Re: gEDA-user: gschem vs. PCB diode pin numbering - anode/cathode definition

[Vanessa Ezekowitz <vanessaezekowitz@xxxxxxxxx>]

On Thu, 25 Aug 2011 08:28:46 -0400
Ethan Swint <eswint.ramu@xxxxxxxxxxx> wrote:

> On 08/24/2011 01:15 PM, Colin D Bennett wrote:
> > On Wed, 24 Aug 2011 08:21:17 -0400
> > Ethan Swint<eswint.ramu@xxxxxxxxxxx>  wrote:
> >
> >> On 08/23/2011 08:47 PM, Matthew Lewis wrote:
> >>> I was double checking a pcb layout today and I discovered a rather
> >>> nasty gotcha. It seems that gschem and PCB don't agree on which end
> >>> of a diode should be pin 1. Gschem views pin 1 as the anode and PCB
> >>> considers pin 1 to be the cathode. It doesn't prevent you from
> >>> laying out a board correctly, but it does cause the silkscreen
> >>> polarity to be printed backwards (for the SOD devices at least).
> >> I've defined my own symbols and footprints to use 'A' and 'K' instead
> >> of 1 and 2.
> > That's a good idea.  Anything you can do to error-proof yourself is
> > a Good Thing.
> >
> > However, I refuse to use âanodeâ and âcathodeâ for diode symbols, since
> > these terms refer to electron flow and are _incorrect_ when the diode is
> > reverse-biased (most obvious for common Zener diode circuits).
> >
> 
> > I understand that it is electrical convention to name diode terminal
> > anode and cathode, but I reject it as a confusing and ambiguous naming
> > convention.
> Yes, it's not quite correct, but it is a widely held convention, unlike 
> numbering the pins 1 and 2 (or 3 or 4).
> > For my diode symbols and footprints, I choose to name the terminals
> > âPâ and âNâ (for the p-type doped side and the n-type doped side).
> If you use "P" and "N", Schottky diodes are now in error.  ;)

I am not an expert by any means, for in the 25 years I've dabbled in electronics, including a formal course in high school, it's always been "K" to designate the cathode (in addition to what the overall symbol implies, of course), regardless of the type of diode or the true direction of current flow.

New users, and those not on this list, are not going to be aware of this thread, and are going to expect the anode/cathode convention to hold - anything else unnecessarily complicates things, and could potentially lead to much bigger problems (i.e. an apparent unreliability of gEDA or PCB).

Why change what works for most electronics folks?

-- 
"There are some things in life worth obsessing over. ÂMost
things aren't, and when you learn that, life improves."
http://digitalaudioconcepts.com
Vanessa Ezekowitz <vanessaezekowitz@xxxxxxxxx>


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