Re: Random Correlation Detector

"Luhan" <luhanis@xxxxxxxxx> wrote in message
news:1146591446.902402.219830@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

I'm only looking for the presence of the signal. This is simple a
version of an IR photobeam that ignores other signals.

This would be used in an environment with several signals in the same
general space. In other words, I'm looking for an emitter/detector
that only responds to its own signal.

Luhan

As an interruptor with a low to moderate data rate, you can just add/sub
your incoming photodetector signal by the outgoing PRBS (pseudo random bit
sequence rather than pseudo random noise) sequence. You get a strong output
from the add/sub or you don't. If you have no return path from your
emitter, the background light will average to nearly 0.

If you have multiple targets where your detector will only see one target
(you can't discern one reflector from another otherwise) you need only
offset the PRBS sequence by more than one bit. Because a time-shifted
correlator will have an extreme triangular peak that rises and falls within
2 bit periods, you only need to time shift the single PRBS pattern to avoid
overlap.

If you don't have the ability to generate all the IR sources locally, you
can use different PRBS patterns or do a google search on "gold codes" for
PRBS style patterns that have limited overlap independent of alignment.


.

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