alias system can not
solve the issue.

Diode pad names ought to be generated when the component is
instantiated from the symbol, footprint _and_ "device description
data". The device description data is currently embedded in the symbol
and alias system, but that is clearly not working well enough.


An example:

SYM: Diode:–>|–, pins:2, name:A, name:C

FP: DO-214AB, pads:2, number:1, number:2, (numbers from JEDEC standard)

Device 1
DDD: Device: 5.0SMDJ11-UNI
     symbol: Diode
     footprint: DO-214AB
     pin-pad-mapping: (K,1),(A,2) [no permutations]
     manufacturer: Protek Devices
     function: Transient voltage suppression 11V
     keywords: TVS, zener, diode
     data_sheet:
http://www.protekdevices.com/Assets/Documents/Datasheets/5_0smdj.pdf

Device 2
DDD: Device: SS3H10
     symbol: Diode
     footprint: DO-214AB
     pin-pad-mapping: (K,1),(A,2) [no permutations]
     manufacturer: Vishay
     function: Surface Mount Schottky Rectifier 100V
     keywords: schottky, rectifier, diode
     data_sheet: http://www.vishay.com/docs/88752/ss3h9.pdf


Pin-pad-mapping is expected to contain all gate and pin swap
permutations for devices that allow it, simple devices like
bidirectional TVS zeners and resistors would just have x as a pin name
for interchangeable ones.

>> As for capacitors, why not also using C and A for cathode and 
>> anode?
> 
> In my experience, the terminals of a capacitor are not called 
> cathode and anode.

Only polarised (electrolytic) ones will have cathode and anode, but
elsewhere that would be misleading. Rolled foil capacitors used to
have some marking which lead was connected to the outermost electrode,
so one could make the orientation such that the outer electrode
protected the other form interference (like capacitance changes from
nearby objects). Precision polystyrene capacitors especially. Lately
I've seen such in modern PTFE ones.

-Vesa