I am using an Android tablet to talk to an Arduino board in a project which will need to run for many hours. It is all being powered off one lead acid 12V battery.
I would like to run the Android off its own power line so I would have the D+ and D- and GND connected straight to the Arduino and the power coming from another reg (of course both using same ground). This is to ensure that I can send enough current to power the Android.
But I also want to have a switch (maybe a FET or even relay or what not) in between which can cut off the power all together to the Android and still maintain a data connection. So that I can even further save power by running the Android to a lower power threshold until I begin charging it.
Is this possible?
Best Answer
It is not unusual to have a USB device draw its power from a source other than the USB connection; such a configuration is called "self-powered" and the device's datasheet will give the exact schematic, components, and sometimes even PCB layout to make such a thing possible. It is resistances placed on the D+ and D- lines that announce presence rather than any connection to the 5V line.