APK HERE root required
I was trying for a while to set up my Nexus 7 to charge while using an OTG device. This is what worked for me.
I made the cable entirely.
I used two USB male ends, a female-to-female USB mating adapter and one micro USB male end.
I converted the micro usb into an OTG enabled micro usb using the instructions below.
I used shrink-wrap to permanently affix a female-to-female adaptor to one of the usb male ends, making it female.
So I ended up with a regular male plug "POWER" plug a female outlet "OTG PLUG" and a "MICRO USB" end, which plugs in to the tablet
You could use a Y adapter and an OTG cable. You would need to cut a couple wires inside
I don’t feel like writing up a step by step, so in the simplest terms, You take an OTG cable, and splice in the POWER (BLACK, and RED) wires. You leave the data, and shield wires disconnected.
SPLICE WIRES AS FOLLOWS;
I am using a custom 4.4 rom (I do not believe this is necessary)
I am using M-Kernel a69 (I do not know if this is necessary either)
Using ES File Explorer, with "root Explorer" set to "YES" navigate to "sys/module/tegra_otg/parameters"
Find the file "tegra_otg_on_charging"
Open it using your preferred text editor, or use the built in one provided by ES File Explorer
Change the "N" to a "Y"
Save the file, (It will not save correctly if you did not turn on "root explorer" option in ES File Explorer)
Now it works for me, the OTG device will be powered by the charger, not tablet.
I have to plug the OTG device, and power in first, then hook it up to the tablet.
Sorry for the sloppy write up, usually I am very detailed and thorough... I am just not in the mood today. Maybe I will come back later, after working with this for a but with updates, and a more thorough write up.