[gpsd-dev] GR-701W hangs on Pi-3

Gary E. Miller gem at rellim.com
Fri Jun 3 07:43:17 UTC 2016

Yo Hal!

On Thu, 02 Jun 2016 22:30:23 -0700
Hal Murray <hmurray at megapathdsl.net> wrote:

> oliver at mutability.co.uk said:
> > Do you trust your power? The Pi 3 is even more picky than the Pi
> > 2.  
> Thanks.  That could be the problem.  Meter says 4.8V.  I didn't get
> out a scope to look for dips below that.

I have heard that 4.8 is about as low as you can expect a Pi to fully
> gem at rellim.com said:
> > Everyone should have a USB V/A meter, they are cheap.  Here is one
> > for $6:   
> Beware.  Inserting a current meter will actually drop the voltage you
> get. You should probably get a real meter to see if the USB meter is
> showing the high side or low side of the current measuring resistor.

And what do you call a 'real' meter?

Any modern meter should have a really, really, small drop resistor.
But, a good question.  I'll open up a few of my meters to check.

> > The Pi people say 2 amps is not good enough, they recommend 2.5A.   
> That depends upon the stuff you plug into your Pi.  With a regulated
> supply, it doesn't help to have one with a higher current rating.  It
> might run cooler.

Yes, but overkill in a power supply is always a good thing.
> In theory, each USB port can ask for 500 mA.  I don't know how much
> the Pi will give out.  Then you can plug in a HAT...

Yup.  The Pi has 4 ports, that is 2 A right there!

Too much to think about, that is why I use the meters.

> Adafruit says their wall wart style power supplies targeted at the Pi 
> actually set the output voltage at 5.25 to give a little more room
> after the end of the cable.

Good idea.  And the Qualcom Quick Charge go up to 9V, and more.

> > 28AWG is 0.064 ohms per foot.  Double that for out and back to
> > 0.128 ohms/ft of USB cable.   
> 0.128 * 3 * 0.7 is 0.268 V.  So if you start with 5V, you will be
> under 4.8.
> Adafruit also has 6 inch cables.  :)

I like my Tronsmart 20AWG cables, and I keep them as short as I can.

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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