I am interested in making the netduino establish a BUS connection to the IPhone via the audio jack. Does anyone have any experience doing this? I have read a few things online...but I am somewhat lost.
There is a project developed by David Jurick, Adam Stolarz, Damien Stolarz that is described in the book iPhone Hacks. They use the audio jack as a Frequency Shift Keying (FSK) modem that operates at about 1200 baud. Their project interfaces with a Cypress PSoC microcontroller to convert the audio signal to RS232. Source Code can be found at the www.perceptdev.com site.
A similar project using an Arduino to convert the signal can be found here.
Another project called HiJack harvests power and bandwidth from the iPhone's audio jack.
The Arduino CPU might be able to handle bidirectional BPSK at a low enough baud rate.