How to read data from a 3.5mm headphone hack?

I was searching for a way to read data from a 3.5mm hack using an Arduino, but I couldn't find a well-detailed, beginner-friendly, tutorial on how to make this, at least how to wire everything and create a simple I/O code. Anyone know a good, beginner-friendly, tutorial about this topic?

PS: I don't want to use a modem like this, I to learn and make it not communicate only with iOS/Android devices.

What's connected to the other end of the 3.5mm connector?

I was thinking about using my TI-84 for testing, then move to create a remote shutter release for my Canon 60D, and after that move to more awesome stuff like interacting with iOS and Android devices.

Sent from my iPad at 1:35am

I only managed 2.7 million hits for "TI84 Serial Interface", but I still haven't got to the end of them.

My question is not about how to make my TI-84 send the information, I already know that, it's about how to wire the connector to the Arduino to read the information.

Ah! "Arduino TI84" was only 1.5 million results.

from the description of the Audio Jack Modem for the iPhone it looks like just a regular acoustic modem from back in the day (110, 300, 1200 modems). and convertor is only translating the highs and lows of the audio coming in from the iPhone to a digital signal (5v 0v).
try this link to see if it might help....
http://www.appszoom.com/android_applications/tools/audio-serial-out_ssqt.html
the reason for the four conductor 3.5 jack is because it has a microphone line to bi-directional communication.
I found the schematic at http://robots-everywhere.com/re_wiki/index.php?title=Serial_on_Android_using_the_audio_port

Thanks very much for the help. I'm going to look at that right now. :slight_smile: