Groups > sci.electronics.design > #446742

Re: USB cabling constraints

From	Don Y <blockedofcourse@foo.invalid>
Newsgroups	sci.electronics.design
Subject	Re: USB cabling constraints
Date	2017-02-07 20:35 -0700
Organization	A noiseless patient Spider
Message-ID	<o7e3iu$3k3$1@dont-email.me> (permalink)
References	<o7cpr0$nno$1@dont-email.me> <o7dqs5$mg3$1@dont-email.me>

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On 2/7/2017 6:06 PM, Tim Williams wrote:
> The most often committed offense I've seen: incomplete shielding.
>
> Avoid opening the shield at all costs.  Needless to say, a cable like the kind
> with a pin header on one end is useless -- these are most often seen between PC
> motherboard and enclosure, and work only because (and only when!) the enclosure
> is metal.
>
> Connector housings are often taped over with copper or aluminum tape, which
> helps, but it's pretty cheap and unreliable.  (It can be hard to tell, because
> they're usually overmolded.)
>
> Again, needless to say -- housings need to be the metallic shielded kind.
>
> Really, this is just reiterating what's already in the standard, as Jeff linked
> -- but it's worth emphasizing signal quality, especially in regards to
> susceptibility, because this will be the single greatest cause of frustratingly
> intermittent problems, and it can be caused by something as passive as a cheap
> cable.

My concern lies beyond the "electrical specs".  An "ethical" manufacturer
(i.e., someone who actually wants to make a cable that does what he claims:
"USB2 compliant") can easily meet those.

But, he can produce something that is total shit.  That falls apart during
"normal" (what's that?) use.  Or, whose performance degrades quickly
(shields opening up from flexure).  Or, outright failures without being
unduly stressed (connections opening/wires fraying from handling).

You can also disguise a crappy cable to make it appear to be well made
("obvious" strain reliefs don't say anything about the underlying
quality of the cable; flexibility approaching finely stranded Litz wire
doesn't mean there's actually a metallic conductor contained within; etc!)

I'm looking for guidelines to present to cable manufacturers to ensure
getting assemblies that "aren't shit" (yet aren't "gold standard")
once the "form" issues are sorted out.

E.g., cables intended to see frequent mating/demating would tend to
have more stringent tensile strength requirements than those that
remain /in situ/ for most of their functional lives.   Cables mated
by teenagers probably seeing more abuse than those mated by "professionals"
(upon which their livelihood depends)

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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