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Author Topic: USB Power Allowance  (Read 739 times)
odin84gk
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« on: January 09, 2008, 10:35:00 pm »

I recently became facinated with Steampunk and I wasted a few hours at work mulling over the forums. While I do not have any projects in mind, I thought I would throw in my two cents.

I have noticed a little confusion about taking USB power for a custom device. According to the USB standards, you are allowed 100mA at 5 Volts for an un-initialized device (that is the same as .5 watts). If you request more power from the PC using a microcontroller, you can get 500 mA (2.5 watts).

So technically speaking, you can take a USB cable, cut it up and only take +5 and gnd. However, you must make sure you stay below 100 mA. For example, if you wanted an easy way to turn some gears, you can take the USB power, insert a current limiting resister, and attach a pager/cell phone vibrator. The larger resistor you use, the slower the motor will turn. Now attach some gears to the motor. BAM! simple motion

-Dan

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