Gerhard Fiedler wrote:

> (They use duty cycles of 1/3 and 2/3)


I used this approach a while back on a hobby project and it worked quite 
well for my needs. Extremely simple to encode and decode.

For receiving, I used interrupts driven by edge detection from the RF rcvr.

Once triggered, I counted one-banana, two-bananas until half a bit time 
transpired.  Then I sampled the incoming line.  Shifting this in 
produced a byte.

Is it the correct byte?  I used framing as follows: synchronize with 
0xAA, 0x55, byte count, data, checksum.

The 0xAA and 0x55 did duty to get the RF rcvr to play nice.  Plus noise 
had a hard time to keep up and look like that along with the byte count 
and checksum.

I was sending control data to a lighting controller; if a frame or 3 got 
lost, no big deal.  The data was sent continuously until the operator 
approved of the result. Think: operator with control watching the lights 
for correct operation.

Noise, especially when the TX was off, meant a steady stream of 
interrupts.  I dealt with this in the easiest way: a separate PIC to 
demodulate the RX line.  Only good data got sent to the main controller 
via serial data lines.

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