4
This is an exercise in futility!
Disabling devices will make very little difference in power usage, which is mainly determined by processor load.
About the ONLY device which will have any affect is WiFi.
You should consider a Pi3A+ which has lower consumption and no USB hub or Ethernet.
2
You can’t power the Pi through GPIO, but you can power through the 5V and Gnd pins on the expansion header.
This is perfectly safe and acceptable, provided the supply complies. HATs often do this and the Foundation has compliance recommendations.
Indeed in some Pi models (including the Pi4) these are directly connected to the power connectors.
2
As far as I know, you can not disable only one USB. When you turn USBs power off, also the Ethernet port turned off. I don't know if there is a way to disable USB/Ethernet in config.txt, but in cmd line you can do it with:
echo '1-1' |sudo tee /sys/bus/usb/drivers/usb/unbind
To enable the ports use:
echo '1-1' | sudo tee /sys/bus/usb/drivers/usb/bind
...
1
No rep to comment yet, so this goes as answer.
This is generally a bad idea to use the same SD card swapping between devices, as each of them has its own configuration - despite the same system. Devices differ by on-board components id, or even might be different due to newer revision of board. I own 2 rPi 1 B+ and swapping cards is impossible due to errors ...
1
If you want for some reason (multiple captures audio etc...) You can adapt this schematic (thank's to bitluni's lab):
replace 3V with 3.3V output of raspberry GPIO 3.3G (your microphone needs to support more than 3V, otherwise adjust the resistors). You now have a MONO microphone and a TS connector (very clear drawing, the AMP part). For me, I have an old ...
1
I believe there is no audio input on the Raspberry 3B+.
You will have to find a hat to put your Piezo microphone, or go with USB…
It's difficult to make a Audio input as it requires a efficient and fast ADC to convert the signal and this is not something present on the Raspberry 3B+.
Note that USB may have latency compared to GPIO HAT based solutions.
But ...
1
By updating and upgrading it may have tried to update the settings it originally has with trying to boot from sd instead of the SSD, I would first take out the SD Card, plug it into a computer and add an empty file called ssh, then put it back on the Raspberry pi and boot. After it boots you should be able to ssh to the pi long enough for you to run another
...
1
You can use tmux for this (apt install tmux). First find a tutorial you like to get the hang of how it works generally (it is pretty popular amongst linux users and has been around for more than a decade, so there's plenty of stuff online).1
One of the first things you will learn is how to create, detach, and join sessions.
tmux new-session -s foo
Starts ...
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