🚀 go-pugleaf

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)