Re: gEDA-user: Matching footprints with symbols

[John Doty <jpd@xxxxxxxxx>]

On Apr 14, 2010, at 10:41 AM, Amand Tihon wrote:

> Hi everyone.
> 
> I'm new to this list, and a very occasional gschem/pcb user. I make probably 
> one or two small boards per year, single layer. Most of the time using 
> through-hole components because that's what available at my local shop.
> 
> My question may sound silly or may even have been asked countless times: 

Yep. And the problem is that we downplay the truth: the library symbols are only starting points, not sensibly used as-is.

> 
> Are there any official guidelines for naming/numbering pins and pads on 
> symbols and footprints ? Some packages have an obvious numbering like DIP, but 
> what about capacitors, diodes, transistors, etc. ?
> 
> It could be due to my distribution (Debian), but I always get lost in the 
> symbols and footprints libraries that come with gEDA. Finding the right 
> footprint with correct pin numbering has always been a challenge. 

Yep. The problem afflicts all EDA systems because there are no universal standards for the physical parts. One even encounters DIP packages with reversed numbers occasionally (Minicircuits).

> 
> For instance, there are 3 different LED symbols. One in "Basic devices", two 
> in "Diodes (generic)". Two of them have the anode on pin 1, the third one has 
> it on pin 2.
> When trying to find a footprint for it, there are more than five for each of 
> 3mm and 5mm LEDs. For *none* of them does the silkscreen indicate the position 
> of the anode or cathode. LED3 and LED5 from pcblib/~geda actually present this 
> information in their name/description: "(pin 1 is +, 2 is-)". 
> In pcblib/~optical, however, the squared pin is named "-" (in red in preview, 
> still not on the silkscreen).
> 
> How do you usually handle this ?

Copy the symbol file into the project's symbol directory and edit it to match my project's parts and design flow. Might be nice for beginners if the GUI did the copy, although it's trivial from command line.

> Maybe you are able to remember what footprint 
> will match which symbol, but I don't use gEDA often enough for that.
> Or do you build your libraries of symbols and footprints that you *know* (or 
> hope) are correct ?
> Perhaps the state of the SMDs footprints is not that bad ?
> 
> I'm now slowly building my own libraries of footprints and heavy-wheight 
> symbols, to avoid mismatch between symbols and footprints.
> 
> Another reason I'm doing it is because I drill the holes by hand whithout any 
> drill-stand: my footprints have large (60 or 80 mil) pins that allow for some 
> imprecision, with 15 mil drill hole to have the drill bit position itself 
> right on spot, thanks to the copper thickness :)
> The drawback is that those footprints are obviously unusable if I ever need to 
> have a board manufactured.
> 
> Thanks for your answers.
> 
> -- 
> Amand Tihon
> 13C Rue Arsène Matton, 1325 Dion-Valmont, Belgium
> +32 479 207 743
> 
> 
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John Doty              Noqsi Aerospace, Ltd.
http://www.noqsi.com/
jpd@xxxxxxxxx




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