Since I haven't hooked up with Bill yet to get the EFIKA, I started playing with the SRF02 Sonars, to figure out control over the i2c bus. This is what I'll be doing with the EFIKA, eventually. The interface is pretty clean - you can just request a ping, wait 70ms, then read the result, or you can poll on the result if you want, shudder. So there are just three data bytes across i2c for each ping - no self-timing or any of that.