[simpits-tech] More on USB

[geneb]

On Mon, 15 Sep 2014, Matt Bailey wrote:

> As I understand it, there are two different situations going on here
> where inductive loads OR high voltages can wreak havoc with USB:
>
> 1. The USB device is being used in close proximity to an inductive
> load, such as a relay or motor. I have only observed this once, when I
> was activating a relay. One (and only one) of my Arduinos would kick
> offline when the relay was switched on and off (I don't recall if it
> happened on energizing, or de-energizing). The Arduino was NOT connected
> to the relay, that was being controlled by a Phidget I/O board (which
> did not kick offline). Presumably, sufficient EMI was produced by the
> arc when activating the relay, or perhaps by the magnetic field
> collapsing when the relay was de-energized, to interrupt the Arduino's
> USB connection. Your point about isolating the USB interface from the
> load is a good one, but I don't believe that is what was going on here.
>
Try it with the Arduino on a different hub and see if the problem 
persists.

> 2. The USB cable, or wiring connected to the USB interface, is near
> some high voltage AC stuff, such as 115v 400hz aircraft power for
> lighting. I have not observed this myself as I am not dealing with
> 400hz yet, but I have been told by other folks that it's a nightmare.
> My understanding is that the magnetic fields produced by the AC
> voltages in the aircraft lines pass voltage to the wires connected to
> the USB interface, delivering potentially high voltages to the device. I
> believe this would also be considered voltage via inductance, no? Or
> just general electrical noise, at the least.
>
This is only a concern if you've got a USB cable running in parallel and 
close proximity to an AC line.  If the USB cable crosses the AC line at a 
90 degree angle, you should be fine.

You'll have the same issue with ethernet if you're running it parallel to 
AC lines.

A good rule of thumb is to keep low voltage stuff on one side of the 
cockpit and AC stuff to the other.

g.
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