Back-Powering?
Raspberry Piは、USBのmicro B端子を使わなくても、Type A端子から電力を供給できるらしい。Back-Poweringというキーワードで探すといろいろでてくる。micro Bがあると右の写真のようにごちゃっとなりやすい*1ので、無くせたら、USBハブからの配線がきれいにできるし、ケーブルの取り回しもいい。
Back-Powering; (powering the Raspberry Pi from a USB hub through the uplink/data port, single cable) Back powering is possible on the Raspberry Pi, but not advisable. Revision 1.0 boards have to be modified to back power, this is due to the 140ma "polyfuses" that are installed in the USB port circuit. Revision 1.1 boards do not need modifications to back-power, they have replaced the polyfuses with 0ohm resistors in their place. Revision 2.0 boards do not need modification, they have neither resistors nor polyfuses. It is advised that short (12" (.3 meter) or less) USB cables be used for back-powering a Raspberry Pi. Cable resistance plus connector resistance can quickly reduce operating voltages below the proper range(5.25V to 4.75V). But do note that if you do not power the PI in the "official manner", that is through it's micro-USB port, but use any alternative way (such as through the GPIO header, the test points TP1 and TP2), but also by back-powering it, you are actually bypassing the PI's input polyfuse protection device! This can have extreme consequences if ever you manage to put more than 6V on the PI, even for a very short period. As this causes the overvoltage device D17 on the the PI to trigger and short the 5V supply! Without the polyfuse limiting the current through D17, it will burn out, probably melting the PI's enclosure with it, (if you have any) and possibly causing a fire-hazard. It will probably also create a permanent short of the 5V supply! So be warned, and if you use back power make sure your hub or its PSU has a fuse to prevent this from happening. If not, add your own fuse.
以下の動画では最初micro Bにつないでから起動して、Type Aに切り替えている。
How to back-power a Raspberry Pi with a USB hub - YouTube
Raspberry Pi • View topic - Backpowering Pi with a USB hub (solved)
しかし、micro Bを使わなくても起動できるという話を聞いたので、ちょっと調べてみたい。まずはType A - Type AのUSBケーブルを買わないと！
追記：
単純にType AにUSBを差せば動いた、と聞いたので試してみたい。
追記２：
動いた。ただしType A - Type Aのケーブルの選択肢が少なく、無駄に長くて割高なのしか買えなかったので、そんなに嬉しくなかった。
*1:関係ないところがごちゃついて見えるかもしれない :-P
