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how to make 5v from 2 smaller power sources?/Or bump it from 3.7v to 5v? Is there a way to make the 3.7 into 5v (amp it up) or is there a way to add two different power sources into one so they add together?
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When you put a set of batteries in parallel (wired so the + sides are together and the - sides are likewise together on the other side) the voltage of the batteries are added together as an example 1.5 + 1.5 = 3.0 volts.
When you put a set of batteries in series putting one batts + side to the others - side and the free ends are wired to the device the voltage stays the same, but the available current increases (mAh) depending on the battery size.
Is that what you're looking for?
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So now you want to know if you can take different sources and add them together.
Yes & No - The issue here is the resistance of the source so if you have two of the same (i.e. 2 - AA bats) the resistance of each is the same so it would work. If you had battery and lets say an A/C line charger the resistance would not be the same so you could over heat the lower resistance source. In this example I used an A/C line charger which is not a true DC source so it also won't work correctly in this example for that reason as well. So what do need is the same type of batteries in parallel, but you could use different batteries in series as the resistive flow would be thru both batteries. But, any series set running in parallel need to be the same.
Again, A/C line chargers are not true DC as such you must be careful in there use. Radio Shack offers adjustable voltage A/C line chargers. maybe that is what you need.
If you want more you'll need to give us some better details on what your trying to do than your classic textbook type of Q.
What I'm trying to do is get a 5 volt power to power USB objects inside the nexus 7 there are a lots ways I'm sure but I would like the most simple so other people can/will be able to complete.
Battery has multiple wires going to mother board I have been told that there are two 3.7v cells in the battery running in (?parallel or series?) @7.4v. There are two red wires running 3.7v going to the board from battery. There are others but I'm not sure what they are for.
There are lots of other place to grab power from the board like the microUSB 5v but it might not charge or might not supply 5v when charging So was hoping for another way.
You really need to talk with the Google folks. I'm sure they have a HDK/SDK kit/s for hardware/software developers. You may need to pay a fee and sign a NDA, but they will offer you help in building your project.
You state "inside the Nexus 7" I would be surprised if there was enough room to put a USB interface (directly wired) and your hardware. The correct way to do this as a sellable product or even as a BYO kit/project is to use an externally connected case (via USB).
In either case you can't quite do what you want even if you have room inside the Nexus 7.
You see, USB is not a peer design it requires a hub (unlike Apple iPhone Vs the Nexus). Apple has an internal USB hub so it can support direct USB device connections. Thats one reason they have a custom connector on their iPhones/iPad as you can access the hub connections Vs the station (host) connection. In the case of Nexus your project would have the needed hub service. Thats the issue in USB I/O.
As to power its a flat 5.1 volts per the USB standard of draw not supply! so you can't power your device via the nexus USB port (internally or externally).
Heres a good reference starting point, make sure you check the links at the bottom of the page for tons of free spec sheets Wikipedia - USB
Here's a good book on USB projects design Amazon books.
As to your battery connections of the Nexus battery. You'll need to get wiring info and loading info from Google if you decide to go that way.
If you do your own external box design you can design your own power service (battery and/or charger). I even think the Google Nexus HDK kit might even have a build box you can use as a baseline in your design. Good Luck!
http://forum.xda-developers.com/showthre...
there is room and a HUB? Yes now there is
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Brad it's best to add a comment Vs updating your Q so the thread doesn't fall apart and people can follow things.
door Dan