Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!rice!uw-beaver!fluke!strong From: strong@tc.fluke.COM (Norm Strong) Newsgroups: sci.electronics Subject: Re: Can anyone recommend a sensor? Message-ID: <12925@fluke.COM> Date: 1 Dec 89 19:24:00 GMT References: <472202ca.20b6d@apollo.HP.COM> <69060@psuecl.bitnet> Sender: news@tc.fluke.COM Distribution: na Organization: John Fluke Mfg. Co., Inc., Everett, WA Lines: 26 In article <69060@psuecl.bitnet> peg@psuecl.bitnet (PAUL E. GANTER) writes: }> I guess Polaroid sells a "hacker's kit" with the sonar gizmo they use }> on their autofocus cameras, and I think for under $200. But I seem to }> recall reading that the range was more like 12" - dozens of feet, with }> an accuracy of 1" or worse. Does anyone know if that's a fundamental }> limit on the sensor itself, or only the way the electronics were }> designed in the kit? (Be gentle; I'm mostly a software person. I } }Recently my robotics class was discussing distance sensing, and one }of the methods we covered was acoustics (my prof is doing research }on them). One large problem with acoustic transceivers involves the }air they travel through: the speed of sound in air varies quite a bit }with temperature, humidity, barometric pressure, etc. I don't have }quantitative figures on the variation; I will ask my prof. Try playing }with the formula for speed of sound in most physics texts. I see that }speed of sound varies about 10% from 0C to 100C. Add the effects of }humidity and pressure and you are probably much higher. The tempco of sound in air is about +0.18%/deg C at 20 deg. It's easy to temperature compensate an ultrasonic distance measuring circuit to cancel this factor. Changes due to humidity and barometric pressure are slight and can be safely ignored. -- Norm (strong@tc.fluke.com) Brought to you by Super Global Mega Corp .com