Where do I find USB power specification?

[Ol' Duffer]

Have a device that powers/recharges itself from USB port.
Yes, it's an MP3 player. Want to use it where there won't
be a computer to plug it into, and will probably need to
make my own power converter. Where can I find information
about voltage, current limit, pin assignments? I suppose
I could buy one of the auto/air adapters and dissect it,
but would rather have the exact specifications, not just
someone's interpretation. TIA.

 

[Charles DH Williams]

Where can I find information
about voltage, current limit, pin assignments? I suppose
I could buy one of the auto/air adapters and dissect it,
but would rather have the exact specifications, not just
someone's interpretation. TIA.

Try:

http://www.usb.org/developers/docs

Charles

 

[Ian Stirling]

Have a device that powers/recharges itself from USB port.
Yes, it's an MP3 player. Want to use it where there won't
be a computer to plug it into, and will probably need to
make my own power converter. Where can I find information
about voltage, current limit, pin assignments? I suppose
I could buy one of the auto/air adapters and dissect it,
but would rather have the exact specifications, not just
someone's interpretation. TIA.

5V current limited to 500ma. (polyfuse is popular)
Technically, the device should limit its current to a low value until
it's talked to the hub and made sure that the hub can supply it.
Most don't.
I've got a Nokia charger that is simply a resistor.

If you have a (regulated) 5V supply, then all you need to do is to
dissasemble a USB cable, and connect it up.
However, the ready-made cheap solution is to purchase a small powered
hub.

 

[Ol' Duffer]

5V current limited to 500ma. (polyfuse is popular)
Technically, the device should limit its current to a low value until
it's talked to the hub and made sure that the hub can supply it.
Most don't. I've got a Nokia charger that is simply a resistor.

If you have a (regulated) 5V supply, then all you need to do is to
dissasemble a USB cable, and connect it up. However, the
ready-made cheap solution is to purchase a small powered hub.

Sounds like I came to the right place. Thanks.

 

[Hal Murray]

Sounds like I came to the right place. Thanks.

I've seen a URL for a wall-wart type gizmo that had a USB
connector - market was charging cell phones.

Try googling for >USB travel power< and things like that.
http://www.xpcgear.com/usbtraveladp.html

The hub may be cheaper.