Groups > sci.electronics.design > #446738

Re: USB cabling constraints

From	Don Y <blockedofcourse@foo.invalid>
Newsgroups	sci.electronics.design
Subject	Re: USB cabling constraints
Date	2017-02-07 20:23 -0700
Organization	A noiseless patient Spider
Message-ID	<o7e2st$1vd$1@dont-email.me> (permalink)
References	<o7cpr0$nno$1@dont-email.me> <o7csgl$4bg$1@dont-email.me>

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On 2/7/2017 9:28 AM, amdx wrote:
> On 2/7/2017 9:43 AM, Don Y wrote:
>> Are there any rules/guidelines for manufacturing/designing USB2 cable
>> assemblies?
>>
>> Compared to the constraints on network cables and SCSI cables, are they
>> somewhere in-between?  Microphone cables?
>>
>> Or, more like ZIP cord for speakers?  :>
>
> I don't know*, but I just bought a cheap usb to apple iPod connector cable.

Note that there are different types of "<favorite_device>" cables.
E.g., you can purchase cables that are only designed for charging
while others can also support data exchange.

I've encountered many folks who bought cheap *charging* cables
and wondered why they couldn't "talk" to their <device>.

> I hadn't charged the iPod for years, (it was one of my kids). I plugged it
> in and the battery charged, before I got to down load and data I dropped it
> and the plastic shell came off of the connector. I notice the white wire had
> been heated to the point the wire melted out of the insulation, of the four
> strands! one was broken. OK it wasn't touching anything so, whatever. But

Yeah, store-bought cables are hard to repair.  Like the old WE cables
that had a thin strip of copper *foil* wound around a nylon (?) core...
attempts at soldering would just result in a "plastic" glob and a
piece of foil that kept "shriveling"  away from the approaching hot
tip of the iron!

> then I noticed two of the wires were shorted together at the pins. Looked up
> the connector and the Data+ and Data- were solder together. So, I cleaned it
> all up and put it back together. Now it doesn't even recognize the usb has
> been plugged into the computer.

Try putting ~100-200 (no more!) ohms between the data pins and see if it
will again supply charging current.

> * Well I have some clue to your question, this cheap cable has no shield,
> the wire is smaller that a #40 and there are 4 strands. I was not able to
> see any twist. Tested with ohmmeter and it all checks correct. But no long
> will charge the battery.
>
> A google search show, quality cables have a shield, the data pair are and
> power pair are twisted.

Sorting out the electrical characteristics isn't a problem -- the Standard
addresses those.

But, that leaves a wide range of "valid" cable manufacturing techniques
that range from "gold standard" through "average", "adequate", "mediocre"
and "total shit"!  :-/

E.g., it's relatively easy to make a CAT5 cable that passes DC specs.
A wee bit harder -- but easy with damn near any amount of practice -- to
make one that will also pass AC specs and "perform well" (electrically).
Quite another challenge entirely to make one that can be (ab)used normally
AND still perform well!

A microphone cable requires a bit more care -- exposing the conductors
from *inside* the shield, connecting the shield (electrically), not melting
the insulation on the inner conductors as you solder the shield, crimping
the cable "bulk" to the connector (so it doesn't fail the first time the
performer removes the microphone from the stand and walks across stage
with it), etc.

At the farthest extreme, imagine running ZIP cord to a set of speakers.About 
the only real issue is making sure you've got the polarity correct -- and
that only begins to apply if you have more than *one* speaker!  Someone could
trip over the cord RIPPING it from the connections on either end and you
can have it back in place in seconds, "operating" normally!

*Most* store-bought USB cords will meet their stated purpose (e.g., if only
spec'd as a "charging cord" then it doesn't have to also support data
transfers to be considered "good"!).  But, *many* won't be "good
investments"  :-/

Thread

USB cabling constraints Don Y <blockedofcourse@foo.invalid> - 2017-02-07 08:43 -0700
  Re: USB cabling constraints amdx <nojunk@knology.net> - 2017-02-07 10:28 -0600
    Re: USB cabling constraints jrwalliker@gmail.com - 2017-02-07 08:54 -0800
    Re: USB cabling constraints rickman <gnuarm@gmail.com> - 2017-02-07 20:37 -0500
    Re: USB cabling constraints Don Y <blockedofcourse@foo.invalid> - 2017-02-07 20:23 -0700
    Re: USB cabling constraints Robert Baer <robertbaer@localnet.com> - 2017-02-08 21:29 -0800
      Re: USB cabling constraints Kamen Lilov <kamenl@gmail.com> - 2017-02-09 14:01 -0800
  Re: USB cabling constraints Jeff Liebermann <jeffl@cruzio.com> - 2017-02-07 10:39 -0800
  Re: USB cabling constraints "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-02-07 19:06 -0600
    Re: USB cabling constraints Don Y <blockedofcourse@foo.invalid> - 2017-02-07 20:35 -0700
      Re: USB cabling constraints "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-02-08 17:49 -0600
        Re: USB cabling constraints Don Y <blockedofcourse@foo.invalid> - 2017-02-08 20:33 -0700
          Re: USB cabling constraints "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-02-09 16:43 -0600
            Re: USB cabling constraints Don Y <blockedofcourse@foo.invalid> - 2017-02-09 16:18 -0700

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