Arduino to Android IO on the cheap (aka Poor Man’s NFC) via Dangerousprototypes.

This is a little hack that allows very low bandwidth communications in one direction for practically no cost. It’s not practical for most applications, but I thought the idea was sufficiently interesting to explore. This article describes how to implement a very low bandwidth one way communication channel between an Arduino (or any other microcontroller) and an Android device using nothing more than about a meter of magnet wire, a resistor and diode. Links to a software sketch for the Arduino and the Android source code is included.