[gpsd-dev] GR-701W hangs on Pi-3
Eric S. Raymond
esr at thyrsus.com
Thu Jun 2 21:43:03 UTC 2016
Gary E. Miller <gem at rellim.com>:
> > Do you trust your power? The Pi 3 is even more picky than the Pi 2.
> The Pi people say 2 amps is not good enough, they recommend 2.5A.
Gary, I've digested your remarks and my experirnce into a new section on power:
== Clean power is important ==
Hackerboards like the Pi, Odroid, and Beaglebone are picky about
getting clean power because they're designed for lowest cost. Power
regulation is expensive compared to logic gates, and this is one of
the corners they cut. Under-voltage or under-wattage can cause
failures to boot, lockups, or mystery crashes.
You're generally safe if you use a vendor's wall wart matched to the
device. On the other hand, problems may arise if you try powering
from a USB hub that isn't quite up to snuff, or have lossy USB cables.
I've had good results with a powered hub from Anker, the class act in
USB equipment; beware of going cheap here.
Unless your USB cable is really short (1 foot, or less) you also need
20AWG USB cables, not 28AWG or smaller. 28AWG is 0.064 ohms per foot.
Double that for out and back to 0.128 ohms/ft of USB cable.
Anecdotal evidence says you can run a Pi 3 on 4.8V but less is a
problem. Running headless (without a mouse, keyboard or display) abd
without a HAT, a Pi 3 will draw about 700mW, but peripherals rapidly
drive up power consumption to where even 2W isn't enough; the Pi
Foundation recommends 2.5A.
There are a lot of really bad USB cables on the market, and it is wise
to avoid the price basement here too. I've had good results with
bulk-pack 3-foot cables from Monoprice. When in doubt, apply a USB V/A
meter; Newegg has them for less than $10. Be sure your meter can do 9V
for the new Quick Charge standard.
Anything to add to that?
I'm adding one of those cheap USB V/A meters to the test farm
equipment. Seems like one of those things you'll never need until you
*really need it*.
<a href="http://www.catb.org/~esr/">Eric S. Raymond</a>
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