[Coco] WAS new mylars, NOW PCB Design

Tue Aug 11 16:14:06 EDT 2015

I'll start at the end:
"It’s a lot of fun building things,
isn’t it?  :)"

Oh yeah!!!

Thank you starting this thread.

I think my gravest error with my first board is that I did not use any decoupling caps. I knew these are important, but decided to not include them because my board gets it power from the PC's USB port. I should not have assumed that the 5v was clean.just because it had been "preprocessed" by the PC.

Way back then when I managed product design I got a chance to work with the PCB layout engineer and understand the the trails of getting everything routed. I captured the schematic using ORCAD and the engineer imported the nets into PADS PCB. The engineer then took up to 4 weeks routing everything. He initially would autoroute, but then would manually work with each one individually. Since there were 4 layer boards, two of these were reserved for power and ground and the other two for traces. This was akin to solving a complex puzzle, sometimes leading to a dead end. In that case the engineer would start from scratch to find another way to route. Usually the first 90% of the traces were no problem. It was the last 10% that provided a challenge and the last 2% that determined whether the board could be routed or not. At times the engineer changed the placement, taking into account any placement that was critical.

I learned enough from this engineer to know that various factors have to be taken into account, some of which you mention.

Fortunately, I did include a pseudo ground plane (meaning that I have a ground plane, but it only covers part of the PCB) so at least I can say I am headed in the right direction (even if I am not there yet. The ground plane covers all ground connections except one. I have traces on that layer too. As I learn more I hope to make the boards more efficient and robust.

Great tip on building your own component library. I had to do that to include an Arduino Nano in the design. It came out better than I expected, but still with a few holes (For one, I missed adding the silkscreen to define the component outline)..

Thanks for offering to share. I am ready to learn as much as I can.

Salvador

-----Original Message-----
From: Zippster <zippster278 at gmail.com>
To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
Sent: Tue, Aug 11, 2015 12:26 pm
Subject: [Coco] WAS  new mylars, NOW PCB Design

Hi Salvador (and all),

I certainly understand just wanting to use the
autorouter when you’re starting out,
there’s just so much to learn, it’s too
much to tackle everything at once.  A few things I’ve 
learned (and I’m still
learning every day, there’s an endless amount to learn in electronics
design).

Once you get familiar with your CAD software, I think a good way of
starting in on manual
routing is to concentrate on the power distribution at
first.  

Run power supplies to all ICs and circuits first, don’t worry about
ground lines during this first step, 
use a ground plane and ground should be
available almost everywhere on your board.  I wouldn't worry
about a power plane
on 2-layer boards, there won’t be any room for one, and the ground plane is
more
important.

Then decouple all IC’s properly.  One lead from the decoupling cap
as close to the positive power 
supply pin on the IC as is reasonable, the other
lead into ground plane on the bottom of the board
(where the ground pin on the
IC will also go).

Try to keep all traces on the top layer, going to the bottom
copper layer only when necessary, to 
preserve your ground plane.  When running
traces on the bottom layer be sure to leave pathways through
the ground plane as
open as possible, to avoid breaking it up.  Try to keep in mind where the
ground
connection to your board is and leave direct paths (straight-line more or
less) to it when you have a choice.

The part about keeping traces on the top
layer as much as possible becomes even more important when you
move to SMT
devices later, where you can’t naturally switch layers at any connection.  Your
via count goes 
through the roof if you don’t learn to keep most of your traces
on the top layer.  Part placement is critical to this.

One good way to start
working on efficient part placement is to begin while drawing your schematic. 
Lay out
your schematic with the final board in mind, keeping connections as
direct as possible with minimal crossings
(this is layer switching when you get
to board layout).

One other important CAD tip.  Get proficient in drawing up
parts from data sheet specs early, and don’t hesitate
to draw up a part rather
than search for one that’s already done.  You’ll get a better part for your
purposes,
and begin to build up a library of parts that you’ll use many times in
your designs.  You can optimize them for
assembly of the final boards as
well.

This is all just my opinion of course, everyone has their own way of
working.

I think it’s great that we use the resource of this group to learn
from each other and make our hobby even better.
I’m happy to discuss this stuff
anytime on the list or in off-list email.

It’s a lot of fun building things,
isn’t it?  :)

- Ed

> On Aug 11, 2015, at 11:14 AM, Salvador Garcia
<ssalvadorgarcia at netscape.net> wrote:
> 
> 
> 
> Anyway, nearly irrelevant
side-track over… 
> :)
> 
> - Ed
> 
> 
> Actually this deserves its own thread.
I think it is important to discuss these topics as this might spur interest in
developing more hardware for the CoCo and other vintage systems. I am getting
started on PCB design. At this time I am in the "I don't care" stage and let the
autorouter do the work for me. I tweaked the ground trace to create a plane, but
definitely know the value of doing the routing by hand. 
> 
> 
> I would have
been happy to offer Kip my help with his 3 or 4 projects, taking the schematic
and managing the PCB design and logistics, but I do not have the skill as of
yet. A transfer of knowledge within our community means that we could further
organize ourselves to motivate and support further innovations based on vintage
technology.
> 
> 
> Salvador
> 
> 

> 
> From: Zippster
<zippster278 at gmail.com>
> Subject: Re: [Coco] new mylars
> Date: August 11, 2015
at 10:44:27 AM CDT
> To: CoCoList for Color Computer Enthusiasts
<coco at maltedmedia.com>
> 
> A side note to laying out circuits with Eagle or
similar and using the autorouter.
> If there was one piece of advice I’d give on
autorouters, it would be to pretend they
> don’t exist.
> 
> It does take a long
time to lay things out manually, but it’s well worth it.
> Even a well-designed
circuit with good component placement on the board gets
> very meh when the
autorouter is applied to it.
> 
> Are autorouted boards functional?  Yes,
usually.  They are also terribly inefficient in terms of
> vias and proper power
distribution (proper ground plane especially).  Also, they destroy layout
>
aesthetics, which might not matter to some, but I think is important.
> 
>
Anyway, nearly irrelevant side-track over…  :)
> 
> - Ed
> 

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