Homebrew PCBs

----- Original Message ----- 
From: "Phil" <phil1960us@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Wednesday, August 04, 2004 5:57 PM
Subject: [Homebrew_PCBs] Re: advanced routing


> Lots of good ideas, Leon.  I use most of them as well.  Wish eagle
> allowed the colored "air wire" thing as i spend too much time
> checking to see it is a supply connection.
>
> My wife did PCB design for many years and I asked her the advanced
> routing question.  She just laughed, shook her head and
> said "beginners. there is no magic book".  No suprise to me.  It just
> boils down to a set of design rules and techniques.  There is no
> substitution for experience.
>
> A couple more thoughts:
>
> I spend a lot of time looking at the schematic trying to get a sense
> of what goes best with what.  This helps me to place components in
> their best position.  I have a dual monitor set up so I can keep the
> board on one screen and the schematic on the other.  That really
> speeds up placement.

I do that as well. Pulsonix has a 'Group' facility that allows components to
be grouped on the schmatic so that they are associated on the PCB but I keep
forgetting to use it.

>
> For pins that are swappable, I will change the schematic to simplify
> the layout.  By swappable, I mean any pins that can be exchanged for
> same function.  For examnple, a hex not gate has 6 inputs and 6
> outputs that can be used for the same purpose.  swapping gate 1 for 2
> may lead to simpler layout.  Same thing for microprocessor register
> pins (non-dedicated ones, of course).  Headers are another place
> where you might be able to move things around to simplify layout.  I
> guess PLDs are the ultimate case.  I bop back and forth between the
> schematic and board swapping things around, often to significant
> improvement.  Clearly, there are times when you dont want to
> complicate programming but who cares if a function is on port B pin 1
> or 2, for example.  Its kind of a pet peeve of mine that chip
> designers don't always consider layout complexity when they assign
> pins.  Compare AVR vs midrange PIC in system programming pins, for
> example (AVR got it right).

Pulsonix allows 'swappable' pins and gates to be swapped on the PCB, and the
schematic may then be back-annotated.

>
> By the way, I also put SMDs on the "solder" side when doing mixed
> TH/SM layouts to avoid vias for boards I'm making myself.  If it
> prevents a drill hole, it is good.  But then if I'm using a board
> house, I dont care, so viva las vias!

I have to put SMDs on the underside, as all my boards are single-sided. I
really ought to start making my own DS boards.

Leon