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Topic: Low-frequency radio modules for under water communication (Read 509 times) previous topic - next topic

DaveEvans

...excite the piezo devices with a carrier, and then do a little frequency modulation on the carrier wave...
or just do OOK?

windoze_killa

@ OP.

What sort of communications do you want to achieve?
Engineers design things.....technicians make them work.

I don't need anti-static wrist straps.....an instructor years ago told me I had no potential.

DaveEvans

In typical trickle fashion, this was revealed in OP's post 8:

Quote
...send some sensor values with a few bytes...
Currently unspecified:

Sending from underwater sensor to above water receiver?
Sending from underwater sensor to underwater receiver?
Sending from above water sensor to underwater receiver?
One-way communication?  Two-way?

Also left unsaid:

The Big Picture, the environment (swimming pool?  lake?), fixed or random orientation between sender and receiver, why wired won't work, whether other technology (besides RF) could be entertained, such as traditional sonar, the piezo idea, blue-green laser, etc.

windoze_killa

I was going to suggest ultrasonics. Flog a few off a wrecked car, in water they should work well.
Engineers design things.....technicians make them work.

I don't need anti-static wrist straps.....an instructor years ago told me I had no potential.

DaveEvans

Quote
I was going to suggest ultrasonics. Flog a few off a wrecked car, in water they should work well.
The commonly accepted wisdom around here is that ultrasonics designed for use in air function poorly, if at all, when submerged because of the vastly higher acoustic impedance presented by water.  Different frequencies and higher power are said to be needed.

However, a group of (college students?) reported limited water depth ranging success with a relatively inexpensive (and crudely waterproofed) Maxbotix product intended for in-air use.  See the Coconut Pi link here: https://www.maxbotix.com/Tutorials/underwater-ranging.htm    A model submariner also reported underwater ranging success with a Maxbotix product - up to 50 feet IIRC.   See that Maxbotix URL for some of the challenges (note it mentions the acoustic impedance issue).

Also, @wvmarle has reported that another inexpensive product intended to be attached to the outside of a tank (for measuring the height of fluid in the tank) can be used to measure water depth if the business end is submerged slightly below the surface.  See posts 21 and 44:  https://forum.arduino.cc/index.php?topic=528653.15

Perhaps either of those sensors could be hacked for the OP's purpose.  But maybe they don't have the necessary range.  A fish finder-type sonar may...   But echos may be a problem.


jremington

Underwater acoustic modems have been available for some time.

This omnidirectional model is capable of 64 bits per second, 200 m range and costs $2000. You will need two, of course.

windoze_killa

I have seen some projects using parking sensors from cars used underwater. As they are sealed and sometimes operate with water or mud on them (obviously reduce effectiveness) they have provided reasonable performance underwater.
Engineers design things.....technicians make them work.

I don't need anti-static wrist straps.....an instructor years ago told me I had no potential.

DaveEvans

I have seen some projects using parking sensors from cars.....reasonable performance underwater.
Interesting.  Got any links?

(Thread has slightly derailed, but the OP seems to be AWOL and the problem and goals are still ill-defined, so...oh well...maybe this will help.)

windoze_killa

I will see if I can find them again. It was a while ago.
Engineers design things.....technicians make them work.

I don't need anti-static wrist straps.....an instructor years ago told me I had no potential.

mbobinger

Thank you guys for your contributions,
I'm based in Germany, sorry for mixing up the frequencies, for me everything below UHF is considered as low-frequency as I play around with LoRa a lot.

For under water transmission, sound or ultrasound might be a good idea but I'l need some out of the box ideas for that since there are no off-the-shel modules for that I guess.

Anyways, your contributions are helpful.

dave-in-nj

you will not be able to use air based things for under water.

you can mount a relay on the side of the pressure hull and activate it like Morse Code.
you would need to be able to listen to the tapping in the other device.

look at the old telegraph key.  instead of an anvil. mount it so it hits the pressure hull.

as a note:  lots of research and probably links to sensors by searching for dolphins.

"The frequency of the sounds produced by a bottlenose dolphin ranges from 0.2 to 150 kHz. The lower frequency vocalizations (about 0.2 to 50 kHz) are likely used in social communication. Social signals have their most energy at frequencies less than 40 kHz. Higher frequency clicks (40 to 150 kHz) are primarily used for echolocation."

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