[mythtv-users] OT: USB inductance (or other) problems with external peripherals

[Jay Ashworth]

----- Original Message -----
> From: "Marius Schrecker" <marius.schrecker at lyse.net>

> 1. Maxing out the usb connections with relatively long cables is
> stressing the USB controller and giving me garbage. I'd be better off
> restricting myself to a USB 2.0 bus to the HD-PVR and running
> everything else through other USB 2.0 bus and the powered hub.

I don't believe 1.5m busts the length limit for USB 1.1 or 2.0, but are 
you actually sure it's that short?  That's *awfully* short to be going
through a floor to a different, well, floor.

> 2. The problem is the crowded conduit. I'm getting inductance problems
> which are causing noise.
> I need to split up the cable runs with max one or two cables per
> condiut ( a pain in the *** as I'd need to rip the cellar ceiling
> apart (again).

Not inductance so much as crosstalk, depending on what else is in that
pipe. Power cabling is the only think I would expect to actually
cause a problem; the jacket thickness should be enough to protect you
otherwise.

> I' m way under the max cable length of 3-5M for USB, so whatever is
> causing it, my two guesses to the problem itself are interference and
> voltage drop.

Well, we agree on the lengths, then.  :-)

> Does anyone know about the electromechamnics of what I'm doing and can
> they shed some light on where I should start changing things?

Well, what's the fill percentage on that conduit?  For power, you don't
want to go over about 60% or so -- and I can't imagine you *could*
with preterminated LV cables; you couldn't get the plug though the pipe.

> Worst case is I'd have to abandon the whole approach and do it the
> proper way, spending the money and building a small footprint and
> SILENT dedicated frontend into the bench.

That may be more cost efficient even if you can get this to work; 
don't value your time at $0...

Cheers,
-- jra
-- 
Jay R. Ashworth                  Baylink                       jra at baylink.com
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