Subject:
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Re: sonar (fwd)
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Sat, 23 Nov 1996 20:55:18 GMT
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Original-From:
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Richard Vannoy <richardv@abac.(stopspam)com>
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Viewed:
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1420 times
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> This is true of the POLAROID Ultrasonic Sensor module, but not
> necessarily true of all Ultrasonic Sensor modules. It depends on the
> type of Ultrasonic Transducer the circuit uses. The one I built uses a
> Piezo-Electric transducer available through a number of surplus places,
> and outputs a 9VDC pulse.
My 20 years of navy sonar help me somewhat with active/passive transducers and things in
the kilowatt range... :-) but I'm a rank newbie to most of the sonar talked about
here. Sounds like Piezo would be very cheap. True? I bought two Polaroids (which will
get set up in a test rig next week, but no way can I afford twenty-four Polaroids in a
ring around a robot. I'd like to learn more about Piezo.
> I'm basing this assertion on the
> information I have on the now-defunct LM1812 Ultrasonic Chip, and the
> Texas Instrauments Sonar Module, which appear to use pretty much the
> same setup as the Polaroid unit. I don't have a Polaroid unit and have
> never actually had one in person, so I might be wrong.
I've just read all the docs on Polaroid and I'd say they are very similar.
> Well, I'm NOT a sonar technician, and I suspect I could learn a thing or
> two from you, but I do have complete schematics and a nice write-up on
> how it all works available on my page:
> http://www.vnet.net/wizorg/wizorg.html Its not as sophisticated as the
> Polaroid unit, nor has quite as much range, but it is reliable and best
> of all CHEAP! Feel free to give it a look and let me know if you see
> anything that could be improved, I'd like to know about it.
Thanks. I'll stop by and take a look.
> Ok Richard, now I have a question for you... in my setup I'm currently
> using two small Murata transducers. They're a matched pair, one to
> transmit, the other to receive. I'm currently getting somewhere around
> 10 feet or so but was wondering if I could reliably get more. Here's my
> question: would it be helpful if I "ganged" multiple transmitters and/or
> receivers together to make a "larger" array?
I think you are leading up to a phased array. I've seen it in megabuck systems, but
have no hobbyist/practical experience. The basic idea is to put two or more transducers
in close proximity and pulse them together. As you get farther out, the signals farther
away from dead center start getting out of phase and begin to cancel each other out.
Then with a circular array, you can really get tricky by sending the transmit pulse at
slightly different times to elements around the "center". This makes the phasing at
some direction exactly in phase and with a very narrow beam width. This effect allows
you to "steer" the active pulse very accurately. Submarines and destroyers have long
realized that a strong pulse sent out 360 degrees was far less effective than a
"concentrated" narrow bean. Back in the late '60s, phased array techniques were
classified SECRET. You need a little more processing power, but nowadays, I see no
reason why you couldn't use phased array on any robot.
> What would the diffulties
> in doing that be (in terms of synchronization and so forth) be and would
> it be worth trying out?
The tronics of sending phased signals would be a challenge, and I've not yet seen
anything about it in hobby literature, but I'm sure it is do-able.
> John Whitten
> brat@naxs.com
ooops. Small world! I was just at your place last night and downloaded your stuff on
stepper moter controller, pot sterring control, etc. Thanks a lot!
--
Richard T. Vannoy II richardv@abac.com
PO Box 103 Computer Programmer
La Mesa, CA 91944-0103 College Electronics Instructor
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Message is in Reply To:
 | | Re: sonar (fwd)
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| (...) This is true of the POLAROID Ultrasonic Sensor module, but not necessarily true of all Ultrasonic Sensor modules. It depends on the type of Ultrasonic Transducer the circuit uses. The one I built uses a Piezo-Electric transducer available (...) (28 years ago, 23-Nov-96, to lugnet.robotics.handyboard)
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