I'm posting here for some people help me or give me the way to take for what i want to do cause i have no idea how to proceed.
i explain :
i have my pi who is running a java server app( who handle sensor and relay), on side i have a java client app who connect by internet to the pi.
for prevent the case where there is no internet ou the init phase, i have to make my pi able to be connect by a usb cable to a pc or tablet and be recognize as a device for be able to let my client app connect via this serial (ttyUSB0) to my server app.
i hope i have been enough clear in what i am planning to do. (about the usb i have one wihout the vdd and the ground for prevent the fry risk)
how to set my pi for let be recognize as device when i will plug that usb cable ?
thanks for all who will take the time to help me ( and in case of someone start to say why use the usb and not the pin or serial blabla, cause in my project i NEED to )