P
Paul
Steve said:
Audio needs nothing special. It is low frequency. You can experiment
with audio, and try different cabling schemes, until you achieve a
desired result. So that isn't too demanding, and is something
you can play with until you get it right. You could start with
twisted pair, for example (signal plus ground twisted a couple times
per inch).
Data communication is more unforgiving. If you had access to error
counters, you could use those, to determine whether your cabling
scheme was marginal or not. Without some kind of instrumentation
running, it would be hard to tell whether your solution was
working well or not. (And I don't know enough about Windows
error counters, to tell you how easy it is to access any info
like that.)
USB and Firewire cable have both a characteristic impedance and
some good shielding. You'd need to find some specs for the cabling,
to see what characteristic impedance is used. The idea with
transmission line cabling, is to maintain the same impedance from
end to end, then terminate the endpoints properly. Impedance can
be measured with a TDR, a network analyser, or simulated with
certain commercial analog simulator software.
For an example of a fairly unique interconnection method, this
kit consists of a PCI card with Firewire and USB chip on it.
It also has a ribbon cable, and the ribbon cable carries USB2 and
Firewire signals, to the 5.25" bay. Which means, they found some
pattern of grounded conductors, and signal lines, which matched
the required impedances well enough, to get away with it. All the
other kits I've seen, use the kinds of wiring you got with your
kit.
Koutech FireWire 1394a+USB 2.0 Combo Front Panel, Model KW-F7002V
http://www.newegg.com/Product/Product.asp?Item=N82E16815104205
So, at least a planar bunch of conductors appears to work. The
DSub you talk about, though, wouldn't have a controlled impedance,
if you just used a bunch of wires arranged randomly in space. The
wires need to be arranged in a way, such that a local ground wire
or plate, has more influence over the wires, than distant objects.
The easiest way to do this, is to use the wires that came with the
kit, connectors and all. The second easiest thing to do, is find
wires of a similar type to the ones in the kit you got, then chop
the heads off and do whatever you want. The main thing to remember,
is that the "wire dress" should be maintained as well as possible.
In other words, if you cut open a USB cable, you'll notice there is a
certain arrangement of the wires, and of shield foils and the like.
What you don't want, is extended lengths of loose, dangling wires
at the end of the cable, as that creates a "reflection" and causes
data errors. At high data rates, it can be pretty hard to
fudge a cable assembly, and get away with it. Your max uncontrolled
stub length could be 1/2" or so. Making your own cables and being
that neat and tidy, could be pretty hard to do.
To give you an example of what I'm talking about, have a look at
this Asus cable assembly. There is a 2x5 female on the end of the
cable. The visible wires, as they enter the 2x5, are about 1/2"
long or so. The rest of the cable maintains its shielding, and
all internal foils are intact. Only the 1/2" of loose wire
near the 2x5, is the only less than ideal part of the cable
assembly. If you build your own cable assemblies, and
soldered them to a DSub, you'd want your wire dress to be
controlled like the Asus assembly.
http://estore.asus.com/images/14-000500020.JPG
You might also notice, that nobody makes SATA cabling with loose
wires showing. SATA signals are fast enough, that hand made
cabling is not a viable option.
Frontx.com is one source of bits and pieces, suitable for some
of the things you are trying to do. For example, the CPX-110
takes a 2x5 standard Intel FP_AUDIO header, and gives you a
headphone and microphone jack at the other end.
http://www.frontx.com/cpx110.html
You can also see on this page, that they have USB and Firewire
cable assemblies. Note that there are not consistent standards
for motherboard headers, and not all Firewire headers use a
2x5. There were some in the past that used 1xN style connectors.
http://www.frontx.com/order2.html
Frontx also sells plastic shells, so you can use a different
format for the motherboard header pins. For example, you
could buy a Frontx "Firewire to 2x5" cable assembly, pull
the wires out of the 2x5, and stuff them into a 1x8 plastic
shell. So Frontx has an interesting set of component parts,
for arranging wiring. The end result might not be as convenient
as using a DSub, but nobody said this would be easy...
http://www.frontx.com/order_c.html
Rather than use a slim computer case, plus a bunch of stuff
arranged outside it somehow, I'd probably just buy a regular,
nice looking computer case, and arrange all the components in
that. Then there is no wire clutter, and you may be able to
use the wiring that came with whatever you bought. It probably
voids the warranty on the slim computer, so I suppose there
is that to consider.
Paul