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!
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.