Newsgroups: comp.robotics
Path: brunix!sgiblab!spool.mu.edu!howland.reston.ans.net!pipex!uunet!utcsri!psych.toronto.edu!colin
From: colin@psych.toronto.edu (Colin Hinz)
Subject: Re: Polariod sonar blanking dilemma 
Message-ID: <CF588E.M10@psych.toronto.edu>
Organization: Department of Psychology, University of Toronto
References: <1993Oct18.214610.20660@ncsu.edu>
Date: Tue, 19 Oct 1993 12:05:02 GMT
Lines: 29

In article <1993Oct18.214610.20660@ncsu.edu> rmlegran@eos.ncsu.edu (RICHARD MARK LEGRAND) writes:
>I am using the infamous Polaroid sonar modules on an autonomous vehicle,
>and I am having problems with sensing obstacles less than a foot or
>so away from the transducer.
>
>I'm pretty sure this is because of the internal blanking that the module
>performs to prevent detecting the transducer ring.  The real problem
>seems to be that closer objects (closer than 1.3 feet) lie within this
>blanking period and instead of the first echo being received, the second or
>third echo is received giving the illusion that there is as much as two
>or three times the actual distance to the nearest object.
>
>Is there a way to improve the module's performance by having it indicate that
>objects less than 1.3 feet away are simply 1.3 feet away instead of 2 or 3
>feet away (for example)?  Has anyone dealt with this problem and had any
>success?
>
I could be talking through my hat here, but don't the modules presently
use the T.I. TL851/852 chipset? In that case, it's very simple: the BINH
input is used to control the length of the blanking interval. When
bringing INIT high to start the firing cycle, BINH must be low. Bring
BINH high at the start of the measurement interval. An approximation of
reality is the speed of sound in air is 1 centimeter in 58 microseconds.

Hope this is useful.

- Colin (colin@psych.toronto.edu)


