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Smart USB chargers and current-hungry projects
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Smart USB chargers and current-hungry projects

by halley on Sun Feb 28, 2016 9:05 am

I've been preparing for a rather BRIGHT wearable NeoPixel project, and looking at the simplest way of getting clean 5V to my Arduino and NeoPixels. Aha, how about one of those USB battery packs, since it's 5VDC already regulated and they come in prodigious mAh sizes.

Oh, but then I remembered how complicated the USB standard is, to support "high current" charging. Ancient USB ports gave 500mA and stopped there. Then all sorts of tricky and occasionally proprietary standards came in, to negotiate higher power on the USB data lines. The Anker portable battery packs have some special PowerIQ smarts to sniff out the device to see whether it should stick with 500mA, rise up to 1A, or allow the device to go full-bore and suck down 2.1A.

I found this article very useful to see how the MintyBoost could *supply* power to devices which request higher power: https://learn.adafruit.com/minty-boost/icharging

What I'd like to know is the opposite side of this coin: if I wire up a female USB connector on my power-consuming device, what will I want to put behind the USB on the consumer device to ask the supply for higher power? I'm not talking about the built-in USB on an old Duemilanove or FTDI adapter, I'm dedicating a fresh empty connector for my 5VDC IN. Is it just a matter of a couple resistors or transistors on the D lines? Can my Arduino tickle the D pins appropriately? I want more powwaah.

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Re: Smart USB chargers and current-hungry projects

by adafruit2 on Sun Feb 28, 2016 3:57 pm

nothing you do will change the amount of current the simple power adapters will provide, they'll always max out. the resistors are only for telling the *device* whats available not for telling the *supply* what it wants

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Please be positive and constructive with your questions and comments.