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Question about ultrasonic range finder

J

Joe

Jan 1, 1970
0
Hello to the group,

The only experience I have with ultrasonics is that I built a bat
detector a few years ago which took in 40Khz and divided it down to
where I could hear the clicks of some types of bats (mostly the little
brown bats we have around here). Occasionally, I would also hear other
things, like insects, and who knows what else. What I learned was that
it may not be such a good rangefinder when run at just the 40 Khz
frequency.

Now I would like to design an ultrasonic range finder. I was wondering,
since I will be sending out a pulse and waiting for the echo (actually
the micro will be waiting for the echo). If the signal was modulated
with, say a 1Khz square wave (or whatever), on the same idea as the TV
remotes and receivers (say, tsop series receivers) used which have
pretty high noise rejection, should this, in theory, give me more noise
immunity? The receiver would be the standard 40Khz receiver, but then
the signal would have to go thru a bandpass filter to get at the
modulating frequency. No modulation, then the signal is ignored. If the
modulating frequency comes thru, then 'echo received' .Does this make
sense?

Has anyone done this before, or heard of it being done? Any info, links
(within a reasonable number). I did use google and got 19,800 hits, but
only the first few were relevant, and the articles are only available
for sale. As usual, this is a low budget deal for me. Most of the other
links talked about PWM. I think that's different then what I am asking
about here.

Any questions on clarification (if I did not supply enough
information), opinions, experiences, links, or advice are, as always,
appreciated.

TIA,
Joe
 
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