How does this 'back channel' appear?
Physically this is a standart USB plug:
receiver has type A socket
transmitter has type mini-B socket(?)
Its normally used to connect a keyboard, mouse,... to controll the PC (while the PC is sending the video stream the other way to the display). So, it is "more or less" a pass through USB connection.
I tried, if it is a simple point-to-point electrical connection by just applying some voltage to the one end and measuring the output, but unfortunately its not that easy. The system needs a USB host device that sets up the protocoll.
When a keyboard is connected, the computer sees the keyboard as if it was directly pluged into the computer - the wireless system does not appear itselfe. So, if I can set up two Arduino boards to communicate via a normal USB cable, I'm pretty sure a can replace the cable with the wireless system.
The below book might help you get up to speed on USB.
Thanks, but I'm not going to buy an expensive book - there must be some more information on the web. Has nobody ever tried this? (I'm a bit disappointed now, I thought the Arduino community has exploited the possibilities of that littel board far more than some blinking LEDs 