Hijacking Power and Bandwidth From the Mobile Phone's Audio Interface
The authors endow the mobile phone with a low-cost, open interface that can parasitically power external peripherals, and transfer data to and from them, using analog, digital, and serial signaling, using only the existing headset audio port. This interface, called HiJack, allows the mobile phone to easily integrate with a range of external sensors, opening the door to new phone-centric sensing applications. In this paper, they characterize the signaling and power delivery capability of the audio jack, design circuits and software to transfer data and harvest energy, and evaluate the performance of their designs. They also use the mobile phone's audio channel to create a layered communications stack that supports low-level, analog signaling and high-level, multiplexed data communications with external devices.