Various energy harvesting and control techniques are used to power and control electronic accessories from the audio output channels and microphone input channel of mobile digital devices while preserving audio input and output functionality. One technique uses one of the stereophonic audio channels to generate power, and the other in conjunction with the microphone jack to enable bi-directional communications while preserving audio input and output. Another technique allows a low powered electronic accessory with bi-directional communications to be supported while simultaneously supporting audio input & stereo output. These techniques facilitate the ability to play music, narration and instruction and to receive oral responses and instruction with no perceived loss or gaps, even while using the audio jack of a mobile digital device to harvest energy and bi-directional communication.