[?] Sending 1200 bps data through 30 -50 feet of water.
David Chapman
Hi..
As the subject heading states I'm interested in transmitting short-
duration on/off switching commands through around 50 feet of water (of
both salt and fresh varieties) to a receiving unit.
Having witnessed UHF radio being tried VERY unsuccessfully for this
purpose some years ago, I was now intending to try using an ultrasonic
frequency of around 40KHz since transducers for this frequency are
readily available from a number of sources.
The data rate I was intending to use is only 1200 bps and the commands
only comprise a few data bytes so, if the Hi-Q of these transducers is
likely to cause problems at that data rate it can be reduced, right down
to around 100bps or so if necessary.
Is anyone with any practical experience of communicating through water
willing and able to share some of their knowledge, or maybe recommend
suitable types of transducers that might be suitable for this task?
Is there a better way of 'wire-less' signalling through 50 feet or so
of water? In this application component cost is less important than
performance and reliability.
All (sensible) suggestions and ideas will be gratefully received.
TIA - Dave
David C.Chapman - Chartered Engineer. FIEE. (dcch...@iee.org)
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Win Hill
>
> Hi..
>
> As the subject heading states I'm interested in transmitting short-
> duration on/off switching commands through around 50 feet of water (of
> both salt and fresh varieties) to a receiving unit.
>
Yawn. At the distances and data rates you propose it's comically easy.
Provided you don't have nearby reflecting surfaces, almost any scheme
you try will work fine.
Your biggest issue will be underwater moldings, connectors, etc. Consider
using fish-finder transducer replacement parts, 200kHz is a common frequency.
Whatever, go with what you find mechanically and financially satisfactory.
- Win
Winfield Hill
Rowland Institute for Science
100 Edwin Land Blvd
Cambridge, MA 02142-1297
Richard Harrison
"Is there a better way of signaling through 50 feet or so of water?"
Maybe so.
I`ve experience with underwater ultrasound. It works. My company
installed acoustic (ultrasound) valve locator and control gear on the
seabed. It worked on location and up to 5 miles to find a valve. We
would dunk a transducer from a boat or helicopter and a transponder on
the valve would reply so we could zero in on the site before opening or
closing a valve. We only communicated at 30 baud using BCH coding and
other precautions.
With GPS now available, finding the valve is no longer a challenge.
Our installations were long ago, but at the time Edo Western Corp. had
some off the shelf gear, but we chose Bendix to develop a complete
system for us. Edo`s transducers were deep ocean types which may have
been inappropriate in the Gulf of Mexico.
I`ve also built gear for finding buried pipelibes. I would match an
audio generator to the pipe to ground circuit with a Variac. Pipelines
are nominally insulated from ground for corrosion control. The route of
the pipe could then be found or followed from the amplified output of a
search coil. I started with audio tones but went to 12 hertz for greater
distance on shore. Coating is thin. Capacitance to ground is high. The
steel pipe, though 3 or 4 feet in diameter has considerable resistance,
so attenuation is a function of frequency. Have reached 8 to 10 miles
from the sender down the pipeline.
Found undersea buried pipelines using audio tones at frequencies of 400
to 1200 hertz. Plenty of signal anywhere in the vicinity of the platform
when the sender was connected to the pipe and platform structure. Plenty
of tone when the pickup coil was still in the boat in several hundred
feet of water. Divers with waterproof search coils had no problem
finding and following the pipe route on the bottom. In murky water the
diver tethers himself to the platform so that his stroll will take him
in an arc to find the pipe`s route. Then, he can follow an azimuth.
This pipe finding experience leads me to believe it would be easy to
communicate 50 or more feet using only electrodes at each end of the
circuit if you were able to get some spacing between the electrodes in
each pair, preferably more distance than the distance between sender and
receiver.
Best regards, Richard Harrison, KB5WZI
John Woodgate
inimitably wrote:
>Yawn.
That's an unusual type of remark from you. Moreover, it's somewhat inapt
in the context. Dave is a bit of a whiz at the r.f. stuff, and asking
advice about ultrasonics is probably due to professional caution.
--
Regards, John Woodgate, OOO - Own Opinions Only. Phone +44 (0)1268 747839
Fax +44 (0)1268 777124. http://www.jmwa.demon.co.uk I wanted to make a fully-
automated nuclear-powered trawler,but it went into spontaneous fishing.
PLEASE do not mail copies of newsgroup posts to me.
John Woodgate
<da...@chassis.demon.co.uk> inimitably wrote:
> As the subject heading states I'm interested in transmitting short-
>duration on/off switching commands through around 50 feet of water (of
>both salt and fresh varieties) to a receiving unit.
>
> Having witnessed UHF radio being tried VERY unsuccessfully for this
>purpose some years ago, I was now intending to try using an ultrasonic
>frequency of around 40KHz since transducers for this frequency are
>readily available from a number of sources.
The transducers you need for under water are very different from those
that work in air. Maybe you already knew that, but AIUI, 40 kHz is not
particularly popular for under-water use.
If it's still water, and you don't need to go down to any great depth,
it should work well. If the enclosure has hard vertical walls, though,
you are bound to get a strong interference pattern with nulls.
The speed of sound in water is about 1500 m/s, and the attenuation is
measured in millinepers/m at 50 kHz, much less at lower frequencies.
The Acoustics Group at NPL can give you a lot of help on ultrasonics
under water.
Gerry Schneider
Richard Harrison wrote:
> David Chapman wrote:
> "Is there a better way of signaling through 50 feet or so of water?"
>
> Maybe so.
>
> I`ve experience with underwater ultrasound. It works. (snipped good
> technical stuff).
Yes, I agree that sound is a good method, but thermoclines, snapping shrimp,
boat props and various reflection sources can play havoc at the higher data
rates. We used to do 40 kHz FM (US Navy) and 8 kHz SSB (commercial diver)
voice communications for full face masks and rat hats, but the human ear can
ignore a lot of extraneous junk. Data transmission was something we tried
but didn't have the resources or market to pursue (this was back in the late
'70's).
> (snip) This pipe finding experience leads me to believe it would be easy
> to
> communicate 50 or more feet using only electrodes at each end of the
> circuit if you were able to get some spacing between the electrodes in
> each pair, preferably more distance than the distance between sender and
> receiver.
We tried that, and found that at a separation of about 3 times the electrode
spacing was a practical limit, based on the available power level. The
signal level went down *fast* after about 1.5 times spacing. As you say,
it's a fairly simple method.
Gerry
Kevin Aylward
news:GoUU8GCw...@jmwa.demon.co.uk...
I would suggest one thing here though. If you do happen to go off on a small
boat, just of the Portsmouth coast for example, in order to test the
functioning of any marine telemetry equipment that you might be involved in
the design of. It is to insure that you have taken the appropriate pills
that one might deem appropriate for journeys such as these, on the open sea.
Unfortunately, in my own case, I was not so enlightened at that point in
time, and as such, after having my morning breakfast vacate my stomach in
the most unusual manner, resolved never to take such careless action in the
immediate future.
Kevin Aylward , Warden of the Kings Ale
ke...@anasoft.co.uk
http://www.anasoft.co.uk - SuperSpice "Cheap, No Shit!", a currently free
GUI xspice, unlimited component, mixed-mode Windows simulator with Schematic
Capture, waveform display, FFT's and Filter Design.
Opinions of my employer are not necessarily indicative of my own
Oscillators don't, amplifiers do"
Tim Hubberstey
>
> I would suggest one thing here though. If you do happen to go off on a small
> boat, just of the Portsmouth coast for example, in order to test the
> functioning of any marine telemetry equipment that you might be involved in
> the design of. It is to insure that you have taken the appropriate pills
> that one might deem appropriate for journeys such as these, on the open sea.
> Unfortunately, in my own case, I was not so enlightened at that point in
> time, and as such, after having my morning breakfast vacate my stomach in
> the most unusual manner, resolved never to take such careless action in the
> immediate future.
>
> Kevin Aylward , Warden of the Kings Ale
Is there any possibility that consumption of the "Kings Ale" had
anything to do with your misplacing of your stomach contents? ;-)
--
Tim Hubberstey, P.Eng. . . . . . . . . . . . . . . Marmot Engineering
Vancouver, BC, Canada . . . . . Hardware/Software Consulting Engineer
Win Hill
>
> David Chapman wrote:
>>
>> As the subject heading states I'm interested in transmitting short-
>> duration on/off switching commands through around 50 feet of water (of
>> both salt and fresh varieties) to a receiving unit.
>>
>> The data rate I was intending to use is only 1200 bps and the commands
>> only comprise a few data bytes so ...
>
> Yawn. At the distances and data rates you propose it's comically easy.
> Provided you don't have nearby reflecting surfaces, almost any scheme
> you try will work fine.
>
> Your biggest issue will be underwater moldings, connectors, etc. Consider
> using fish-finder transducer replacement parts, 200kHz is a common frequency.
> Whatever, go with what you find mechanically and financially satisfactory.
I'm sorry for my somewhat flippant answer this morning, that was totally
uncalled for. Actually my remarks were right on target however. Sound
transmission in water is exceptionally efficient, 5x faster than air and
with relatively low absorption and with very good coupling to transducers.
If you have a straight shot to a target it's very easy to send almost any
kind of signal, even "speech or music" etc. You can use almost any type
of ac data modulation scheme (but no required dc signal transmission).
However, if there are scattering surfaces or multiple reflectors (the water
surface is a reflector) etc, the issue becomes more complex for higher data
rates. (The idea of a slow data rate is to let all the multipaths die out
for each data symbol before sending the next one.) Under the common but
adverse circumstance of multipath, using higher data rates will require some
type of frequency-diversity technique. For example, I wrote a detailed paper
on a chirp technique that's simple and easy to implement (copies on request).
Perhaps if you describe your application in a bit more detail I can make
further suggestions.
Thanks,
Kevin Aylward
news:39B848E2...@mediaone.net...
Actually, now that we are talking ultrasound, I do have another really nifty
Windows GUI program that you can have a copy of (Win, John, Jim, or anyone
else). It's one I wrote for medical imaging. It takes an input of transducer
characteristics, such as pitch, number of elements and frequency etc, in
addition to focal point positions etc... etc.. and calculates and displays
quite nicely, if I say so myself, various things such as the required delays
and the actual tapping point locations for analog delay line implementations
of ultrasound beamformers. It actually produces the final code that is blown
into the prom for the product it was wrote for, but this data won't be of
much use to you all. Nevertheless it does solve some tricky bits of
trigonometry, as curved arrays and annular are supported as well.
Let me know if there is any interest I will post it on my site
Kevin Aylward , Warden of the Kings Ale
Spehro Pefhany
> Actually, now that we are talking ultrasound, I do have another really nifty
> Windows GUI program that you can have a copy of (Win, John, Jim, or anyone
> else). It's one I wrote for medical imaging.
I'd be interested in having a peek at this, Kevin.
Oh, and BTW, for your tag-line, perhaps tacking an "e" on the end of the
offending word might be enough? That softens it to my ears, not sure how
it sounds to a Brit.
Best regards,
--
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Spehro Pefhany --"it's the network..." "The Journey is the reward"
sp...@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
Contributions invited->The AVR-gcc FAQ is at: http://www.BlueCollarLinux.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Jan Panteltje
>
>> Actually, now that we are talking ultrasound, I do have another really nifty
>> Windows GUI program that you can have a copy of (Win, John, Jim, or anyone
>> else). It's one I wrote for medical imaging.
what input does the program want, a moving transducer?
Jan
Kevin Aylward
"Jan Panteltje" <j...@panteltje.demon.nl> wrote in message
news:968410170.15156....@news.demon.nl...
It calculates and displays, in convenient form, the data required to make an
analog beamformer. In short, ultrasound transducers have lots of elements,
you pulse a subset of these elements in the required phases in order to
focus at each distant point. The number of elements you use sets the
beamwidth. Lookup "phased array". Linear and convex arrays need different
delays. My program calculates it all from simple specs.
Spehro Pefhany
> But what exactly does it do? i did some experiments with ultrasound doppler,
> what input does the program want, a moving transducer?
> Jan
That's the "old" way to do sonography, modern transducers are phased
arrays as Kevin explains.
Kevin Aylward
I will try and post the software over the weekend. I have to get all the
files together in one zip and although it does have some help, it needs a
basic description of what GUI design forms are required to be setup. I also
list all the equations used in the help. It actually can output the required
data for a full digital beamformer as well!
Kevin
"Spehro Pefhany" <sp...@interlog.com> wrote in message
news:Mo4u5.14995$E_6.4...@news3.rdc1.on.home.com...
John Woodgate
<kevinan...@home.com> inimitably wrote:
>It is to insure that you have taken the appropriate pills
>that one might deem appropriate for journeys such as these, on the open sea.
>Unfortunately, in my own case, I was not so enlightened at that point in
>time, and as such, after having my morning breakfast vacate my stomach in
>the most unusual manner, resolved never to take such careless action in the
>immediate future.
I understand that the main problem with sea-sickness is that you feel
you might die any minute, and fear that you won't. (;-)
--
Regards, John Woodgate, OOO - Own Opinions Only. Phone +44 (0)1268 747839
Fax +44 (0)1268 777124. http://www.jmwa.demon.co.uk I wanted to make a fully-
Lizard Blizzard
> David Chapman wrote:
> > Hi..
> > As the subject heading states I'm interested in transmitting short-
> > duration on/off switching commands through around 50 feet of water (of
> > both salt and fresh varieties) to a receiving unit.
> > The data rate I was intending to use is only 1200 bps and the commands
> > only comprise a few data bytes so ...
> Yawn. At the distances and data rates you propose it's comically easy.
> Provided you don't have nearby reflecting surfaces, almost any scheme
> you try will work fine.
> Your biggest issue will be underwater moldings, connectors, etc. Consider
> using fish-finder transducer replacement parts, 200kHz is a common frequency.
> Whatever, go with what you find mechanically and financially satisfactory.
So this implies using an ultrasonic carrier modulated with the data? It
doesn't say so explicitly. At first I was thinking that it would be
over a light beam because RF is 'not practical'. I was thinking more
towards the blue end of the spectrum.
ed....@att.net
sorry to attach to the thread at the middle
David,
take a look at www.benthos.com
they have a nice tutorial, and application page for their Telesonar
Acoustic Modem .. they claim a throughput rate of close to 2400 b/s,
without use of any error reduction technique but of course state that
nothing is concrete in terms of distance ... .. is the transducer
omnidirectional or directional ... salinity, temperature, etc but
your needs should be easily met ... or at least hints as to how you
can meet them yourself (?). Price might be prohibitive.
The modem came from Datasonics
if you are looking at on/off commands, there are subsea solutions
already out there in the transponder/interrogeter configurations you
can use for ideas
- Ed
Jan Panteltje
Read 1209 postings on DTV today... (yes technical)
Jan
Jan Panteltje
Jan
Winfield Hill
>
> Win Hill wrote:
>
>> David Chapman wrote:
>
>>> The data rate I was intending to use is only 1200 bps and the
>>> commands only comprise a few data bytes so ...
>
>> Provided you don't have nearby reflecting surfaces, almost any
>> scheme you try will work fine.
>
>> Your biggest issue will be underwater moldings, connectors, etc.
>> Consider using fish-finder transducer replacement parts, 200kHz is
>> a common frequency. Whatever, go with what you find mechanically
>> and financially satisfactory.
>
> So this implies using an ultrasonic carrier modulated with the data?
> It doesn't say so explicitly. At first I was thinking that it would
> be over a light beam because RF is 'not practical'. I was thinking
> more towards the blue end of the spectrum.
Light is not so practical in the ocean because of frequent events
of limited visibility, such as after storms.
Modulated sound on the other hand is easy and inexpensive to use.
Thanks,
Kevin Aylward
> >
> >"Jan Panteltje" <j...@panteltje.demon.nl> wrote in message
> >news:968410170.15156....@news.demon.nl...
> >> >In sci.electronics.design Kevin Aylward <kevinan...@home.com>
wrote:
> >> >
> >> >> Actually, now that we are talking ultrasound, I do have another
really
> >nifty
> >> >> Windows GUI program that you can have a copy of (Win, John, Jim, or
> >anyone
> >> >> else). It's one I wrote for medical imaging.
> >> But what exactly does it do? i did some experiments with ultrasound
> >doppler,
> >> what input does the program want, a moving transducer?
> >> Jan
> >
> >It calculates and displays, in convenient form, the data required to make
an
> >analog beamformer. In short, ultrasound transducers have lots of
elements,
> >you pulse a subset of these elements in the required phases in order to
> >focus at each distant point. The number of elements you use sets the
> >beamwidth. Lookup "phased array". Linear and convex arrays need different
> >delays. My program calculates it all from simple specs.
> >
> Thanks, facinating. I would love to see the math :-)
> Jan
I have most of the equations in the help file, so hopefully I can get it all
together over the weekend, in between making more transformers for
SuperSpice.
David Chapman
Many thanks to all those who took the time to reply and offer
interesting/useful suggestions in response to my original posting.
I have just one further question, if I may...
Can anyone recommend a source of smallish, modestly priced underwater
transducers that operate in the 200KHz region?
I'm not looking for military grade transducers at military grade
prices.
The system I want to produce will comprise a small portable
transmitter/transducer that can be lowered a few inches into the water
from a small boat, and a small transducer/receiver package that can be
sunk, for a few days at a time, in inshore waters, and never at depths
greater than 50-60 feet.
Data will only ever be sent from the surface to the sunken receiver -
no return acknowledgement will be required.
Any suggestions on suitable small transducers for this application,
preferably ones that are easily obtainable in the U.K?
Many thanks - Dave
ed....@att.net
David ...
Some of these firms are the base providers and probably won't be
financially viable for a one-off ... BUT they might be able to point
you in the right direction or give more ideas from their web sites.
200kHz tranducers are available in a wide range of fish finders which
start at $99 U.S. for the whole thing (Hummingbird 100SX for instance
which is probably about a 20 degree beam). Add-on transducers seem to
be the same with or without the fish finder :^)
more info sources :
Airmar U.S. http://www.airmar.com/
Airmar is the mfg I think of ... and while they have a light marine
section, it's for mfg's ... though their site has info that might let
you select the proper transducer and then buy a transducer from a
fishing supply house (replacement, add-on or parts from a dead unit ?)
Transonics U.S. http://www.sisna.com/transonics
MSI U.S. http://www.matsysinc.com
MSI U.K. http://www.oct-ltd.co.uk
LinkQuest U.S. http://www.link-quest.com/
acoustic modems for UW use .. has a decent FAQ and tech notes which
might be of help (worth a look).
AppliedAcoustic U.K. http://www.appliedacoustics.com
has an acoustic modem
- Ed
Richard Harrison
"I would suggest one thing here though, if you do happen to go off in a
small boat---."
Reminds me of our first tests. The U.S. Navy was notified in advance of
our ultrasound tests at sea. Somebody didn`t get the word, or the Navy
was taking no chances that we were cover for some other operation.
Several magnetometer planes appeared overhead and a small floatilla of
warships approached at flank speed. We could have been blown out of the
water had anyone lost his cool. It`s reassuring that someone was
vigilant in those times of a cold war.
John Woodgate
<da...@chassis.demon.co.uk> inimitably wrote:
> Can anyone recommend a source of smallish, modestly priced underwater
>transducers that operate in the 200KHz region?
Win Hill suggested fish-finder equipment. It seems the most promising.
--
Regards, John Woodgate, OOO - Own Opinions Only. Phone +44 (0)1268 747839
Fax +44 (0)1268 777124. http://www.jmwa.demon.co.uk I wanted to make a fully-
automated nuclear-powered trawler,but it went into spontaneous fishing.
klock...@cix.compulink.co.uk
Woodgate) wrote:
> Win Hill suggested fish-finder equipment. It seems the most promising.
But don't expect any technical help - I once tried to get some technical
info of Lowrance so I could use one of their echo sounders for a special
project. They stone-walled and wouldn't even give me as much info as
their repair men get.
Try and find a local repair shop that handles echo sounders and see if
they will let you look at the maintenance manuals - the transducer driver
and receive circuits will be helpful.
Win Hill
Have things changed in the last 5 years? While waiting for a tire to be
balanced 5 years ago, I went next door to the Marine superstore. They had
perhaps two dozen depth-finder models on sale. About half of the them had
the operator's manual out for viewing, and half of these included schematics
in the back. Has this apparent industry practise now changed?
Anyway, as far as David Chapman's application is concerned, he'd not likely
to find the fish-finder circuits very useful, because he's transmitting data
and is going a much shorter distance. However the fish-finder transducer is
a handy starting point. Naturally he'd have to characterize the transducer
(e.g. measure its capacitance) before designing a circuit to drive it. It's
useful to simplify the driving of piezoelectric transducers with a series
inductance resonant at the driving frequency, which frequency should in turn
be selected to match any acoustic resonance of the transducer, which would
likely be at the advertised operating frequency of the fish finder. Drive
the inductor-transducer with a voltage source, say a FET gate-driver chip.
Return the transducer to ground through two reverse-wired parallel diodes,
providing a received-signal pickoff point.
Thanks,
- Win
Winfield Hill
Rowland Institute for Science
100 Edwin Land Blvd
Cambridge, MA 02142-1297
Kevin Aylward
Small point here. Transmitting at the resonant frequency of the transducer
system is not necessarily the best way to go. In medical imaging, and in the
telemetry stuff I have been involved with, you transmit off resonance. This
is to increase the bandwidth for better date rates, and reduce ringing in
order to obtain finer imaging resolution. In fact with, medical imaging you
are trying to get only one (or 1/2 even) cycle (x=v/f)!.
Win Hill
>
> test
I think your test message made it more than
50 feet, although it wasn't through water!
klock...@cix.compulink.co.uk
wrote:
> klock...@cix.compulink.co.uk wrote:
> >
> > j...@jmwa.demon.co.uk (John Woodgate) wrote:
> >
> >> Win Hill suggested fish-finder equipment. It seems the most
> > promising.
> >
> > But don't expect any technical help - I once tried to get some
> > technical
> > info of Lowrance so I could use one of their echo sounders for a
> > special
> > project. They stone-walled and wouldn't even give me as much info as
> > their repair men get.
> >
> > Try and find a local repair shop that handles echo sounders and see if
> > they will let you look at the maintenance manuals - the transducer
> > driver
> > and receive circuits will be helpful.
>
> Have things changed in the last 5 years? While waiting for a tire
> to be balanced 5 years ago, I went next door to the Marine superstore.
> They had perhaps two dozen depth-finder models on sale. About half
> of the them had the operator's manual out for viewing, and half of
> these included schematics in the back. Has this apparent industry
> practise now changed?
Seems so. With the blessing of their European Sales Manager, I emailed
and faxed their HQ about 10 times in all and was either not answered or
told that their technical department was looking at the problem. Not a
good advert for the company.
Keith.