the raspberry pi is the ethernet tcp/ip webserver front-end (also means its the android/iphone way in) and it talks 'volume control language' over a serial connection to the lcduino. the pi system has an onboard hardware uart (/dev/ttyAMA0) and the arduino has one, too (2nd and 3rd pins on the 6pin ftdi vertical 'download' header on the lcduino).
here's a simple level converter that works, is super cheap, and btw, did I say that it works?
a simple cd4050 cmos chip that is half a dollar or less. the schematic comes from this link:
http://www.andremiller.net/content/rasp ... -gpio-uart
a 'shield' is made from perf board and a 26pin (strange but buyable) dual row .1" spaced IDC style socket. there is no support for shields, no screw holes or anything, so I did my best to get the one single chip to line-up on an 'available' (lol) riser connector that I'll never use or care about. I put that cmos chip *just* so, and then worried about the rest afterwards.
wire layout is simple:
the Pi board provides 3.3v via pin1 (square index pin on the Pi pcb; on my board, its the only blue wire there. (btw, don't ever cut the blue wire!)
the green wire is the gnd connection.
black and white are tx and rx (check the schematic for which is which).
the red molex connector takes the tx, rx and gnd offboard and onto the arduino system. there, you use the usual colors that the ftdi cable uses (except my green is ground; ftdi 'official' gnd is black/brown).
this assumes you power the lcduino from a nice 5v supply and you have given power to the Pi via its micro-usb connector or some other way.
that's all the hardware hacking needed! just that one cd4050 chip, some wiring and sockets and software. yeah, it needs some software on the 'pc' side
more on that, later.
