Networking: Ultrasonic communication

The goal is to create a digital communication link over 40khz ultrasonic transducers. Ideally, this should be possible for several foot ranges with no electronics beyond the microcontroller.

I successfully got an analog input reading at 80khz capable of seeing a 1 mV p-p 40khz signal (and possibly smaller). This data is read into a circular buffer and then filtered with Neil's ultra fast digital filter technique.

I still need to implement output to the transducer (very simple) and then some kind of simple channel sharing protocol to setup a bi-directional serial link.