[Nexus 7 Original Development] br0adband:
It's pretty simple and you need two parts:

1) A microUSB cable that you're free to splice

2) A charger that puts out 5V and 2A solid, it can be a 2.5A but that's about as far as I'd recommend, it won't make any difference in the long run since the device is only going to pull the amperage it's capable of - voltage is pushed to a circuit and so overvoltage can destroy/kill hardware while overamperage is really not an issue since the device will take what it requires and nothing more

As noted, the Nexus 7 seems to not pull more than 1 to 1.1 Amps when it's charging off the factory 2A charger, and that's also using the Asus factory microUSB cable as well. Some devices actually charge at different rates based on the cable; the original Nook Color and the Nook Tablet from B&N are such devices, so is the original Kindle Fire: they would charge at a lower rate when using generic microUSB cables but if you used their factory cables they'd charge faster because of circuitry in them that detected which cable was being used.

With the Nexus 7, once you have those two parts to making a homemade 2A charger (that won't charge at 2A, at least not the Nexus 7, go figure) here's what you do - it's not all that complicated but I like to provide an abundance of details in the process so, this is all important stuff you're about to read so make note of it:

- cut the USB end off the cable (the computer USB port end)

- take off about an inch of the outer insulation (the traditionally black PVC coating)

- remove the shielding which is typically aluminum foil

- you'll have 4 conductors: green, white, red, and black

- take the green and white conductors and remove enough insulation so you can twist/solder them together - that's the key here: those are the data lines and they need to be shorted by connecting them together

- now remove enough insulator from the red (positive) and black (negative) conductors as required

- cut the end off the cord on the AC adapter and make 100% sure you know for an absolute fact which one of those leads is positive and which one is negative, this is a major point obviously - some adapters use a "marked" conductor cord which means one of them (positive or negative) has either a white or colored striped on it, or a dotted white or colored stripe, or even the insulator itself has notches or ribs or grooves in it to differentiate it from the other conductor. Unfortunately there is no "standard" for this so you have to test the adapter before you complete the cable so you know for sure that you're connecting positive to positive and negative to negative

- when you're absolutely 100% sure which one is which, splice the positive from the adapter to the positive on the USB cord (that's the red insulated conductor) and then do the same for negative from the adapter to the negative on the USB cord (that's the black insulated conductor)

- when you're all done with the actual wiring, and before you actually seal up the connections (explained below) you should test the adapter/cable right then and there so you have proof it a) works and b) the connections are matched properly (positive to positive, negative to negative, and the data pair is shorted properly). My suggestion right here and now is to find a device that charges with a microUSB cable that isn't the Nexus 7 just in case something goes wrong - I'm not saying something will I'm just being cautiously optimistic. :D I have an older Nokia phone that I use for testing in such situations, and when I finished my cable I plugged it in and... nothing. Why? Because the adapter cord on the one I have uses a ribbed/grooved conductor and I thought it was for positive, turns out I had it backwards (again, there's no actual standard for this so you have to test to find out for sure). I simply undid the connections (untwisted the positive and negative wires) and swapped them, reconnected, retested, and the phone fired right up in charge mode (it was off, of course, since I haven't used it in months)

- now that you're done with the working connections you'll need to wrap or insulate the green/white connection alone, the positive connection alone, and of course the negative connection alone. Some people use simple black electrical tape (which is what I did), some people get really professional and use some heat-shrinkable electrical tape (which you wrap around the connections then hit it with heat from a match or a heat gun and it shrinks and solidifies permanently), and so on. Basically just "protect" the newly formed connections so that they remain connected as made and don't come into direct electrical contact with the other two - that would be quite bad indeed

After that you're pretty much done, plug the working cable into the Nexus 7 and it should go right into charge mode (or show charging on the battery widget in the notification bar) without any more issues. You may note that the Nexus 7 will get warm on the back left side (the area under the "s" in the word nexus on the back) because that's where the battery is and when it's being charged from a proper charger it'll get warm since it's pulling a full amp - when it charges off a USB port it pulls 500-750 mA which is the design limit for USB 2.0 ports. The full amp it'll pull from this charging rig will definitely get it a bit warmer and it's perfectly normal.

Hope that's enough info... :D

EDIT:

I just realized I posted all that in the Paranoid Android thread, which I'm sure isn't a huge massive problem but it's a huge massive post not directly related to the ROM itself so I apologize for that... :eek: