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Thread

eagle autorouting - got any tips?

2005-06-05 by David McNab

Hi all,

I'm having some weird times with CadSoft Eagle's autorouter.

The project is based on a 28-pin PIC device, on a single sided board,
with a moderate number of peripheral devices and passive components.

Eagle's autorouter is an absolute god-send, but is incomplete in the
sense that it can't automatically change component placement (within
user criteria) to achieve greater success.

I'm trying to autoroute the bottom side of the board to minimise the
number of unrouted connections. This is challenging, because due to
physical requirements, several components have to stay in fixed
positions on the board. At best, I'm getting down to 4 or 5 unrouted
connections, which I could solve with manual vias and top-side wires,
but I'd really like to get it down to 0 unrouted.

I tried 2-side autorouting, and setting high costs for vias, as well as
maximum numbers of vias. But the autorouter seems to ignore these, and I
end up with 30 vias or more.

My experiences with the autorouter have been weird to say the least. It
feels like I could get more scientific certainty from inspecting chicken
entrails to predict movements in the NASDAQ.

If anyone here has got Eagle autorouting down to a fine art, would you
care to share your tips to help myself and others learn from your
experience?

Thanks in advance
David

Re: [Homebrew_PCBs] eagle autorouting - got any tips?

2005-06-05 by Leon Heller

----- Original Message -----
From: "David McNab" <david@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Sunday, June 05, 2005 4:57 AM
Subject: [Homebrew_PCBs] eagle autorouting - got any tips?

> Hi all,
>
> I'm having some weird times with CadSoft Eagle's autorouter.
>
> The project is based on a 28-pin PIC device, on a single sided board,
> with a moderate number of peripheral devices and passive components.
>
> Eagle's autorouter is an absolute god-send, but is incomplete in the
> sense that it can't automatically change component placement (within
> user criteria) to achieve greater success.
>
> I'm trying to autoroute the bottom side of the board to minimise the
> number of unrouted connections. This is challenging, because due to
> physical requirements, several components have to stay in fixed
> positions on the board. At best, I'm getting down to 4 or 5 unrouted
> connections, which I could solve with manual vias and top-side wires,
> but I'd really like to get it down to 0 unrouted.
>
> I tried 2-side autorouting, and setting high costs for vias, as well as
> maximum numbers of vias. But the autorouter seems to ignore these, and I
> end up with 30 vias or more.
>
> My experiences with the autorouter have been weird to say the least. It
> feels like I could get more scientific certainty from inspecting chicken
> entrails to predict movements in the NASDAQ.
>
> If anyone here has got Eagle autorouting down to a fine art, would you
> care to share your tips to help myself and others learn from your
> experience?

Most autorouters are a waste of time, especially on single-sided boards. The
Eagle autorouter is crap, anyway.

If you want a decent autorouter have a look at Electra, it's available for
Eagle. I use Pulsonix for PCB layout and it comes with Electra as an option.

Leon
--
Leon Heller, G1HSM
http://www.geocities.com/leon_heller

Re: [Homebrew_PCBs] eagle autorouting - got any tips?

2005-06-05 by Alan King

Leon Heller wrote:

> ----- Original Message -----
> From: "David McNab" <david@...>
> To: <Homebrew_PCBs@yahoogroups.com>
>>
>>I'm trying to autoroute the bottom side of the board to minimise the
>>number of unrouted connections. This is challenging, because due to
>>physical requirements, several components have to stay in fixed
>>positions on the board. At best, I'm getting down to 4 or 5 unrouted
>>connections, which I could solve with manual vias and top-side wires,
>>but I'd really like to get it down to 0 unrouted.

Hard to tell 100% from your wording, but if you mean a single sided board and
get it to 0 unrouted, realize that this is quite likely impossible. Very few
topologies with more than one IC or connector that has fixed pin locations will
result in a board that can successfully be fully routed on one side with any
amount of effort.

>>
>>I tried 2-side autorouting, and setting high costs for vias, as well as
>>maximum numbers of vias. But the autorouter seems to ignore these, and I
>>end up with 30 vias or more.

The cost for vias is relative to the cost for other steps etc. Vias not only
have to go up, other costs have to go down. You also have to have it work the
right way through the several passes of the autoroute, so that it is constrained
to head your board towards the correct final result.

>>My experiences with the autorouter have been weird to say the least. It
>>feels like I could get more scientific certainty from inspecting chicken
>>entrails to predict movements in the NASDAQ.

> Most autorouters are a waste of time, especially on single-sided boards. The
> Eagle autorouter is crap, anyway.
>

Eagle autorouter is one of the more brilliant things I've ever used. The
defaults are simply poorly set up for how most people want it to work, they need
to make a couple of easy load classes for single sided etc. What I've made it
do on more than a few times is far better than the settings it shipped with. It
takes quite a bit of playing around to start to understand it, but once
understood you can make it work any way you like and it's very good at it. Very
high costs for top with adjusted lowered costs for bottom, and only letting it
even try top on the last pass or two can easily get it to route a minimum number
and length for top side jumpers.

You also seriously have to play around adjusting single settings to extremes
so you know what they do. Bonus step is an extra step in the same direction
going toward the goal. Malus step is an extra step in the continuing direction
but going further from the goal. Sometimes it gives lower cost to take a few
bad steps and then get around something etc. You have to really learn what
everything is doing, and learn to adjust it vs the other settings, and learn to
do that vs the multidimensional effect of many passes. Takes quite a bit of
playing but it's not at all impossible.

I couldn't even tell you the exact settings right now though, the last board
or two I did were very straight forward single sided with special locations so I
did them manually. Haven't set the autorouter up fully since the last time I
upgraded, I end up adjusting it to match what I need for complex boards anyway
so don't usually bother taking the settings along with the upgrade. I just
figure them back out when I need them.

On the other hand, 15 minutes of playing around with one of my old boards
would get it where I could give you some more specific ideas of how to use it.
Have too many other things going on right now, but maybe I can mess with it
sometime shortly. It also pops up in the SRS group now and then, everyone says
it sucks then I say it's the best thing since sliced bread. Something to write
up a how to guide for at some point, it's just a very back burner thing.

Alan

Re: [Homebrew_PCBs] eagle autorouting - got any tips?

2005-06-06 by Earl T. Hackett, Jr.

I gave the Eagle auto router a try - and promptly gave up. I routed the project by hand and got a reasonable layout. If an autorouter is given a pile of layers and internal vias to work with, it will probably come up with something useful, if not optimum. Constrain it to 1 or 2 layers and it will throw a fit. Reality is that it doesn't pay a commercial enterprise to spend time figuring out how to get rid of a few circuit board layers - 6, 8, or 10 layers, who cares. If the design works, just build it and pass the cost on to the consumer. All the competitors are working under the same constraints, and time is your biggest enemy.

However, I need 50 or 100 boards and I don't want to spend more than necessary (meaning my money) to get the job done. This is a very different viewpoint as compared to the typical high tech company.

I must say that I found the Eagle software extremely efficient. Once you get used to it, the Eagle interface is very easy to use - about the best I've ever seen. Maybe Microsoft should pay attention.

[Non-text portions of this message have been removed]

Re: eagle autorouting - got any tips?

2005-06-07 by workaholic_ro

Just to say that I totally agree with this. I've been using Eagle many
times in the last two years, It's fiendly, fast and eficient. Of
course their are much more sophisticated software packages claiming
that the human brain is useles since they do everything and we can
have our beer watching TV while they do all the job. You only have to
be patient for three or four years to learn Orcad and you'll never
have to do anything for the rest of your life but to tell the machine
what is to be done (and enjoy the beer of course).

Luck to all

worka.

P.S. Ad LTSPice to help for schematics (its free at Linear
Technologies) and you'll never regret - much better than many
commercial software.
Nota bene: I have no connection with theese companies, I'm just a
simple user and I rather drink wine and work than beer and watch.

>
> I must say that I found the Eagle software extremely efficient.

Once you get used to it, the Eagle interface is very easy to use -
about the best I've ever seen. Maybe Microsoft should pay attention.

>
> [Non-text portions of this message have been removed]

Re: [Homebrew_PCBs] Re: eagle autorouting - got any tips?

2005-06-07 by Stefan Trethan

On Tue, 07 Jun 2005 16:24:49 +0200, workaholic_ro
<workaholic@...> wrote:

> Just to say that I totally agree with this. I've been using Eagle many
> times in the last two years, It's fiendly, fast and eficient. Of
> course their are much more sophisticated software packages claiming
> that the human brain is useles since they do everything and we can
> have our beer watching TV while they do all the job. You only have to
> be patient for three or four years to learn Orcad and you'll never
> have to do anything for the rest of your life but to tell the machine
> what is to be done (and enjoy the beer of course).
> Luck to all
> worka.

Have used orcad for three or four years. I must have done something wrong!!

I am never satisfied with autorouter results, and no matter how i set it
up the orcad router was no better.

I insist PCB layout is a form of art, and a machine can not create art.

ST