[sdiy] PCB files

[Joe Grisso]

Um. Wow.

Not to be negative, but you guys should really learn to place your
design before you route.

I understand this is your first time out, so I'll be gentle.

Yes, it seems logical to group each component by type, but this, in
reality, is bad practice. Look at other circuit boards. Take apart
older synths and hardware you have and learn from it. Usually smaller
parts such as resistors and capacitors are grouped around the larger
ICs. They're placed on the board based on certain criteria: Signal
flow, trace length, package constraints, signal integrity,
manufacturability/testability and so on.

Let me give you an example. In the case of a guitar distortion
circuit, there's usually a preamplifier, the distortion circuit, a
bypass circuit, and the output buffer in the signal path. There's
usually a power supply as well to split and/or boost the 9V wall wart
into +/- supplies or whatnot too.

Placement would go like this:

Input preamp circuitry would be located close to the input guitar
jack, distortion circuitry somewhere in the middle, bypass circuitry
close to where the pedal switch is, and the output buffer by the
output jack. Power supply circuitry is put by the power jack. All
related components: resistors, capacitors, diodes, and whatnot are
grouped according to their function around the larger ICs (op-amps,
ADCs, DACs, microprocessors, what have you).

Only after the placement was put together properly would the engineer
route the board.

In your case the VCO would have the input voltage processor, the expo
converter, the oscillator core, and the output waveshapers. While this
is audio realm, care must be taken with some layout considering the
expo converter's thermal dependencies as well as the sensitivity of
the triangle core you're laying out. You need to keep the feedback
paths short, among other things. The way I would lay this out is as
follows:

input jacks -> CV processor and trim -> expo -> relaxation core ->
output waveshapers

Then finally to the output jacks.

That's where I'd take it from here.

Nice try, sorry you're getting a lot of harsh feedback, but don't be
discouraged. The criticism, while very discouraging, can be your
greatest asset if you persevere.

I'd start over, place the design, then show the design placement with
ratsnest to the group - that would be a good point to work from. We
can give you feedback on where to move things, what trade-offs you
have to make, etc. I'd be more than happy to help.

Best Regards,

Joe Grisso
Detachment 3 Engineering

On 3/5/07, Charles Bisaillon <sdiy at oveloe.com> wrote:
> So my team mates have finished the PCB files with only few thing to fix. But
> they followed only half the PCB design guidelines from Joe Grisso that I've
> posted for them. The trace size is alright, the PCB size is alright but the
> component placement is horrible (for trace length) and they finished them
> off with autotrace and 2 layers. Check it out.
>
> http://www.oveloe.com/490/VCOpcb.JPG
>
> I have never done this before but, according to the guidelines, this PCB has
> major problems. But on the other hand, the breadboard is surely worst with
> all those stray capacitances, but experimentally, it was a bit noisy but
> really not that bad (on my 10$ cpu speaker).
>
> I am asking those of you who have experienced this before. Is this
> acceptable? Would any of you consider this good work? I really am new to
> this and thanks a lot for your help.
>
> Charles
>
>