Re: gEDA-user: DRC vs shorted nets?

[Stephen Meier <smeier@AlchemyResearch.com>]

Harry,

I did an simple example where I created an op amp, a power connector and 
shorted two planes together through one polygon.

Then I selected the ground plane and hit the f-key and as you can see 
both the +5 and the -5 pins of the op amp were  turned green along with 
the power connectors two pins.  pcb_nets_shorted.jpg

Then I selected one of the op amps power pins and again asked for the 
connected net.  Now both power pins, the ground plane and both connector 
pins turn green. pcb_short_ex2.jpg

For this simple example its not hard to find the error. So lets expand 
our example to a board with 10 opamps, 2 power planes and 1 ground 
plane. For each op amp we will typically use 1 inductor and 3 decoupling 
capacitors for each power pad. This equates to some 100 pads connected 
to various power pads. Each one needing to reach a via to take it to the 
appropriate power plane (20 vias). Plus there will be at least two 
resistors per op amp and a few capacitors scattered here and there for 
ac coupling. I can reasonably assume that there are at least 20 vias and 
maybe more. Now which via causes the short?  Still not to bad if all the 
devices use the same pinout but if you have a selection of pinouts. Then 
the issues keep getting more and more complex and figuring out where the 
mistake was gets harder and harder.

Don't get me wrong boards can be built with these tools. Its getting 
better faster and faster. I expect new features to be integrated in soon 
from unexpected sources....

A simpiler way to find goofs... either at the time of the error or back 
tracing (pun intended) to find the error would be usefull.

Thanks again,

Steve M.



harry eaton wrote:

> Steve,
>
> Perhaps you should highlight the plane you want connected to the net with
> the "find connections" (f-key), with rats in place, all pins/vias belonging
> to the net will get highlighted. Then it should be easy to see whether a
> thermal will be good or not - it should always be on a green pin/via over a
> green polygon. Turning off other visible layers to reduce confusion might
> also help.
>
> harry
> p.s. you can now also use the autorouter to make connections to ground/power
> planes, provided at least one such connection already exists in order to
> show it belongs to the net.
>
> ----- Original Message -----
> From: "Stephen Meier" <smeier@AlchemyResearch.com>
> To: <geda-user@seul.org>
> Sent: Tuesday, May 04, 2004 2:28 AM
> Subject: Re: gEDA-user: DRC vs shorted nets?
>
>
>  
> > I tend to create shorts most often using the thermal tool.  If I could
> > declair a layer to be reserved for one net then most of my mistakes
> > would be easy to spot.
> >    
>
>
>