There are quite a few 3rd party devices that attach to a smartphone's 3.5 mm headphone jack, Square's Credit Card reader, being just one of them. We will reveal the magic behind this cool innovative trick, explain how it was done and how your mobile app too, could take advantage of the headphone jack. Hijacking power and bandwidth from the mobile phone's audio interface. Come to see and learn how mobile app take advantage of a smartphone's headphone jack.

We will use "phone to phone" as well as Arduino to Android examples to demonstrate and explain this cool and innovative communication channel, and you may even pick up a couple DSP (Digital Signal Processing) basics along the way.

Presentation slides are in this file: jack.pdf Arduino sketches are in Arduino/sketch_1 (tone demo) and Arduino/sketch_2 (light sensor) Android Jack application source is Android directory.