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From: commgrp@silver.UUCP
Newsgroups: sci.electronics
Subject: Re: Ultrasonic Distance Measurement
Message-ID: <24300005@silver>
Date: Sat, 14-Mar-87 12:24:00 EST
Article-I.D.: silver.24300005
Posted: Sat Mar 14 12:24:00 1987
Date-Received: Sun, 15-Mar-87 04:52:29 EST
References: <8455@aero.ARPA>
Organization: Indiana University BACS, Bloomington
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Nf-From: silver.bacs.indiana.edu!commgrp    Mar 14 12:24:00 1987





Re: Ultrasonic Rangefinders

Simple sonic/ultrasonic rangefinder-- Requires two units, transmitter
and receiver:

Transmitter simultaneously emits flash of light and pulse of sound.
Reciever starts timer when it detects light, stops timer when sound
arrives.  Time is proportional to distance between transmitter and
receiver.  Since the first sound to reach the receiver will be that
which has travelled in a straight line between them, there will be no
problem with echoes.

Sound travels ~1100 feet per second, or about an inch in 1/10 ms.  The
wavelength of sound should be a fraction of the unit's resolution; about
40 kHz should be suitable for a unit which indicates the nearest inch.

-- from "How to make an ultrasonic rangefinder" by Bill Mixon, reprinted
in SPELEONICS 4 (v.1 no.4 winter-spring 1985-86)

---

Frank Reid
reid@gold.bacs.indiana.edu