I am thinking of trying to establish a bit of communication between two AVRs, using some form of inductive coupling. For starters I will be satisfied with only one-way (simplex) data.
I'd like the receiver to be as small as possible. If the receiving coil can be kept within 2-3 cm in diameter, I'll be very happy. The transmitter can be larger if needed. I only want to transfer data, not energy to power the AVR. I need 2-5 bytes data, and the inductive reach should be 1-2 cm. The data transfer speed can be very low.
I tried to Google quite a bit for inspiration on how to make the analogue frontend of the receiver, but usually end up with patent applications or other things for something irrelevant. Do you have any good pointers?
I'd like to keep it as simple as possible. Maybe even down to the pick-up coil being part of a tuned LC circuit, and then using a diode as AM demodulator. I'd like to experiment with FSK (instead of AM) if the demodulator can be made simple enough.
I am planning to use a XMega E5 in the receiver, so it may be possible to integrate some of the decoder/demodulator functionality in its custom logic module, that in turn can interface to the USART. But that can always come later. For starters I'd just like a bit of inspiration on how to make the coils and surrounding circuitry, and what range of frequencies that are suitable for this type of application. Any ideas?