Newsgroups: comp.robotics
Path: brunix!uunet!zaphod.mps.ohio-state.edu!sol.ctr.columbia.edu!The-Star.honeywell.com!umn.edu!csus.edu!netcom.com!nagle
From: nagle@netcom.com (John Nagle)
Subject: Re: Sonar and the 68HC11
Message-ID: <1993Jan24.031605.26279@netcom.com>
Organization: Netcom - Online Communication Services  (408 241-9760 guest) 
References: <EfM5_Ya00WBM458UUW@andrew.cmu.edu>
Date: Sun, 24 Jan 1993 03:16:05 GMT
Lines: 33

James Ryan Miller <jmce+@andrew.cmu.edu> writes:
>    I am curious if anyone has programmed a 6811 to find distances with
>one of those polaroid sonar things.  
>    Here is how I'm envisioning it ... The 6811 could pulse a trigger
>line which has the transducer xmit a "ping".  When the ping was
>received, it would pulse a line that the 6811 would time, and calculate
>distance.  With the great Input Capture features of the 6811, the
>software should be easy, but how much circuitry is needed to have these
>two nice digital lines at the computer to actually driving the
>transducer.

       All you need is a Texas Instruments type SN28827 Sonar Ranging
Module, which is a board about 1.5" square.  The application note
(D2780, October 1983) explains how to use it.  Runs on +5, but you need
a big external capacitor for filtering, because it draws about an amp
for a few milliseconds when it "pings".  This unit drives the round,
electrostatic Polaroid transducer.  There's a similar unit for the
rectangular pizeoelectric transducer.

       Control is simple; you raise INIT, and it pings; when you get
an echo, the board returns ECHO.  INIT and ECHO can be connected
directly to the appropriate pins of a 68HC11.  Works fine.

       I did this back in 1987, and you may have trouble finding the
modules.  But contact TI headquarters in Dallas, and bug them until
they tell you how to order.  Price runs around $30-50 each.  TI built
some vast number of these things for some camera application, and they're
still around.  I've seen them in a surplus catalog, but don't have the
reference.

       I have FORTH code to drive these things, if anyone needs it.

					John Nagle
