Jim Lux 2022/12/11 14:03
On 12/11/22 8:57 AM, Anne Ranch wrote:
> Please read carefully
>
> I had the nanoVNASaver running - both (green) LEDs on....
> Went to do something else for about an hour...
>
> Came back and my nanoVNA is dead - both LED off
> Plugged back to wallwart and the "charge LED " is flashing...
>
> My question
>
> if the nanoVNA is running an app -
> and it is plugged to PC via USB cable
> does it quit charging the battery?
>
This is a surprisingly complicated question. USB charging involves a
negotiation between the "power consuming device" and the "power
supplying device". The "request" is typically set by a resistor between
some of the pins, although there are other schemes with actual messages.
It's entirely possible for a consumer to ask for charging and the
producer to deny the request, and then shutdown the 5V to the consuming
device, while keeping the data connection alive. That decision might be
made at the time the initial connection is made, or when the stack is
renegotiated, or any other time. The USB standard allows all of these.
Worse than that, there's a chain of these decisions all the way down
from the top level USB hub (these are all inside the PC, usually). Since
each upstream port divides into 4 downstream ports, there's a surprising
number of "layers" between the connector on the outside and the top of
the tree. Any tier in the tree can say "I'm not supplying power to
anything downstream".
Windows, Linux, and MacOS all have different ways of managing this both
in a "automatic" sense, and in a "manually control" sense.
Back a few years ago, there was sort of a separation of "high current
charger" USB (intended for phones), low power supply USB (keyboards,
mice, and the like). Some wallwarts would put out enough for "low
power" mode but not "high power" mode, so the phone would charge really
slowly.
Now with USB-C and variable voltages and powers, with 40-60 W charging
(if not more) it's even worse.
So your USB NanoVNA might *connect* but not charge. Or might have
started charging, but then stopped charging. Unfortunately, the actual
chip that's doing this in the NanoVNA isn't necessarily smart enough to
a) indicate unambiguously or b) implement retries or c) be sufficiently
sophisticated.
