From: Richard Dungan
Subject: Re: Any info about depth sounders?
Date: Mon, 09 Dec 2002 19:47:54 +0000
Organization: Radix Electronic Designs
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NNTP-Posting-Date: Mon, 09 Dec 2002 19:43:02 +0000
>Can anybody give any advice, or preferably a schematic for a depth sounder
>for a boat?
>I want to design a combined speed/distance log and depth sounder using sound
>waves through the water, but this is an area that I haven't been into
>before. I can get ultrasonic transducers from Maplin, but I don't even know
>if ultrasonic is the best frequency to use. All those old films of people
>sweating in submarines while the destroyer above tries to sound them out,
>used an audible 'ping'. Is that a more trasmissive frequency to use in sea
>water, or was it just that ultrasonics wasn't really available during the
>last world war? When I find the best frequency to use, how many cycles
>should in build into the ping? An echo from a hard bottom probably isn't too
>difficult, but if the botton is soft mud?
Most commercial echo sounders use frequencies from the high tens to the
low hundreds of kilohertz. The lower frequencies give you more range at
the expense of resolution.
I suspect that a lot of the WW2 kit operated at low frequency because
the technology could not cope with anything higher, and also because if
it remains audible, some of the processing can be delegated to the human
>The other thing is - the ultrasonic transducers from Maplin normally work in
>air. What is the best way to couple the sound to the water - by having an
>air gap in front of the transducer, or by potting the transducer in a tube
>full of waterproof potting compound which dips into the water?
You might be better off getting a replacement transducer for a marine
sounder. Furuno come to mind, but there are many others. I think that
the modifications would kill your Maplin air sounders.
At one time NatSemi made a chip for basic echo sounder applications, the
LM1812. Please email me privately, avoiding the spam trap, if you cannot
find a data sheet and applications.
So far as your log is concerned, you can extract the speed over the
bottom by measuring the doppler shift of the received echoes. There is a
great deal more to it at the serious end of the market, but that should
not worry you.
Radix Electronic Designs, Orpington, UK