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

From: Ben Franchuk <bfranchuk_at_jetnet.ab.ca>
Date: Mon Apr 1 17:55:25 2002

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!), personally, my WW overhead isn't terrible:
> I rescued all the prototype hardware from my former employer when they
> went bust - I probably have three lifetimes worth of WW sockets. When
> I do a project, the only part I have to spend money on is the wire.

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. 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

> 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. I tried to find
> one on ePay, but they only come up occasionally (every couple of months).
> I decided to build one. I started with a couple of digital pictures,
> a parts list and a schematic. Since the board was approx 6"x9", it
> would have been somewhat expensive for a commercially-made PCB. There
> are still plenty of surplus units out there that sell used for under $50
> when they are available, so it would be cheaper to wait for a sale than
> to have a professional PCB created unless the new PCB added value somehow.
> I had the blue perfboard (from when the MicroCenter got rid of all of their
> prototyping hardware at 80% off list!), the wire and the discrete
> components. I had to purchase the LEDs ($0.65 each) and the driver chips
> (a few bucks each). Total out-of-pocket expense was <$25. I probably
> pulled about $15-$20-worth of supplies out of my parts bins.
> Construction took place over several evenings, watching the sci-fi channel,
> tacking down point-to-point connections (didn't have the vertical
> clearance for socketing the LEDs). I'm pleased that it worked the first
> time! - pictures at http://penguincentral.com/retrocomputing/retrogaming/
> under the "LED Scoreboard" link. Mostly, it's pictures of the glow of
> the LEDs, but there's one out-of-focus, flash-burned picture of the
> perfboard and yellow wire in there (the Apple QT150 has about a 24" min
> focal distance without the strap-on lens).

nice (see ps at bottom)
> The upshot was that if this were being done for anyone but me personally,
> it would have been an economic disaster. Nobody would have paid me a
> reasonable amount for that much work - it would have been much cheaper
> to go to an arcade service company and *buy* a used scoreboard than spend
> 10+ hours wiring up a board. It would have been much cheaper than that
> to wait out the next wave of offerings on eBay (which I accidentally did -
> the project took so long to complete that I _did_ pick a real one up for
> around $30, after I was 95% finished with my replica. The good news is
> that it made a nice functional benchmark to prove that mine worked).
> So I chose to trade my time for semi-instant gratification. I would
> have loved to have done a PCB, but I chose not to spend the time with
> layout tape and a blank board, and 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.

> 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?
I like the PDP-8 but am unhappy that a 12/24 cpu never hit the
monolithic chip market. Now with a FPGA I have a cpu design that is a
'what if' computer that really could have replaced the IBM PC at that
time. ( Early 1980's )

> In terms of $$$/hour, even $200 for a board set
> is cheap. In terms of a discretionary hobby, $200 is a lot to divert
> from other projects when I already _have_ a working PDP-8. With that
> kind of money, I could start trolling for a Qbus SCSI controller!

Well I don't but remember with out the proper I/O a pdp-8 is NO FUN.
While I can run a emulator 100x of times faster than the real thing it
is not the same with out a TTY chugging away on paper tape.
> Back to the initial topic, though, I'd love to get a good buy on a dozen or
> so spools of kynar-coated wire. I'd prefer an assortment of colors, but
> I'd take it in whatever I could get - yellow, red, white...
> Anyone have a lead on any surplus places that have it for a few bucks
> a spool?

While B.G.Micro does NOT have wire wrap wire it does have a few
interesting odds and ends and some of the more older chips out like 16k
dram/floppy disk controlers/8 bit cpu's.
PS. Just after I finished writing this I looked up the scoreboard and
noticed you use BG micro already.
Ben Franchuk - Dawn * 12/24 bit cpu *
Received on Mon Apr 01 2002 - 17:55:25 BST

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