I have a Sony NWD B103F MP3 player that is designed to charge its battery through a USB computer connection.
I don't always have a computer with me when I want to use the MP3 player, so I have tried to charge the battery by simply connecting a regulated 5 volts to the correct USB power pins (Pins 1 and 4, with no connections to pins 2 and 3). However, this does not work with the B103F. It seems that it is necessary to more closely simulate a USB port, presumably with voltages (or no voltages) on the USB data pins (Pins 2 and 3).
Does anyone know how this can be done, please?