Underwater Personal sonar devices

[jreilly2]

Hello all,
I'm working on a project and have hit a technical wall. I am looking at using a sonar unit inside of swimming pools that will help alert blind swimmers as to location of obstacles and walls. I am having issues with medium transfer, as well as cost. I need a inexpensive, short-range active sonar unit that can trip a vibrating wrist band. Any ideas or suggestions would be greatly greatly appreciated!
Jeff Reilly

[madsci1016]

This is going to be a tough one.

I work for the Navy, and while i'm not a sonar expert, i work with the experts and know a few things.

Sonar in closed bodies of water is a very bad thing. You get a lot of interference called Multi-Path. It take a lot of expensive signal processing hardware to understand the data coming from a Sonar head.

They only thing i can recommend, is look for really cheap marine depth finders.

[jreilly2]

Thats kind of what I was thinking would happen. Any thoughts on another tech. that would fit the bill? I have been trying to build my own 'invisible fence' rig, but have been facing issues with proximity error and the fact that that would require a signal antenna around the pool. Thanks again for the reply!

[Soeren]

Hi.

Any thoughts on another tech. that would fit the bill?

Ultrasound (for over the water) might work if it can be water proofed, but as with sonar, strap it to eg. the head of a swimmer and you have no chance of telling where it points.

A speaker at every corner of the pool, playing a soft continuous tone, might be used for direction by ear, but will be unbearable to most and don't solve for swimmers colliding (but if they're all told to sing while swimming ).

It's not an easy task you have set yourself and not knowing whether it's for one person or several, or if there's a seeing person for each blind person, that could perhaps use a "remote control" with a vibe at each wrist to sort of guide them, it's hard to tell if there's a cheap solution.

[jreilly2]

I was discussing with a freind of mine the idea of trying to adapt a radar gun, which can determine distance. Could this idea be modded to work A) underwater, B) lose the directional requirement that radar requires. What i mean is I don't want a person to need to be pointing directly at the object in front of them.

[jreilly2]

Also, the primary goal in this project to promote autonomy for the blind swimmer?

[Soeren]

I was discussing with a freind of mine the idea of trying to adapt a radar gun, which can determine distance. Could this idea be modded to work A) underwater,

Not unless you're a top grade DSP programmer (and that might not even do it), you'd get an echo from whatever was enclosing it and it would be much "louder" than more distant echoes.

B) lose the directional requirement that radar requires. What i mean is I don't want a person to need to be pointing directly at the object in front of them.

Weak radar works due to this directivity.
You could dispense of the wave guide and get a close to 360° mm-wave cooking the protein of the swimmers eye white like boiled egg white (doesn't matter much if he's blind in the first place, but any seeing person close by might not be too keen on the idea).
However, there might not be enough signal returned and if there was, any swimmer behind the swimmer in question would register if within distance, without being an obstacle at all.

Did you consider going ghetto on this and perhaps use a (number of) feeler "antenna" of slightly bend piano wire with a ping-pong ball in the end?

[jreilly2]

The ghetto method actually was done by Notre Dame. It works well for lap swimming but not recreational swimming. Imagine a laneline of tentacles. Everytime I think of a practical way to shirnk the range of sonar, I realize that fact that it will detect the bottom before any obstacle if the pool is shallow.

[jreilly2]

One question i have about the confinement of a pool is the bottom. It will most likely be the nearest thing to you all the time,  how do you avoid the actuator from alerting the swimmer when the sonar unit detects the floor?

[Asellith]

Just tossing an idea out but for short distances wouldn't something like a IR sensor work underwater. It would defuse really fast so might not work. Maybe a line laser set to sweep up and down and some kind of detector on the swimmer that reacted when it saw the laser. If the laser travels to far in the water to work you could set the sweep to a specific period and monitor the amount of time it takes for each instance of laser to hit the sensors then it can get some idea of distance.

Just some random brainstorming for you...

[StratCat]

Hello all,
I'm working on a project and have hit a technical wall. I am looking at using a sonar unit inside of swimming pools that will help alert blind swimmers as to location of obstacles and walls. I am having issues with medium transfer, as well as cost. I need a inexpensive, short-range active sonar unit that can trip a vibrating wrist band. Any ideas or suggestions would be greatly greatly appreciated!
Jeff Reilly

Hey Jeff,

Having known a few people with visual impairments and possessing the over-active imagination that I do, I thought I might engage in a little musing.

There are both fixed and dynamic objects to avoid in a blind swimmer's field of operation. So you need a system that will track both the swimmer in relation to the fixed objects (the sides and bottom of the pool, useful pool fixtures like ladders, swimming lanes and various other obstacles) and track the locations and movements of the dynamic objects, whether another swimmer or other floating or submerged objects.

madsci1016 is correct in that sonar is not a good solution. IR as a solution is also doubtful. You need something that works in both air and water with identical results. You would need a system that could inform the blind swimmer of the location of other swimmers, obstacles and the boundaries of the pool.

In my mind, radio comes to the fore. It is a tried and true method. Resolving the location and movement of the swimmer in relation to the pool and other swimmers is fairly easy using radio. That leaves only tracking random dynamic or static objects independent of the radio system that may or may not be in the pool (furniture, empty beer kegs, mermaids etc.). I'll come back to the problem of random obstacles later.

I thought about the wrist band you mentioned and think it might be  inadequate to the task of yielding meaningful feedback. Yes, it gives a proximity warning, but is that enough? For me, it doesn't give the swimmer any readily usable feedback in regard to collision avoidance or course correction. Just knowing that you are about to hit something isn't enough information. Because being suspended in a darkened, weightless environment with the knowledge that you are about to collide with someone or something, can quickly cause disorientation. If you get spun around, how do you reorient to your original course?

So why not create a central information processing system and customize radio location and fixed object feedback information to be transmitted to individual units. The information on object location and movement can be readily translated to directional audio feedback for each individual swimmer via a 3d dataset. Object and swimmer identification can be easily achieved by tagging each with a different and uniquely identifiable sound.

I'm wondering if you would have to track the attitude of the swimmer's headset in relation to the environment to accurately reproduce a sound 'image' of the swimmer's surroundings. Perhaps embedding multiple waterproof ear-buds into the earpieces of the headset might be a solution. But this is a fairly small challenge when compared to using sonar in a small body of water, surrounded by thrashing, noisy swimmers and hard, sound-reflective surfaces.

Headset attitude awareness could be accomplished with an antenna array included in the headset. Attitude is just another data set to transmit and process.

With the method I describe, the swimmer would be able to uniquely identify other swimmers and objects as well as their proximity, relative location, direction of movement and speed. Extending a collision zone behind the swimmer based on the swimmer's approximate height, the headset attitude, direction of movement and speed (or lack thereof) is another thought.

Known static objects can be uniquely defined in the data set that describes the fixed environment and added to each sound 'image' update that is transmitted to the swimmer. The location of fixtures like diving boards, ladders and stairs could then be easily discerned. This is more than just useful information. It is potentially life-saving.

Radio is low tech, cheap and easy. PCs with enough processing and storage capabilities to help realize this solution are likewise cheap and plentiful. Waterproofing the headsets that carry the radio transmitters, receivers, antennas, batteries and earphones is likewise easy and inexpensive.

OK, let's summarize: Gather location information on swimmers via radio tracking, store it, update it at regular intervals, calculate a current audio 'image' including all known fixed and dynamic objects, transmit a sound snapshot that is properly oriented to each unit's attitude - then update all of the above several times a second.

While there are some considerable programming requirements, most of the code segments have already been written by someone, somewhere. You just have to find them and conform them to your project. All in all, it seems doable and cost effective.

Now, back to the 'random obstacles' mentioned earlier. Another method worth exploring might be raster scanning lasers as mentioned by Asellith. That method, as an addition to the radio location method described above, would account for randomly added obstacles in the pool not tagged by radio - making for a much more robust solution. But it also adds another layer of complexity. Just depends are how far you want to go...

Like I said at the start, just some musings of an over-active imagination. Tell me what you think.

Phillip

[StratCat]

After a little looking, I see that mine is not a new concept. Still...

http://cordis.europa.eu/ictresults/index.cfm?section=news&tpl=article&ID=90729

[codiak]

After a little looking, I see that mine is not a new concept. Still...

http://cordis.europa.eu/ictresults/index.cfm?section=news&tpl=article&ID=90729

And there is an affordable handheld unit for divers
http://www.leisurepro.com/Prod/AQUDSS.html?kbid=1807&sub=8841914

Not as much fun as building it nor guarenteed as suitable for the application in mind...
but perhaps not so expensive as to hack it for parts and ideas

[Admin]

admin to the rescue!

This is what I use on my robot fish:
http://www.maxbotix.com/BUY_NOW.html#MaxSonar-WRC

Now, these are only 'water resistant', so you need to waterproof them. After soldering wires to the sonar, completely coat the end with RTV to waterproof the electrical connections.

Now on the other side with the transducer, in the gap, fill it with a very soft RTV to waterproof that end. Wallah!

Keep in mind that sound is 4.1x faster in water, changing the sensor output, so you'll have to account for that in your software. The sensor has amazing range underwater, much better than in air.

I'll write a tutorial on this with pictures, one day . . .

[knossos]

I would love to see that tutorial, as one of my plans for the future (once i have much more robotics experience under my belt) is for an amphibious autonomous robot.

[madsci1016]

I'll write a tutorial on this with pictures, one day . . .

I would love to see that tutorial, as one of my plans for the future (once i have much more robotics experience under my belt) is for an amphibious autonomous robot.

Ditto. That's something I would want as well, and there's not much on the web for something similar. Definitely hack-a-day worthy, maybe something to start off the upcoming SOR blog and get it noticed around the web.

[kikko_fr]

Hi there,

Has there been updates about the tutorial Admin talked about ?
I'm really interested in knowing how to get a waterproof sonar sensor out of a basic water resistant maxbotix sonar.

Thank you very much all for sharing!

[Admin]

Has there been updates about the tutorial Admin talked about ?
I'm really interested in knowing how to get a waterproof sonar sensor out of a basic water resistant maxbotix sonar.

I made a video that shows how to do it almost a year ago, but I never edited it or uploaded it to youtube . . . mostly busy with other priorities . . .

I'm too busy for the next month, but I'll try to get around to it afterwards when I can. Sorry!

[kikko_fr]

Hey!

Ok no worries! I'll give it a try on my own and I know where to ask if I have any questions

Thanks

[kikko_fr]

Hi!

So I've received my XL-MaxSonar-WR and can't wait to do the first tests!

I've been a little surprise to read that the protection code of the sonar is actually IP67 which on the wikipedia defines as :
- No ingress of dust; complete protection against contact
- Ingress of water in harmful quantity shall not be possible when the enclosure is immersed in water under defined conditions of pressure and time (up to 1 m of submersion).
Test duration: 30 minutes
Immersion at depth of 1m

So, since it will barelly immerged (10/20cm max), I'm wondering if I still need to fill the gap of the transducer with RTV with this model? I can see an orange seal that seems to be there for that?

Thanks!

[Admin]

I finally got around to uploading the waterproof sonar video.

Enjoy!

Waterproof Robot Sonar Tutorial