Re: gEDA-user: Embedded Power Pins

[sdb@xxxxxxxxxx (Stuart Brorson)]

> Stuart Brorson wrote:
> 
> > FWIW, I wrote a blurb about this question for the wiki a couple of
> > weeks ago.  Here it is: 
> > 
> > http://geda.seul.org/dokuwiki/doku.php?id=geda:faq-gschem#what_should_i_do_about_power_pins_on_my_symbolsmake_them_visible_explicit_or_invisible_implicit
> 
> Well, I agree only half way with you.
> It is true, that power pins in analog circuits should be visible on the
> schematic. But having them on attached to the triangular shape is not
> correct either. Imagine a quad opamp: If you use symbols with visible
> power pins, you get eight visible power pins.
> 
> My preferred solution would be a special slot just for the power
> connections. This is how we dealt with this issue in Protel99 and it has
> its advantages for circuits that contain lots of opamps. The power
> connections plus the necessary caps don't clutter the feedback loops. So
> the circuit is easier to read. Still the power pins are explicitly drawn
> and can be tied to some exotic net. I usually draw all the power symbols
> with their caps in some quite corner of the paper.
> The only drawback is that the supply caps are not in the neighborhood of
> the corresponding triangular  shape. But with quadamps the triangular
> shapes that belong to one component are scattered over the schematic anyway.
> 
> Nevertheless, I don't see how I could implement this technique with
> gschem. There seems to be no way to let a gschem symbol contain slots
> with different pinout. The same problem arises if a component has slots
> that perform different functions. This is the case for some analog
> multipliers that contain an additional opamp with no internal connection
> to the multiplier. Did I miss something obvious?

No, you are right.  Gschem's slotted parts must all use the same
symbols, I am pretty sure. 

For slotted opamps, I just wire up the power pins on slot 1, and
leave the power pins on slots 2 ... N unconnected.  Gschem & gnetlist
like this just fine.  (FWIW, Orcad *insists* that you wire the power
pins on *all* slots to *exactly* the same net.  It's a  real PITA.  I
like gschem better.)  

As for having a separate "power" slot on slotted parts: sounds like a
nice idea.  I don't know how much work it would take to implement in
gschem, but the work/payback ratio might be rather high . . . .

Stuart