scuba dive compass with return function

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turtle dude:
i would only be looking a range of 180-200m if possible?

I'd have to run some numbers but I would think that distance do-able. I'll see if I can re-find that paper I saw on underwater absorption and scattering.

turtle dude:
The receivers would be mounted on the out side of the rebreather case (i might even mount them in seperate little housings with leads going back to the control unit to give more flexibility with location).

the transmitter would be mounted approx 5-10m above the wreck attached to the shot line.

There's 2 questions here, the location of the transmitter relative to the coverage area and the best location for the receive hydrophones;

Re: the first … You can think of the beacon transmitter, using multiple “speakers” acting like a big search light, consisting of multiple flashlights. The diver needs to be in the area “lit up” by the search light. The transmitters you chose have a narrow “vertical” beamwidth, perhaps 15 deg (IIRC). I was surprised it wasn’t the same as the “horizontal” beamwidth but there you go. So the narrower the beam, the higher up from the sea floor the transmitter needs to be to “light up” all of the wreck and it’s immediate surroundings. See the diagram for the math.

In the above a single transmitter/speaker is aimed (blue line) just off vertically downward by 1/2 of it’s ([half power full) beamwidth. The beamwidth is indicated by the red lines. It will cover out to a distance R from directly below the beacon. As you can also see the distance from the beacon to the furthest point out in the coverage area is > R and > H. This is the distance to be used in calculations of how far away can/must the beacon be heard, = sqrt(R^2 + H^2).

re: the second … will mounting the receive hydrophones on the rebreather block them from getting a signal when the diver is swimming towards the beacon ? Does the aiming of the hydrophones change if the diver if floating vertically vs horizontally ? I have to believe this is the case but I’m unsure how much it’ll matter.

turtle dude:
so would it be a case of fitting more transmitters (ie six instead of four) to get the 360° required cover? Also if i had more transmitters if there beams crossed would this start to cause issues?

You should be able to add more and get the coverage needed. I am assuming that each transmitter is just a speaker and needs an amplifier to drive it. That way you can add any “tweaking” needed to get all the transmitters in phase with circuitry btw a common 40 kHz oscillator and the individual amps for each transmitter/speaker. How many more transmitters/speakers are needed is another exercise in geometry. I might need a beer or 2 to make a good diagram of that, one that’s accurate. It’s been a while since I did conic sections. :mrgreen:

http://en.wikipedia.org/wiki/Conic_section](Beam diameter - Wikipedia)

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Hi

Sorry for the late reply, my head exploded after trying to read the artical on conic’s, haha, plus family and work has been manic at the moment.

attached is a pic of the rear of my unit, the only thing not attached is a small (3litre) cylinder either side.

The approx space I could achieve between receivers is 500mm vertically (or possibly 200mm horizontally if better).

I swim just off horizontal in a slightly head up position, so see no issues while swimming away from transmitter but not sure about when swimming towards it (which is obviously what im trying to achieve LOL).

Many thanks

Baz

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turtle dude:
Hi

Sorry for the late reply, my head exploded after trying to read the artical on conic’s,

Yeah, it took me a couple of MaiTais to get that properly (or near enough) figured out. Here's a plot (markings are in ft) of that result. What is shows is the acoustic power falling on the seafloor from your sender suspended 100' above the seafloor.

As you can see using a transducer that has a beamwidth of 60 deg by 15 deg leaves a lot of area outside of the ship not covered and since I would expected the sender to rotate as well as bob and sway due to wave action … well, it ain’t gonna work. You’ll need many more transducers to fill in the center area … or look for a transducer (really only a speaker/transmitter) that has a equal beamwidth in all directions and wider than 60 deg (if possible) and mount it facing directly downward.

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BTW the above plot is based on some shaky info I saw, where the beam of the device you listed was 60 deg (+/-15 deg) by 15 deg (+/- 7.5 deg). I haven’t found the manufacturer or seen specs from him. So let me assume that the beam is 60 x 60 deg wide, a typical cone. Then a single transmitter, aimed downward, still at the same 100’ above the seafloor would cover a circle (nice !) but w/a radius of only about 60’ (~20m) and you wanted 200m. So you need to;

  1. put more distance between the seafloor and the sender (is this even possible, are you diving this deep ?)

  2. find a transducer/speaker w/a wider beam

  3. use multiple transducers/speakers again

So I ask … what kind of radial distance vs depth is reasonable to assume ? Could you be in 20’ of water and want to direction find (D/F) out to 200 m ?

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And because I have the Excel file working …

Here’s what a possible pattern might be using your sender populated w/17 (!!) of the transmitters you’ve chosen, but this time w/each having a full 60 deg beamwidth (in all directions, aka a cone). Sixteen of the transmitters are arranged around the rim of the sender, angled 45 degrees up from downward. The last transmitter is aimed directly downward. As above, the sender is suspended 100’ above the seafloor and anywhere within the colored area would be considered to have (roughly) the same acoustic power at the seafloor. In places where the “beams” from the transmitters overlap, you can see it’s a bit darker color. I can just about claim out to 100m (radius) coverage with this scheme, though there are some areas where it’s less.

(click on to open)

And it also occurs to me that rather than phasing up all the individual transmitters and having them all “chirp” at the same time, you could just have one (or 2 or 4 non-overlapping) transmitter(s) “chirp” at time and cycle through them all to get the coverage needed. I figure if the whole cycle took 1 second, that’s a quick enough update time. The animated GIF below shows that process and gives you a better idea of how each transmitter covers what area.

(click on to open and animate)

Sounding a bit trickier than you first thought ? :twisted: :mrgreen:

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Mee_n_Mac:
Sounding a bit trickier than you first thought ? :twisted: :mrgreen:

Haha dosn’t it always!!!

I’ve been posting on some dive formus to see if anyone has more info about the Xios eyesea (ie what transmitter/receiver used), As I read somwere that it was removed from the market due to “military complications”. But as of yet no one has come back with anything. I even asked if anyone has a faulty unit laying about I could “look inside” :whistle:

your diagrams really helps, but it looks like I’ll need to really look into a much better speaker/transmitter rather than looking at a cheep one that looked nice?

many thanks for all your time any efforts so far, I’m on nights most of this week so hope to get chance to google some more transmitters.

Regards

Baz

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Came across this last night while looking for transmitters

http://my.fit.edu/~swood/THESIS_BOWLUS.pdf

I understand that the buoyed GPS system isn’t suitable for what I’m looking at but some of the other info looks intresting?

Regards

Baz.

28

The XIOS EyeSea is pretty much the same thing I has in mind, w/the exception that this system would only give bearing … not range to keep things simple. If you had transducers at both ends (sender and diver) then it could do range as well. I’ll have to read the rest of the article to see if there’s any ideas worth stealing.