[time-nuts] measuring currents on USB powered devices

[Patrick Murphy]

The unit I linked to below does support isolated power to the test unit for
those lower power, higher precision measurements. Not all of them do. True
that if you are looking for something to calibrate, these are not for you.

R/

-Pat

On Wed, Dec 4, 2019, 6:19 PM Hal Murray <hmurray at megapathdsl.net> wrote:

>
> jimlux at earthlink.net said:
> > What would be great is if there were some USB "thru" pod that measured
> this
> > and reported the data over a USB interface (recognizing all sorts  of
> > isolation issues that are possible), so I could plug the USB power  "to"
> the
> > beagle board and the USB power to the RTL-SDR, and log them both.
>
> I don't know of anything like that.  Please let us know if you find
> something.
>
> One item to add to your list.  I don't know about Beagles, but Pis are
> sensitive to not-enough voltage on the power input.  I've seen various
> stories
> about flaky operations going away when power was cleaned up.  The typical
> wall-wart for a Pi is spec-ed at 5.25V rather than 5 and you can get USB
> cables with fatter power wires.  The sense resistor to measure current
> adds to
> the problems.
>
> I have one of the little USB in-line meters.  You could point a camera at
> one
> of them and OCR it.  That would solve your isolation issues. :)
>
> --
> These are my opinions.  I hate spam.
>
>
>
>
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