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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?

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  • \$\begingroup\$ Also note that the android acts as the host. So if i need the 5v into the arduino so it knows its connected could I just run 5v from somewhere else? and leave the android disconnected? \$\endgroup\$ – user1902893 May 9 '14 at 0:18
  • \$\begingroup\$ Or even add a diode or something along the line? \$\endgroup\$ – user1902893 May 9 '14 at 0:18
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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.

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  • \$\begingroup\$ Even with self-powered devices, the ability to switch and/or sense V_USB is an important part of the Session Request and Host Negotiation Protocols introduced with USB 2.0 and USB OTG. \$\endgroup\$ – Dave Tweed May 9 '14 at 14:50

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