Denny Esterline wrote:
> The next thing that caught my attention was all the varying width
> traces. Sure high power traces need to be larger, but some of your
> signal traces change width three times between components.
> I avoid running lines between IC legs when possible, if you ran the
> trace from 14-17 outside the chip, the connection to pin 15 wouldn't
> need to be run between the legs.
> The trace on pin 3 of the header could be run around pin one and avoid
> going between pins.
> The trace hooked to pin 20 has two unnecessary vias in it, it could be
> run entirely on top (even without moving it). As could the trace on pin
> 13. Symmetry is your friend, by moving d3-d6 around a bit, you could
> shorten the high power traces and clean it up a bit.
> I'd definitely look into using polygons for the high power sections.
> Did you intentionally not put a hole in the upper left corner?
> I tend to avoid traces at odd angles.

These are all good reasons to use the auto router except for critical areas.
However, the auto router doesn't absolve you from responsibility nor can you
expect it to just solve everything for you.  It's a powerful tool that can
be very useful in doing the parts humans are bad at, but you have to make
sure you stay ultimately in charge.

You've got a simple and small board, so learning the autorouter and then
using it to get a good result will take longer on this board than routing it
all manually.  After 2 or 3 small boards you'll be ahead and have a powerful
tool at your fingertips.  Sit down and completely read the autorouter
chapter in the manual.  Then make net classes for the various different
types of nets (signals, ground, maybe one or two flavors of power) in your
schematic and make sure that anything that isn't an ordinary signal is set
to a non-default net class.  Then go thru every one of the DRC settings so
you can see what the choices are and you are aware of what choices you are
making.  Then run AUTO and go thru every possible setting with the manual in
hand to remind you of what they mean.

For the first route, turn off all optimization passes.  The job of the
BUSSES and ROUTE passes is just to find a solution, so don't worry about how
messy it is.  Check all the trace widths and go back and fix the net classes
of the ones that showed up as thin signal traces when they were supposed to
handle power.  Now play around with some of the DRC and AUTO parameters to
understand their function better.

Once all the above looks correct, start turning on optimization passes.  I
usually use 8 optimization passes for final routes.

There is a lot more I could say about how to vary the parameters from ROUTE
accross the optimization passes, but that is really a full day course on its
own.

All in all I'm quite impressed by the Eagle auto router, but think of it as
a collection of fine jewler's tools instead of a sledge hammer.  It takes
time to learn and skill to use but once you're good at it you won't want to
be without it.


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