good advice in general.  I've long ago given up on the
autorouter.   In general, I've found that manual
routing isn't that hard and gives you a much better
feel for the board you are making.  After you've done
a couple, you'll get a good sense of how to place
things so they route easily.

If you want a truely single sided board, you may have
to really work at it.  I get good results by making
one side a ground layer and that tends to really
simplify the problem.  It also makes for a quieter
board.

To get good logical component grouping from the start,
I lay out the schematic in such a way that the
components of each subcircuit are near each other.  I
name and lable nets and dont necessarily run actual
nets between connected pins.  This allows the
schematic to be layed out somewhat akin to the board
layout.  Then parts are somewhat logically group on
the board when I create it from the schmatic.  

Pin and gate swap is useful though you may have to
tweak the libraries (74xx libs seem to be deficient
there) - its a good idea to examine the libs 'cause
they aren't always right.  Its pretty suprising how
many libs have all the pins at swap level 0.  You
might also consider changing pin assignments on your
PIC based on simplifying routing.  switch back to
schematic and change them.  Many pins are
interchangable (though not all, take care).

I actually route all the short runs first and then do
power/gnd.  With a ground layer, the power is usually
easy to route.

Phil

shouldn't this be tagged EE rather than OT?

 
--- Robert Young <rwyoung@ieee.org> wrote:
> ----- Original Message ----- 
> From: "jrem" <jrem123@yahoo.com>
> To: <piclist@mit.edu>
> Sent: Sunday, May 29, 2005 11:08 AM
> Subject: [OT] Eagle board layout questions
> 
> 
> > I am looking for Eagle Light clues for the best
> way to layout a single
> > sided board with the minimum number of top side
> routings and vias.  Are
> > there any hints as to board layout which can help
> me accomplish this?
> > I typically lay out the board then move stuff
> around, ripup, ratsnest,
> > and auto to try to minimize the top laer routings,
> but I never can seem
> > to get it optimized.
> >
> > Thanks, John.
> Some very GENERAL suggestions.  Your milage may
> vary.
> 
> 1) Don't bother with the auto router for a single
> layer board.  Do you
> yourself.  It is an OK autorouter but sometimes it
> just isn't worth fooling
> with.  This sounds like one of those times.
> 
> 2) Watch the rats nest when initially placing parts.
>  Keep in mind that you
> can switch back to the schematic and swap gates and
> if necessary re-connect
> pins (ie exchange A for B on 2 input AND gate).
> 
> 3) When routing, route power and ground first as
> these are going to be
> serpentine traces on single sided boards.  Use wider
> than normal trace
> widths for power and ground.
> 
> Item #2 is probably going to pay the biggest
> dividends.
> 
> Rob
> -- 
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