OT: power & ground for wirewrap boards

From: Loboyko Steve <sloboyko_at_yahoo.com>
Date: Mon Oct 22 00:35:26 2001

This sounded like overkill to me.

Best thing to do, is to have a WW board with pads and
busses. I've had no problems using ordinary 30 ga WW
wire for power and ground following these rules:

0. ALWAYS use "modified wrap" with one turn of
insulation as a strain relief.

1. No "christmas treeing" power from one chip to the

2. 0.1-0.01 uF bypass caps on EVERY chip. Especially
if you use HTTL or TTL instead of LSTTL. Straight TTL
draws frightening amounts of current at the instant of
a switch.

3. No more than 1" from bus to chip on the +5 and GND.

4. Use ONLY machine tooled sockets. I like Jameco's,
they aren't the best but they are good, inexpensive
for what they are, and not surplus, and therefore work
(and look) consistently. Gold on the "cup" is
important-I don't think gold plated pins is as
important if you are wrapping correctly. Yeah, I know
side-wipe sockets are cheaper - but how much is your
time worth. If you are reading this, quite a bit, I'll

5. _Never_, _never_ reuse a wire wrap wire if you make
a mistake and unwrap it - even if you "just started".
It will definitely break, if not now (and gum up your
tool), maybe later, when you'll have to find it in a
jumble of hundreds of wires. Or worse, a bare piece
will float around on your board.

6. It's nice to do the +5/GND in another color, and do
it all first.

If you don't have a plated board, I would run 16 ga
_solid_ wire up and down parallel to the chips, power
them, and work from that. You can tie them to the
board with WW wire from the top if you can't solder

I've seen WW style guides that say, "no wiring under
chips". I don't understand this. wiring across chips
brings noise from crosstalk down and shortens the
wiring considerably, also desirable. It looks visually
messy, but it looks good electrically on my scope.
Keep the wiring "short", but NEVER, NEVER "tight".
There should never be mechanical tension on any wire.

If you have a plated board (and have no intention of
reusing it), I have no problems soldering discretes to
the board, wrapping resistors, and then tack-soldering
to them to permanently connect them. Using headers
(expensive for some reason unless you know where to
find them), and sockets is extreme.

Don't make mistakes - be methodical. care in the
beginning will pay off with few or no nightmares in
the end. Check for mistakes _often_ and use a VOM with
a continuity tester to buzz out connections. You have
to get used to working backwards (the chips are
"backwards" looking from the bottom up compared to the
pinouts in a book). I don't find this kind of work the
kind where you can spend a 1/2 hour here, and 1/2 hour
there. Unless you are a wizard, no TV or radio for

Instead of the smoke test, use the VOM to power the
board (with expensive chips pulled), red lead to +5,
blk to ground. On a medium complexity board,
resistance should be 100-500 ohms. I have yet to hurt
any TTL chip doing this, because the current is so low
on a modern meter.

Using these techniques, I've gotten 4004, 8008, and
8008 boards of 15-30 MOS and TTL chip complexity in
about 5 x 8" boards, running at decent speeds, to work
(first crack in some cases!!) and have good clean
signals (see 8080geek.freeservers.com).

I don't do this professionally, I have an English
degree, but these statements come from experience.

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Received on Mon Oct 22 2001 - 00:35:26 BST

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