PCB vs perfboard construction economics (was Re: "New" PDP-8)

From: Ethan Dicks <erd_6502_at_yahoo.com>
Date: Tue Apr 2 15:53:21 2002

--- Ben Franchuk <bfranchuk_at_jetnet.ab.ca> wrote:
> Ethan Dicks wrote:
> > While I can recommend a real PCB if the setup costs and the per-sq-in
> > costs are not killing you (price an Omnibus or Unibus-sized 4-layer
> > board, complete with gold fingers!)...
> Out here the only parts store is Radio Shack or wait 6 months to get to
> a larger city. Thus mail order and internet shopping works for me.

Here in a city of 10E+06 people, about all we have left is Rat Shack,
too. When I was a kid, there were lots of surplus places and new
parts places to shop at (c. 1978). They've all gone mail-order and
shut up their sales floors for cost reasons.

I do most of my component shopping online these days (BG Micro, Mouser,
Digikey, Allied...)

> With wire wrap I would spend too much time hunting for bad
> wires/connections or paying $$$ for parts. A PCB is a simple upload of
> my gerber and drill files.

Simple upload, yes, but for larger designs, it starts to get pricey
again until you make things in quanity. I did several runs of a two-
layer Zorro-II board (GG2 Bus+) - q. 100, they cost around $15-$20 each,
including spreading out the setup charges. That's with a lot of gold
(100-finger Zorro edge, plus a full 16-bit ISA edge), and a foot-long
PCB. If only I hadn't ordered that last run of boards... :-( At q. 25,
they were significantly more expensive. At q. 5, ISTR they were over
$50 each.

> > My last project is a good case-study for expense vs. time. I wanted to
> > replicate a scoreboard from a Dragon's Lair/Space Ace...
> > pictures at http://penguincentral.com/retrocomputing/retrogaming/
> nice (see ps at bottom)

Thanks. I am proud of it, even if it is a simple project. It is a one-
for-one, mechanically sound replica of the original. I did the parts
layout all from measuring digital pictures with a ruler. :-)
> > ...I chose not to pay to register a
> > demo-ware layout package so I could make a 6"x9" board.
> More like 3" x 4". Easytrax (dos) is still out there and runs fine (and
> free) if you don't need autorouting.

I think you missed my point... yes, the demoware packages let you lay
out a 3"x4" board for free. Because of existing mounting holes and
the physical area needed to contain several rows of 7-segment displays,
my board needed to be about 6" x 9". For this and other classic projects
I'm working on, 3"x4" does _not_ cut it. I am planning on things like
DEC quad and hex-height boards - measured in square feet, effectively,
instead of square inches (~0.8 sq ft - ~1.5 sq ft) To make one, it's
physically cheaper to buy a surplus DEC prototype board and WW it. To
make 5, PCBs start to look real good, even if they are $200 for a multi-
layer, gold-edged, foot-square board.

> > If I were to
> > make the new PDP-8 design that kicked off this whole thread, I'm not
> > sure if I'd get professional boards (~$200/set, in small quantities,
> > according to the designer, for a couple of 4-layer boards) or I'd
> > point-to-point it.
> Is 4 layer boards really needed?

It's handy for signal isolation, and that's the design that Bob
did the layout for. All of the professional Qbus and Unibus boards
I've worked on in the past were 4 or 6 layer designs for good reason.
You can only cram things in so tight in two layers. If you are going
to go for an integrated computer on a 4"x6" board using DIP components,
you'll be looking at 4 layers before you know it. If you increase the
size of the board and keep things under 8MHz, 2 layers (and a sensible
layout) will probably be fine. A 1MHz 6502 design will probably not
require multi-layer unless you want it the size of a pack of playing

> I like the PDP-8 but am unhappy that a 12/24 cpu never hit the
> monolithic chip market.

That would have been fun.

> Well I don't but remember with out the proper I/O a pdp-8 is NO FUN.

True. I already know how to make a front panel pulse the lights.
Driving a TTY is a lot more fun.

> www.bgmicro.com
> PS. Just after I finished writing this I looked up the scoreboard and
> noticed you use BG micro already.

Yep. Been a happy customer for years. Thinking of placing an order
this week.



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Received on Tue Apr 02 2002 - 15:53:21 BST

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