So, here’s something I’ve been meaning to write up for almost a year: how to build an Arduino-powered interface to get data from any real-world, analog sensor into an iOS device using the mic pin on the 1/8-inch headphone jack. Meaning: a simple, cross-platform solution for data acquisition on your smartphone with *no* proprietary hardware or jail-breaking required. Sound awesome? It is.
Of course, this solution is about a year old (demo’d at Maker Faire in September 2010) pales in comparison to, say, the recently announced Android Open Accessory initiative and the Android Device Kit. Also, there are similar solutions out there that are better-designed and better-performing. (See, for example, Project HiJack by a team of researchers at the University of Michigan.) In the end, I put this page together to show how to do this data-through-headphones thing using stuff DIYers have lying around, like an Arduino.