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