Propeller & underwater sonar/depth finder?

abreuma

I've been searchning for previous work or examples of using a microprocessor to take depth measurements of a small body of water using either a hacked depth/fish finder or one of these:

http://www.hobbyengineering.com/H2210.html

I haven't had much luck.

What's not clear to me is whether a microprocessor has the raw horsepower to do the timing measurements required or not.· I'm posting here because the Propeller seems to be a pretty powerful micro so there may be a chance that it can do the raw timing.

If anyone has any pointers to examples of how this could be done, or some opinion on whether a Propeller can do this or not, I'd love to hear from you.

(I'm new to microprocessors and an IT geek with an idea.· Comfortable with PLCs but not really a EE type.)

localroger

Doing the timing will be no problem -- the Prop can accurately measure time intervals to better than 1 microsecond accuracy, and better than 0.1 microsecond if you creatively use the counter/timers. The main thing is the interface between the Prop and the transducer.

VIRAND

A few years ago I was interested in Bathymetry (?) of bodies of water,
such as to use sonar to image the topography (depth, bottom surface)
of them. As GPS was not available enough then, I designed a VOR which
I was not aware of as being already invented so I called it a LPS (local
position system). The VOR sends 3 different signals which simply give
polar coordinates; an omnidirectional IR sync pulse, a different IR angular beacon, and
an aerial sound pulse sent at the same time as sync to provide radius
(distance from VOR/LPS "lighthouse" beacon). I believe I released this
previously but if so, again, as a public domain invention. GPS may be
a better option now.

Once having the coordinates, I figured on pinging the bottom with small
piezo. Also, I thought it would be curious to photograph (scan to make an image) using sonar.
The aerial speed of sound is approximately 1100 feet per second, and the
aquarial speed is about 5 times greater I think, one mile per second or
more.

I only got as far as ... testing my pinger in the air with an oscilloscope.
The return pulse was very noisy but showed definite amplitude corresponding
to the distance of a solid object. ... And making a sonar card for a 80286
laptop which may have used a PIC16c54 to measure distance, and also may
have attempted to use 3 small piezos and/or DIY condenser microphones
but the data returned could not be recognized for triangulation,
according to my knowledge at that time.

Summary: I believe the Propeller is capable of sonar imaging according to its
speed (surely in PASM). The resolution depends on wavelength, the inverse of
frequency, and my research suggests optimum aquarial resolution at 3.5 MHz
(but not what type of transducer is capable). 3.5MHz seems optimal for prenatal
sonogram as 4 MHz seems to be less penetrating. For use on boats, the frequencies
between 73 and 450 KHz have different qualities with the lower frequency propagating
further with less detail. 450 KHz may be more useful for fish finders but I do not
recall; 150 KHz is used for visualizing the bottom surface I think.

My preferred method, released to public domain, is to have a modified RC toy boat,
automatically using GPS coordinates to plot a bitmap or 3D topograph of a body of water,
according to sonar data (ping return time), and the boat be programmed to explore
for unplotted coordinates and then return home upon covering an area or upon
receiving an RC signal. It should be considered that the pings are click-like according
to my proposed design, and that the ping-clicks may attract fish (which may or may not be
a desirable effect, as they may make a noisy map). The ping signal would be a minimum number
of cycles at the chosen frequency, although a single pulse at the highest frequency would
provide the best results if it could be recognized as a return signal, because the fourier
transform of a pulse shows it contains all lower frequencies down to the inter-ping period,
which should be longer than the maximum usable ping-return period to avoid artifacts
from old pings (ghost images).

I have not produced any sonograms and that project has been on the shelf since
the early 2000 decade, labeled "to finish someday".

Regarding ultrasound, I have had apparently better results using tiny piezos and microphones
than with specific "ultrasonic transducers" like the ones on the Ping product, but the ones I had no
success with may have been manufacturer rejects sold as surplus, since they had no detectable
input or output. Also, tiny electret mics may be excellent for aerial sonar experiments, but keep
in mind that water quickly destroys them, probably because they are electrostatically charged
insulators. Salt water is very harsh on electronics, and may initiate corrosion that will destroy
a DIY sonar soon after its first use is completed. It may help to coat the piezos with polyurethane
or acrylic to prevent chemical reactions with salt. The piezos and microphones should be tiny
for any hope of usefulness above 50 KHz because the resolution depends both on the wavelength
and the size of the transducers... too big means large blurred-together pixels, and less efficiency
at higher frequencies.

Pinholes make universal high resolution lenses and may permit larger and more powerful and
sensitive transducers, and opportunity to keep them dry, but pinholes are also inefficient lenses
with no signal gain. Zone plates are advanced pinholes, which I have not yet tried, which may
have the gain necessary to diffract light in a high-gain way similar to a magnifying glass under the sun.
Being "universal", they can also focus sound and other energy. I have not tested zone plates for
such gain, but they are closely related to fresnel lenses.

The knowledge I dispensed is according to my experience and may not be recognized by any
peer-reviewed or conventional techniques.

Edit:to add... moderate to high gain analog amplifiers will be necessary in the systems I described,
depending on the application range. LM386 types or low voltage op-amps may be sufficient.

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I should be typing in Spin now.

Post Edited (VIRAND) : 2/7/2010 10:01:37 PM GMT