[sdiy] Free CAD (was: Proteus software)

[Ingo Debus]

Am 21.02.2011 um 21:04 schrieb Tom Wiltshire:

> In any half-way decent software, you ought to be able to change the  
> package or footprint for a device without having to completely  
> redraw the schematic

In Eagle this is easy, even if the pinouts are different as long as  
the pin count is same. It may become tricky, if not impossible, if  
the one device has more pins than the other (like replacing a 40 pin  
DIL IC with a 44 pin PLCC version).

But I think Jay's scenario was a different one:
1. draw a schematic intended to be used for two different layout  
versions.
2. start doing the layout version one.
3. start doing the layout version two (in Eagle now you would  
probably make a copy of the schematic with a different name or in a  
different folder. Then, in the copied version, you would "replace" or  
"change package" of the components that require a different footprint).
4. Oops! Now you have to change something in the schematic again.  
After doing this, you have to do all the "replace"/"change package"  
work of step 3 again. This can get annoying if it happens several  
times...

I think this is a general problem if several versions of anything are  
to be maintained. It happens in software development quite often.


But where Eagle really stinks IMHO is, if you have completed the  
layout and want to tidy up the schematics afterwards. It would be so  
easy to delete some connections in the schematics and re-route them.  
Don't do that!! Eagle always tries to keep schematics and layout  
consistent, so if you delete something from the (correct but untidy)  
schematic, it automatically deletes "something" from the (perfect)  
layout. Now it's your job to find out which (ever so tiny) trace was  
deleted and re-route it.
It is almost always possible to tidy up a schematic without deleting  
anything, just moving and shuffling things around. But it's puzzling  
sometimes.

Ingo (Eagle user for almost six years by now)