Hello forum , another issue for me ! First of all I want to know if it is safe to connect external 12V power at my power jack and have the usb cable connected too. I know it automatically chooses the power supply , but is it safe/recommended ?
Yes it's safe as designed.
My main issue, the GND pin of arduino has to be connected to the (-) of my power supply as well as the rest sensors/devices ? or the external power supply (-) is enough at the jack barrel ? the power supply of arduino is the same as the power supply of sensors/devices. Its a atx power supply. Thanks !
The three ground shield pins, the USB negative connector pin, and the shell side of the external power connector are all electrically tied together on the arduino board, if that answers your question. Any external components or modules you wire to the arduino that require a ground should wire to one of the arduino ground pins.