Somewhat related to this, several years ago I have successfully used FSK[0] to transfer data[1][2] from an AVR microcontroller to iPhone through its headphone j

Somewhat related to this, several years ago I have successfully used FSK[0] to transfer data[1][2] from an AVR microcontroller to iPhone through its headphone jack. [0] - https://en.wikipedia.org/wiki/Frequency-shift_keying https://en.wikipedia.org/wiki/Frequency-shift_keying [1] - http://www.creativedistraction.com/demos/sensor-data-to-iphone-through-the-headphone-jack-using-arduino/ http://www.creativedistraction.com/demos/sensor-data-to-ipho... [2] - https://github.com/ezefranca/FSK-Arduino-iOS https://github.com/ezefranca/FSK-Arduino-iOS