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'[EE]: Wirewrap ?'
2000\07\06@014958 by marius bratrein

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For those experienced wire-wrappers:

Do you use thicker wire for the supply lines (vcc, gnd etc) than the
regular wire used for signals ?

I am trying to eliminate noise sources on my (wire-wrapped) board, and I
am afraid that my suppoly lines are switching to fast for the wire I am
using.

Thanks

Marius

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2000\07\06@023514 by David VanHorn

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At 01:49 AM 7/6/00 -0400, you wrote:
>For those experienced wire-wrappers:
>
>Do you use thicker wire for the supply lines (vcc, gnd etc) than the
>regular wire used for signals ?
>
>I am trying to eliminate noise sources on my (wire-wrapped) board, and I
>am afraid that my suppoly lines are switching to fast for the wire I am
>using.

Star your power and ground for anything that really eats current.
Ideally, star all, but that can be a mess.
What you can probably do, is run a power and ground pair for a section, to
a bypass cap, and from there to the chip(s)
Nothing you do in wirewrap is going to be ideal.

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2000\07\06@053559 by fernteix

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Hi Marius,

Wire wrap is to add lots of inductances and resistances  in a circuit full
of fast pulse generators applied to supply lines and ground lines.
Please read an article of B Chambers:
www.channel1.com/users/analog/noise.html
Regards

Fernando



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2000\07\06@055257 by Thomas C. Sefranek

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marius bratrein wrote:

> For those experienced wire-wrappers:
>
> Do you use thicker wire for the supply lines (vcc, gnd etc) than the
> regular wire used for signals ?

Yes, but it is NOT for noise reduction.
Eliminating voltage sag for short duration pulses is the duty of the bypass
caps.
The average voltage drop in the wire is a function of the wire size.

> I am trying to eliminate noise sources on my (wire-wrapped) board, and I
> am afraid that my suppoly lines are switching to fast for the wire I am
> using.

I hope you are NOT switching the power supply lines.
I have wire wrapped boards over 100 MHz with special WW coax,
so "fast" is probably not the problem.

> Thanks
>
> Marius
>
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2000\07\06@063139 by Arthur Brown

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This is a Question that is often asked All the recent stuff about Noise in
power supply applies here as well but with wirewrap there is a few extra
precautions needed

Regards Art

{Original Message removed}

2000\07\06@091332 by Bennett, Matt

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When I'm being extra careful with wire-wrap, I try to use a ground plane
perf board (pretty expensive, though).  Otherwise, the best method I've seen
is to use old desoldering braid for the power busses, staked down with
vector t68a pins, and then tinned.  I've also soldered bus-wire to the t68a
pins to make power busses- which makes it easy to add capacitance, I just
add it to the bus- wires.  Here's a link to a picture:
<http://web.hazmat.com/~mjb/projects/picsonar/top_circuit1.jpg>  You'll
notice that there are 2 power busses on a ground plane board- this circuit
used +5, -5, and GND.

I try to use open machined pin sockets so that I can solder the decoupling
caps to the bottom of the socket.

Matt Bennett

{Original Message removed}

2000\07\06@091959 by Stephen B Webb

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> Do you use thicker wire for the supply lines (vcc, gnd etc) than the
> regular wire used for signals ?
>
> I am trying to eliminate noise sources on my (wire-wrapped) board, and I
> am afraid that my suppoly lines are switching to fast for the wire I am
> using.

I'm not sure how fast your supply is switching -- in my experience with
noise problems & wirewrap it was the signal lines that were causing the
problems.  Put a scope (if you've got one) on various lines to see where
you aren't getting a clean signal.  Plan on re-routing your problem wires
to avoid crosstalk.  (avoid long parallel runs of wire if possible)

You could beef up your supply lines if you are switching really fast /
drawing a lot of juice.

-Steve

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2000\07\06@092410 by Ralph & Helene

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Marius-

Your best bet is to use a proto pc board that already has power and ground
bus fingers etched on with room to insert your wire wrap sockets. This would
be a far better approach than using a bare perf board and wirewrapping your
power and ground the same as the signal lines. Check Digi-Key or Mouser or
your local electronics emporium. The boards are manufactured by Vector as
well as others. Then just solder a short lead from your power and ground pin
to the appropriate bus. Bypass caps should be handled the same way -
soldering short leads.

Ralph
{Original Message removed}

2000\07\06@142610 by jamesnewton

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Given a choice between your chips not agreeing on where ground is and on not
agreeing on the supply voltage, its better that they agree on ground. That
can help a bit with noise problems. <GRIN>

A) Loop around the post then solder BIG FAT SOLID CORE wire for each chip
directly from ONE central grounding post to each ground pin. This is the
star pattern Dave is referring to. Or use a ground plain board like Matt
(overrated in my opinion). On a big board, use a tree pattern of stars
connected to stars. I usually cheat and run a bare copper rod down one side
of the board and then solder the ground runs along that down to each chip.
More like most PCBs get laid out. It works.

B) Use the same star pattern, but with standard wire wrap wire to connect
all the Vcc's. This provides a slight resistance that prevents one chip from
dragging down the supply for the other chips. Place the supply post in the
center of the board to minimize the differences in distance traveled by each
wire. This prevents standing waves from developing.

C) DO NOT SKIP THIS STEP. Solder in decoupling caps with the shortest
possible lead length between each chips Gnd and Vcc. If there are two Vdd
pins, you need to put bypass caps on BOTH pins. Use ceramic NOT
electrolytic. Peter Cousens says:
A trick I use on RF boards is to have non plated through holes included for
small decoupling caps of around 100pf. I put surface mount caps (805)
through the hole and solder it on the top and bottom, one of which will be
the ground plane.

The values aren't too critical but bigger is not better. Russell McMahon
says: You want the caps to absorb well at the third harmonic of the clock...
the ARRL handbook gives these figures for series resonance (optimum
bypassing) for disk ceramics with total lead lengths of 0.5 inch.

Cap uF  Freq MHz
0.01      15
0.0047    22
0.002     38
0.001     55
0.0005    80
0.0001    165

You can think of the setup at this point as an irrigation system with level
ground and hoses from a big central supply bucket (the power supply cap) to
a bucket (decoupleing cap) next to each plant (chip) and a valve on the
bucket (the transistors in the chip) that allows water to flow when needed.
Draining one bucket won't effect the levels in the others and the force of
the water released (supply voltage) will not vary (much) with brief use even
if the valve is turned all the way on.

D) insert a small resistance in series with each very high speed signal
produced by the chips. I always leave a pad for an SMD resister at each pin
of a high frequency signal source when I make a PCB. I just bridge the pad
with a fine trace (which acts as a small resistor) and if noise becomes a
problem, I slice the trace and install a larger resistance. That is reason
number 241 for adding resistances to io pins BTW. Think of the resistance as
a way of preventing the water valve from being opened all the way. But won't
that mess up the signal? delay its propagation? reduce its level? Well, see,
even in digital electronics, signals are analog. Its a matter of reducing
and delaying a signal A LITTLE in order to decrease noise A LOT. The signal
path acts as a (very small) capacitor and the extra (very small) resistor
helps to convert the square wave of the original signal (with infinite
harmonics) into a semi-sin wave (with no harmonics). Just ask the guys who
designed the RS-232 spec. Switching speed is an evil thing.

E) use the slowest logic family that will handle your requirements.
Currently, that means avoiding ACT or F type chips unless you really need to
work at 125Mhz.

F) Separate the physical placement and power supplies for digital and analog
(and fast and slow) parts of the board. Gennette Bruce says:
Here is a simple idea that works really well to isolate noise generating
sections of a circuit from sections that need clean power - it uses just 3
diodes and 1 extra capacitor.
 In the common leg of a 3 terminal regulator you add a diode that raises
the regulator's output voltage by the drop across the diode. You then fit 2
identical diodes to the output from the regulator to drop the voltage back
down to where it would have been. Separate smoothing capacitors are then
fitted to the 2 separated outputs.

And all of that was learned from this list, has served me very well, and is
posted (along with links to much more information) at
http://www.piclist.com/../noises
or
http://www.piclist.com/techref/default.asp?url=noises

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{Original Message removed}

2000\07\07@174758 by Peter L. Peres

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I *hate* wirewrap ;-) but when I have a ground or signal problem on a ww
board I try to add more gound lines to the suspect chips/connectors.
Having 3 or 4 wires in parallel between the same points lowers the
inductivity and the ground voltages (including in ac). You may have to add
a pin line (do you call them that ?) and short the pins together to have
supports for extra wires. I have had 2A ground currents like this w/o
problems, with four wires in parallel from supply ground to switch, and
from supply ground to connector (not my idea, I assure you). I have never
had supply problems, however a fast clock problem can be cured using the
same (many wires)  method or use a small length of RG174 coax as a wire.

Peter

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2000\07\10@120216 by Daniel Hart

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A long time ago I used a plug in insolated metal strip (like a SIP) as power
and ground busses on wire wrap. Some problem with mechanical stability, but
they can be staked down, and they provide ample current flow. Good Luck, Dan

----- Original Message -----
From: "Bennett, Matt" <Matt.BennettspamKILLspamANDREW.COM>


When I'm being extra careful with wire-wrap, I try to use a ground plane
perf board (pretty expensive, though)...
Matt Bennett

-----Original Message-----
From: marius bratrein

For those experienced wire-wrappers:

Do you use thicker wire for the supply lines (vcc, gnd etc) than the
regular wire used for signals ?

Marius

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