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Author Topic: IR Receiver Underwater?  (Read 2000 times)
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I'm thinking of make a submarine using an 38kHz IR receiver on the outside of its hull.  Do you think it can read in frequencies underwater sent from my Universal Sony Remote above water?  I was thinking to go this route before attempting bluetooth or WIFI communication just to see how cheap of a solution can work and how well. smiley-cool
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I'm thinking you should "take one for the team" and test that in the bathtub and let us know!

Fascinating stuff on this site  smiley-cool
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What sort of distance through the water are you hope to achieve? IR transmits underwater even less well than visible light.
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My gut feeling is that it would not work.

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I was thinking to go this route before attempting bluetooth or WIFI communication
However you stand a better chance with IR than with radio.
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Hofstadter's Law: It always takes longer than you expect, even when you take into account Hofstadter's Law.
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You would be better off using visible light, see http://upload.wikimedia.org/wikipedia/commons/thumb/1/18/Absorption_spectrum_of_liquid_water.png/350px-Absorption_spectrum_of_liquid_water.png. Underwater ultrasonic transducers would be better, although they are not cheap.
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I'd like to achieve 4.5 foot depth underwater.  I thought a BT module or WIFI board would work fine sealed in a submarine.  Radio communication reflects off water? Also, what if I heat shrink-wrap an ultrasonic ping sensor, mount it on top the hull and use it for obstacle avoidance?  Will the chirp and echo work underwater?

https://www.youtube.com/watch?v=dpRZSziSdSk
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I'd like to achieve 4.5 foot depth underwater.

Are your sender and receiver going to be directly on top of each other, or do you also have a horizontal distance to consider?
« Last Edit: January 18, 2013, 08:54:24 pm by PeterH » Logged

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I thought a BT module or WIFI board would work fine sealed in a submarine.
No they would not.

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Radio communication reflects off water?
No the water changes the wavelength of EM waves. It makes them longer, that means the antenna are no longer tuned up correctly. Plus the fact that water absorbs the radio waves. Submarines have to trail very lone wires, in the order of a few miles to compensate for the change when receiving signals with only a Km or so wavelength. With UHF you have no chance.
Try it and see. 
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I'd like to achieve 4.5 foot depth underwater.  I thought a BT module or WIFI board would work fine sealed in a submarine.  Radio communication reflects off water? Also, what if I heat shrink-wrap an ultrasonic ping sensor, mount it on top the hull and use it for obstacle avoidance?  Will the chirp and echo work underwater?

The problem with taking transducers designed for air and using them underwater is that you get a very bad acoustic impedance match. So very little of the ultrasonic energy that the transducer generates get transmitted into the water, and very little of the reflected energy in the water makes it back to the transducer. It's the same reason as why when you swim underwater, you can't hear the noise above the surface.
« Last Edit: January 18, 2013, 06:10:51 pm by dc42 » Logged

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I'd like to achieve 4.5 foot depth underwater.

Are your sender and receiver going to be directly on top of each other, or do you also have a horizontal distance to consider?

Let's say it's going to be in a hotel indoor pool.  Also I'm not going to be on the edge of the water surface with the remote.  I'm going to be standing with the remote 4 feet above water.  I know the IR receiver works in any direction horizontal, vertical, diagonal at least indoors with a direct line of sight, so I don't understand why I'm asked how much horizontal I'm aiming for.  To give an answer though, I would like 10 feet out from pool edge.
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I'd like to achieve 4.5 foot depth underwater.  I thought a BT module or WIFI board would work fine sealed in a submarine.  Radio communication reflects off water? Also, what if I heat shrink-wrap an ultrasonic ping sensor, mount it on top the hull and use it for obstacle avoidance?  Will the chirp and echo work underwater?

Natures warning sign: If any of that worked, you would see a lot of projects already using it.
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Consider the daffodil. And while you're doing that, I'll be over here, looking through your stuff.   smiley-cool

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so I don't understand why I'm asked how much horizontal I'm aiming for
Pythagoras.
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How does IR cope if the signal is sent under water to begin with?
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Lol!  Perhaps there was a nicer way for me to ask.  sorry, I did give an answer of 10ft.  Perhaps the IR signal refracts off the water or gets construed entering the water.  Beats me how IR copes with signals under water. It probably won't work well.  I did see a RC submarine once, so I wonder if that was just automatized to just float around.  Maybe the best idea would be to have a submarine with tube and a float where the BT module would be placed.  I'll run the BT module's wires down the tube to the submarine. That way it can be BT radio controlled and still be a stealthy spy bot. smiley-mr-green  
« Last Edit: January 18, 2013, 06:37:09 pm by encryptor » Logged

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Maybe the best idea would be to have a submarine with tube and a float where the BT module would be placed.  I'll run the BT module's wires down the tube to the submarine. That way it can be BT radio controlled and still be a stealthy spy bot. smiley-mr-green  

That strikes me as a far more practical idea from the technical point of view, you will still need to do some pretty good water proofing though.

Given the implication that you are planning to use this in a swimming pool to spy on people using the pool, I have to say that I would expect the swimmers and hotel management to take a very dim view of that. It might only be intended as a bit of fun, but in the wrong circumstances I think you could get into some serious trouble.
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