Newsgroups: comp.robotics
Path: brunix!cat.cis.Brown.EDU!agate!darkstar.UCSC.EDU!news.hal.COM!olivea!sgigate.sgi.com!odin!sgi!wdl1!mail!cps233!dombrows
From: dombrows@lds.loral.com (Brian Dombrowski, 5424)
Subject: Re: Underwater Sonar
Message-ID: <1994Jun16.135708.5934@lds.loral.com>
Sender: news@lds.loral.com
Reply-To: dombrows@lds.loral.com
Organization: LORAL Data Systems
References: <1994Jun15.184941.6833@news.csuohio.edu>
Date: Thu, 16 Jun 1994 13:57:08 GMT
Lines: 46

In article 6833@news.csuohio.edu, dpalmer@csuohio.edu (Darryl Palmer) writes:
> 
> 
> Does any know where to get sonar transducers specifically for underwater
> usage, or how to design one using regular transducers inexpensively?
> Or is my best choice is to go to fishing shops and pick up those
> fish finder units and scavenge parts? This is for an underwater robotic
> vehicle that I am attempting to build, and available space is limited.
> 
> 
> Darryl Palmer
> dpalmer@denning.csuohio.edu


I built a home-brewed side-scan sonar a couple of years ago.  To do this
I modified a ZX81 ( don't laugh ) to run programs from EPROM.  I built
an I/O interface for it that had a few bits of latched, digital I/O, and
one serial 8-bit A/D channel.  

I picked up a used 'flasher' type sonar unit ( you know the type with the spinning
wheel that has a neon light on it ) with the transducer from a tackle shop for $20.
The unit was build around the National LM1812 Sonar transceiver chip ( Digi-Key
sells this chip for under $10. )  The LM1812 takes care of all the BS of the acoustic
signal processing.  You just tell the thing to transmit a acoustic pulse, have your
uP start a timer, and wait for the chip to give you digital pulse when it detects
the reflected signal.  At this point your uP uses the elapsed time from the
time it initiated the blip to the time the reflected blip was detected to calculate
the distance of an object.  I had a gear head motor swing the transducer back and
forth over a 180 degree sweep.  The shaft of the motor was connected to a pot
that was connected as a votage divider between Vcc and GND.  This signal was
fed into the A/D and provided the uP with position feedback for the ultrasonic
transducer.  About 2K of Z80 assemble code allowed me to use the ZX81 pixels
( 48 x 64 ) to plot a sweep bottom profile off each side of the boat on a
5 inch, 12V, B&W TV.  I even had 3 different ranges:  25, 50, 100 ft.
Whole thing works really well and fits in a platic milk crate.

However, most my enjoyment came from building it, and debugging it.  Now,
it just sits around collecting dust.  I'd like to redesign it to use
a 68HC11 and have it transmit the data to a palm top over RS-232 for
displaying.

Good Luck

Bd


