The prototype iPhone payment system Square, currently in testing at a trendy clothing store in NYC, has been generating a lot of buzz for the past couple of days. What caught my attention was its use of the mini jack as a communication port. Often overlooked as a means of transferring data, the microphone/audio port on the iPhone is accessible from the standard iPhone SDK. If you’re curious about using the mini jack port, the hardware chapter of the book iPhone Hacks has a number of hacks that utilize the the mini jack for uni- and bi-directional communication.
In addition to magstripe readers, IR remotes, modems, and keyboards, the mini jack is suitable for building almost any low-speed peripheral requiring bidirectional communication using inexpensive components. Since the release of the v3.0 SDK the iPhone development community has been excited about the possibilities of the iPhone doc connector. However, using the mini jack over the doc connector not only shaves off some manufacturing costs, but by using a standardized connector the peripheral can be used by other devices like, for instance, the OLPC XO.
In the Maker Shed: