Fw: Low-loss USB cables

[Gary E. Miller]

Rsending without the image as the list server does not like images.

Yo Eric!

On Thu, 2 Jun 2016 17:04:24 -0400
"Eric S. Raymond" <esr at thyrsus.com> wrote:

> Interesting.  Take a look at this, published just today:
> 
> http://www.catb.org/esr/trackman-conversion/  

I saw that.  All that work to avoid a PS/2 to USB adapter in the open?

> As you can see, we appear to have had problems with signal dissipation
> between the adapter microboard and the host hub.  

And yes, those long USB cables are dangerous to your sanity.

I also bought a bunch of 6 footers when they first came out, I never use
them anymore.

> It would be really nice if I could add something like "In order to do
> the in-case version of this mod with a 6-foot cable, you need the 
> cable to be XX AWG with YY cable-quality features."  

Easy.  20AWG is 0.010 Ohm/foot.  Double that for out and back to 0.020
Ohm per foot of USB cable.

So a 6 foot USB cable is 0.120 Ohms out and back.  2 Amps over 0.120
Ohms is 0.240 Volts.  So 6 foot OK for 1 Amp, but not 2 Amp.

Stay at 3 feet for the RasPi, even with the 20 AWG.

Simple: Eat In Restarant, PIE  
    E = IR  and P = IE

This is why Qualcom is pushing Quick Charge that Pushes 9V (potentially
more) out of the charger.

> I'll cheerfully buy one of these (and expect LF will just as
> cheerfully pay for it), given how sensitive the Pis in th test farm
> are to undervoltage problems. I expect Phil will want one too, he has
> run into related problems maintaining USB equipment in industrial
> controls.  

And you will have the same experience I have had.  You show it to 
people and they don't get it, until they "really need to*.

> Do you have low-loss USB cables to recommend?  

I'm happy with Tronsmart.  They can also be pretty cheap if you buy on
ebay and wait for the slow baot from China.

With the meter you can test them yourself, and give the crappy ones
away to enemies. :-)

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
	gem at rellim.com  Tel:+1 541 382 8588



RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
	gem at rellim.com  Tel:+1 541 382 8588
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