Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!mcsun!ukc!warwick!esrgf From: esrgf@warwick.ac.uk (Mr M Stevens) Newsgroups: comp.robotics Subject: Re: Wireless Computer Communication Message-ID: <582@clover.warwick.ac.uk> Date: 7 Jun 90 18:29:59 GMT References: <9352@pt.cs.cmu.edu> <$B^$N*%@ads.com> <398@valideast.COM> <35622@sequent.UUCP> <24493@unix.cis.pitt.edu> Distribution: all Organization: Computing Services, Warwick University, UK Lines: 48 In-reply-to: fmgst@unix.cis.pitt.edu's message of 24 May 90 06:19:53 GMT In article <24493@unix.cis.pitt.edu> fmgst@unix.cis.pitt.edu (Filip Gieszczykiewicz) writes: Greetings. What do you people think of using sound waves as a transmission medium. I think that anything below 10 KHz would have problems with background noise (pumps, 60 Hz, etc.) but anything above 40-50 KHz should work just fine. Does anyone see any problems with this? I've thought of using sound waves for robotic applications a few times but so far haven't done too much about it. The main problem with anything <20K is that it going to drive every person/dog/cat in the vecinity crazy. Higher frequencies (ultrasonics) are of course used a great deal for obstacle detection / range finders. We have some very cheap transducers (2.5 UK pounds each) that although not exectly high performance devices do, are quite capable of detecting resonably sized objects up to about 2 meters away. These opperate at 40KHz. The main feature of sound waves at these sorts of frequencies is that they are reasonably directional and rapidly attenuated; which is why they are so useful as obstacle detectors / range finders. I think you need some quite significant power output (compared with the usual transducers) to get any ranges above a few meters. As far as I remember from my physics wave like propogation in air is quite restricted in its frequency range, and the high the freq the more rapid the attenuation. Having said all that I'm still quite keen on using sound waves for all sorts of things. We have a digitising device around that uses a sparc to generate a sound pulse which is timed by two sensors about 50cm apart to give position. These used be quite popular a few years back as low cost digitising tablets; I guess mice etc killed them off. I've also seen it suggest on a TV sience program (tommorows world), that a similar principle could be used on a larger scale. They showed a room with microphones in the corners. Using these a clicking transmitter could be traced in 3D to an accuracy of about 1cm by timing the arival of the pulses. Trouble is I can't remember who was doing this, sounded like a system that would be fun to setup. I guess in many environments the problems of interfering sound sources would be quite significant though. Anyone else got ideas on the use of sound. I get the feeling that like other senses sound has been a little neglected in the rush to show what large amounts of computing power vision requires. -- -- Michael Stevens -- Dept. of Engineering Univerity of Warwick, Coventry, England