USB power supply

[defred]

Maybe already asked, my MB64 is a simple one (including 1 CORE, 1 AIN, 1 DIN modules, no LCD), What I want is to have an USB power supply in addition to the normal wall adapter. My idea is that when I have no power at all, I still can use my mbox with my laptop using one of the USB port of it.

Is that possible ? I found the Usb female connector, but don't know if the 5V provided by USB is enough for this type of MB64.

defred

[smashtv]

Heya Defred!

The USB spec says this (roughly):

The USB 1.1 specification allows a device to draw a maximum of 100mA (at 5V) from a USB port during configuration.  

When the device initializes and communicates with the PC, it may request to draw up to 500mA maximum.  

This is possible ONLY if the device communicates over the USB port AND the power is available from the port.  

Thus the maximum _guaranteed_ current that may be drawn from a PC USB port without communications over the USB bus is 100mA.  

Most USB ports have limiting circuitry to enforce this current limit but some do not.  This means that on -some- machines you can get 500mA just by hooking up to the power lines.

So if you can reduce your total current draw to below 100mA (hard to do with potentiometers eating a bit of current) -or- if your laptop gives up 500mA without current control, no problem.

Keep in mind that the devices specify how much current they want during configuration, this is software/OS work around for machines without current limiting hardware on the ports.  So it is entirely possible to damage a machine by pulling too much current (over 500mA) through the port if the PC completely relies on the OS to control power management instead of hardware that actually senses the power load at the port.

Best!

SmashTV

[defred]

ok thanks a lot, that all I need, I'm going to check for USB 2.0 spec, and my toshiba USB spec, and try to find out !

dF