On 12/12/22 7:34 AM, Tim Dawson wrote:
5v power should *always* be available on a USB port,
Not necessarily - there are USB hubs that if they get a request for high power, and can't supply it, just shut down the power and disable that port, other than some microamps to tell if there's a unplug/plug event.
so slow charging can
happen even on a dead device. What is negotiated are faster charge rates,
so, as you noted, a dead device will need to slow charge to the point that
it can power up before it can take a fast(er) rate of charge.
(FWIW, I have never charged my NanoVNA H4 on anything *but* my laptop USB
port (no external hub - just plugged it in. Seems to work fine.)
- Tim
On Mon, December 12, 2022 9:13 am, Anne Ranch wrote:
I was going to quit this thread, but...
I left the nanoVNA running overnight , connected to my PC and I did
"shutdown" and turned the PC power source off.
Turned off the D_link power source too.
In the morning I got no LCD and no LED's.
Turned all AC power on (PC , D-Link) and run "lsusb".
Still no LCD and LED's and no nanoVNA USB device.
Unplugged nanoVNA from USB port.
Unplugged "wallwart " from AC !!!
Plugged nanoVNA to dead wallwart and - LCD came on, so did both LEDs -
BUT briefly
Plugged wallwart to AC and have normally operating nanoVNA
LCD on, charging LED on , sweep LED flashing,,,
My conclusion / opinion
in my interpretation of USB "standard operation"
...when a USB device is first plugged into its controller
it runs kind of "here I am " sequence and the controller should
acknowledge that and respond ...
How does supposedly dead nanoVNA manages to do this when plugged in DEAD
power source ?
