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I'm trying to reverse engineer a piece of electronics that seems to be using ~1Mhz differential phase shift keying to send a signal over a 2-wire line that's also used for low-voltage power.
So newbie question here, but how do I both encode/decode a PSK signal? In terms of do I need to build a custom circuit to do it (I've found diagrams of such)? Or are there cheap/small chips that will do this for me? I ultimately need a micro-controller both reading and sending the signal.
WHat you call BPSK could be also what was commonly called Manchester code. This was used in single ended and differential mode for long hauls and depending on idle data codes, there were several types. where phase would invert on a Mark (1), Space (0) or on a transition.
If so, you need a clock sync, phase sync (mark/space/invert) depending on modulation method used and then a byte sync UART and then a frame sync if synchronous payload.
Consider this solution. http://www.intersil.com/data/fn/fn2951.pdf I used to design discrete versions decades ago.
One approach for decoding phase-shift keying is to delay the input signal by approximately a bit time, rounded to the nearest half phase, and either "xor", "and", or multiply that signal by the original, and then filter the result. This will yield a relatively nice output, even in the presence of noise which would disrupt counter-based approaches. The biggest limitation is that it requires that one have a good means of delaying the input signal.
A person could encode data as BPSK by sending the binary data to one input of an XOR gate, and connecting the other input of the XOR gate to a carrier oscillator (perhaps a 1 MHz square-wave oscillator). The output has lots of harmonics, but perhaps that's OK when transmitting over a differential pair of wires.
Decoding is a little more complex. I bet someone has already figured out how to do most of the decoding in software with a little 16 MHz microcontroller. (Excellent question; I hope someone else has a better answer.)
