Re: gEDA-user: Two Power Supplies in gschem

[Stefan Salewski <mail@xxxxxxxxxxxx>]

On Sat, 2011-04-02 at 19:02 -0300, Daniel B. wrote:
> Hi geda-user@,
> 
> I'm kinda new to gschem (in fact, first time learning a electronics
> cad software) and a little confused about the power pins issue. I read
> the geda-faq:gschem and found that it's a good practice to NOT hide
> the power pins.
> 
> Is this related to the design of the symbol? Are there some (generic)
> attribute common to all symbols that makes the power pin visible?
> 
> I'm trying to draw a circuit that uses 2 different power supplies, 12V
> and 5V. Are there any other good way to design this type of circuit?
> 
> Any old topic in archive might be helpful too.
> 
> Thank you in advance.
> 

A difficult point for beginners -- we should have an entry in the FAQ
for this. Short answer:

Symbols can have invisible power pin, i.e some logic gates symbols have
entries like

net=GND:7 or net=+5V:14 or net=VCC:14

If you put multiple such symbols on your schematic these pins (pin 7 or
14) are connected for the netlist, and later on the PCB board.

Today often multiple voltages are used, so hidden power pins can
generate problems, use of something like VCC can be bad, because it may
stand for 3.3V and 5V and may generates unwanted shorts.

So it may be better to always use explicit visible power pins -- use
power pin like other ordinary pins, connect pins with nets. You may use
Power-symbols like GND to give names to these nets, or you may use the
netname attribute to give names to nets. Nets with the same name become
connected. There is no magic to switch between visible and invisible
pins, the author of the symbols decides how he wants it. Things become
even more complicated when we put the visible power pins to a separate
symbol instance. You may find examples for all kinds of symbols at
  
http://www.gedasymbols.org/

DJs and Wilsons tutorial may help

http://www.delorie.com/pcb/docs/gs/gs.html
http://geda.seul.org/wiki/geda:gsch2pcb_tutorial

It is not easy for beginners, and my english is really bad today, sorry.
I hope someone other can explain it in better words.

Best regards,

Stefan Salewski




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