Re: infrared wall to detect an object
- From: Oliver Betz <OBetz@xxxxxxxxxxxxx>
- Date: Sat, 13 Jan 2007 18:25:43 +0100
David R Brooks wrote:
[...]
Use any waveform you want to modulate the sender, and use that same
waveform to demodulate the received signal - essentially multiply the
two together, but as analog signals. Then low-pass filter the result, &
digitise. Mathematically, you are correlating the two signals.
For added security, use a pseudo-random source (ie shift register) for
the modulating signal - it's *most* unlikely some external interference
will mimic that.
TANSTAAFL - if you want some speed, you need some bandwidth, and then
you will detect also noise "not having the same waveform".
But at least you spread the spectrum by using the PN-sequence.
There are also other sequences with suitable properties. Finding the
right one is "interesting", but depending on the application, the
improvement might be small.
Oliver
--
Oliver Betz, Muenchen (oliverbetz.de)
.
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