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USB Answered

i was wondering......i know computers can give electricty through USB, but can they recive it through a USB port?

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westfw (author)2008-11-17

Connect up 110V to your USB port, and I predict your computer will receive enough electricity to cause it to cease functioning properly!

More seriously, a USB "host" is only supposed to source power, and a typical host (eg a desktop PC) has power requirements (100+ watts, several voltages) that it cannot get through the USB port (which is limited to 500mA, or about 2.5W)
Now, a USB "device" can certainly be a computer in its own right, and still be powered from the USB host, as long as it consumes less than 500mA. There are some pretty impressive computers that fit that profile, but a full sized laptop or desktop probably won't.

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hypermon (author)westfw2010-05-13

first of all you said up to 110 v volts is potential energy while amps is current i dont know if you just messed it up accidentally but otherwhise here is my reply

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Sandisk1duo (author)westfw2008-11-17

What could be done with that micro "computer"? It looks like an AVR programmer module

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westfw (author)Sandisk1duo2008-11-18

If you mean the BeagleBoard, you're looking at a 600MHz superscaler 32bit processor with 128M of ram, plus DSP and graphics accelerator with HD video output capability plus assorted expansion. That probably makes it similar in capabilities to, say, the ~1GHz Pentium-3 desktops that were near state-of-the-art about 8 years ago. You could do LOTS of stuff with it.

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Sandisk1duo (author)westfw2008-11-18

Ya, bt you can't connect a CD drive and install windows XP on it

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westfw (author)Sandisk1duo2008-11-18

You can probably connect a CD via USB, and it does run linux. It's probably also capable of running WINCE (it's not called that any more, is it...)

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westfw (author)Sandisk1duo2008-11-18

You mean other than the big $149 (for the hardware) on the referenced web page? I don't know how to get a wince lincense, or how much it costs.

Another (somewhat less powerful) example of a USB-powered board is the the Make Controller

And still less powerful, you have your Arduino

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Sandisk1duo (author)westfw2008-11-18

Make Controller ->55MHZ Maybe run Pacman on it? Arduino ->16MHZ

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westfw (author)Sandisk1duo2008-11-18

Neither the Make Controller nor the Arduino have video by default.

The original PacMan apparently ran on a 3MHz Z80 ( Wikipedia says so! ), which is rather slower than the Arduino, but also more easily attached to peripherals (like video controllers.)

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mythbusterma (author)westfw2008-11-18

and thank you for telling me how to fry a computer in less than one second thatll help next time i really hate someone

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Padlock (author)2008-11-17

Nope. Don't try it either, unless you want a burnt computer as well as maybe a burnt down house.

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mythbusterma (author)Padlock2008-11-18

thanks for the reply, they other ones confuse me :S

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Padlock (author)mythbusterma2008-11-19

I can do that too :-). The computer supplies 5 volts at 500 mA, enough to power a passive peripheral (meaning it doesn't consume vast quantities of power) like a keyboard or mouse. They supply this so all of the USB devices don't have to have batteries/power adapters to communicate with the computer, which is done so by setting the two data lines (green and white) at various states, of which I am not sure.

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mythbusterma (author)Padlock2008-12-16

that doesnt confuse me....:)

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mythbusterma (author)Padlock2008-12-23

lol im a nerd too you know :D

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11010010110 (author)Padlock2008-11-20
the USB has red and black wires for 5V supply only and white and green for data communication only *

look into a USB port on the back of a computer. the plastic thing that stiks inside is on the right. 5V is in the top and earth is the bottom. wires from top to bottom are red white green black

  • the official standard limits current to 0.1 A only. then the device can use the communication wires to request more power up to 0.5 A

most computers are not as strict and supply up to 0.5 A or more without request. in many computers the 2 usb ports that are together are limited together to 1 A and you can take all of it from one of them (if you dont take all in all more than 1 A)

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Padlock (author)110100101102008-11-21

I think the "official" standard varies from model to model. I just made a few months ago a USB relay controller, and had to build circuit that requests more power. I remember when I measured I got something like 1.2 amps from one USB port (It was on a USB PCI card, so that may have affected something.)

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11010010110 (author)Padlock2008-11-22

its just computer manufacturers that understand that people need more power and violate the standard by making their computers less strict

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Padlock (author)110100101102008-11-22

Just a question; Who set this standard?

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