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> data carried by the 60 kHz light pulses.  It can be advantageous
> to include some high-pass filtration in the receiver, to remove those
> higher frequency harmonics, but that isn't touch and not always
> needed, especially if you are just after a "present/absent" detection.

Oops.  I meant low-pass filtration.

I attached a block diagram gif of the system, a very simple one.

Mike H.

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