A mobile computing device comprises a housing, a memory, a first current source driver, an audio interface and a processing circuit. The housing is configured to be held in a hand during use. The memory is configured to store audio data. The audio interface comprises a first terminal, a second terminal, and a common ground terminal for the first and second terminals. The processing circuit is configured to control the first current source driver to provide a first audio signal on the first terminal based on the audio data.