This is a porting of the Processing library for Firmata (which, by the way, needs modifications to work with Processing 2.0, but this is another story). The library is structured as a gen_server, with code for reading and writing digital and analog values to and from an Arduino running a compatible version of Firmata; the code has been tested with Arduino Yun and Firmata 2.3 (distributed with Arduino IDE 1.5.4). The example in firmata_test.erl simply blinks the test led (pin 13) every second, and reads values from a sensor connected to the first analog pin (A0) when it changes the led status.
This implementation supports only analog and digital read/write messages.