raspberry pi, USB a maximalny prud z USB
http://raspberrypi.stackexchange.com/questions/340/how-much-power-can-be-provided-through-usb
https://github.com/raspberrypi/linux/issues/29
http://raspberrypi.stackexchange.com/questions/340/how-much-power-can-be-provided-through-usb
https://github.com/raspberrypi/linux/issues/29