Hey Marcos, SCENARIO 1: If your MIDI keyboard has its own power supply / cable that you can plug into a wall... then you can use any of the various cable / connection options available from Apple. For example, you can connect a MIDI-to-USB Cable or USB 2.0 cable from the back of your MIDI keyboard either to an iPad Camera Connection Kit or to a Lightning to USB Camera Adapter and then plug that into your iPad.