I’m wondering if anyone here could give me suggestions on what would be the best way to build a wireless underwater camera.
What I’m looking to do is build a camera assembly that will roll along tracks underwater. We hope to have it wireless, transmitting back to a base station above water where the video stream will be editted on a PC. This is to be used for stroke analysis for competitive swimmers.
I know I can find some wireless cameras for reasonable prices, but will I be able to transmit the signal effectively from underwater to above water? The range only has to be 60 meters or a little less. If not, would it be sensible to run an antenna from the camera assembly to above water?
Also, just to tack on another related question, we hope to figure out a method where we’ll be able to detect the swimmer’s position during analysis. We’re thinking of placing a second transmitter on the swimmer, and then having an antenna at each end of the pool. From there I’m hoping we’ll have the capability to calculate the swimmer’s position based on the relative strengths of the signals being received at each antenna.
Very low frequencies can penetrate water. There are some very low frequency arrays, I believe on is in Washington state, that can communicate world-wide with submarines under water. However, they are very limited in bandwidth and communicate by Morse, or similar, codes. They might even use just a keyed carrier rather than modulation.
As to higher frequencies for short ranges, get a garage door opener t/r unit. Put it in a waterproof enclosure with an antenna and try it.
Have you considered using sound waves? Sonar works pretty well for locating underwater objects and keying it for camera control, with proper filtering to cut out incidental background noise, should work.
Why make it wireless? I think that’s just creating complications for yourself.
Wireless requires additional electronics to convert the video to a wireless transmission, then a receiver on the other end. Plus extra stuff to transmit thru water, which blocks a large part of the RF spectrum. And additional power for all of this, etc.
On the other hand, waterproof cables have existed since the first telegraph cable across the Atlantic, back in the Civil War times. And modern cables are much smaller, lighter and more flexible. Seems like a cable attached in the center of poolside, with 30 meters of slack to reach either end, would be much simpler and more reliable to work with. Put a good waterproof connector on the end, and you can even have spare cables on hand in case of problems or accidents.
I’d seriously reconsider why you want it wireless.
Hrmmm… I’m really not up to going as high tech as you’ve suggested David. I know there are transmitters on subs transmitting at extremely low frequencies, but this is way beyond me.
We’re really hoping to use an off the shelf solution for the television transmission/reception. If we’re not able to get it transmitting from below to above water, we’re probably simply going to run an antenna from the camera to above water. Since the camera will probably not be more than 3 or 4 feet under water, this won’t be a problem (I hope).
Still not sure how we can possibly detect the swimmer’s speed/position though. I want to avoid coding anything to attempt to have the PC determine position, so that certainly rules out one possibility.
I think echo-location is a better way of determining swimmer position than transmitted signal strength. I can’t think of anything that works on the latter principal, but I can get a cheap fishfinder for 50$ that works the first way. I’d check out using that type of technology if I were you.
P.S. - for the camera thing - wireless would also mean having a power supply onboard. Water is opaque in the higher frequency, higher bandwidth range, but to what degree I don’t know. 5 feet of water doesn’t seem like it should pose much of a problem if you choose to seal the ends of regular wire inside some type of box.
Yep, I’ve been thinking about the viability of wireless. You’re right, it’d either require an onboard power supply, or a rolling power supply above water, both ugly options. I suppose we were mainly thinking of wireless for the coolness factor.
BTW, just so this doesn’t sound quite so much like a pipe dream, last year we built an underwater camera for the same purpose. Now that was an ugly setup. Made mainly from ABS pipe, built on a four wheeled dolly, with one camera above and one below water. The ABS was a good idea, quick build time and very adjustable, but still…
Anyway, so I’m inclined to agree with you all at this point: wired will be far cheaper, easier, and more reliable. So I think I’ll be spending some time tomorrow looking at our options for wired setups.
Onto the swimmer speed/position thing: Nanoda, I think the fish finder idea’s a good option, but… We want to be able to use the swimmer’s position to be able to graph his speed all the way across the pool. This is because for stroke analysis we need to know if possibly the swimmer’s reversing slightly during the breaststroke, etc. So while a fish finder/echolocation setup would be good for rough position, I’m not sure that the refresh rate would be good enough to work for our purposes. As well, I need to look into the ranges possible with a fish finder; as I’ve said, their’s the possibility that this may be used in a pool 50m long (the 60m range earlier was to include a bit of distance from the edge of the pool).
Well, thank you all for your help, I’d love to hear if anyone’s got any more ideas/suggestions for me. I hope to sort out the details as completely as possible before we begin this build.
If you set a line of buoys along the swimmer´s path you can use the video to extract the position; just put label on the buoys every meter, for example.
Ale, we’ve considered that option, but we’re looking to avoid coding any image recognition software. We’d like to have this be a completely automated process.
I looked into the fish finder possibility. It seems there wouldn’t be a problem with range, but I’m not sure we will be able to find a way to interface the fish finder to a PC to automate the process. As well, I haven’t been able to find any data on the refresh rates for fish finders.
If you’re filming him from start to finish, why would you need any locator? As long the footage is time keyed, couldn’t you just look at it in slo-mo/frame-by-frame to analyse his position and speed?
Trigonal Planar, we’re hoping to have the process automated so that when we create the final video analysis for the swimmer it will have audio commentary as well as a graph of the swimmer’s speed all through the stroke cycle. This will allow us to determine if for instance the swimmer is pulling backwards slightly during his breaststroke.
While we could simply view it frame by frame and do this by hand, this would become both tedious and time-consuming when we do a hundred swimmers in a day.
I was going to suggest the possibility of GPS devices, but I think the public ones are only accurate to about 20’ or so. That’s probably not close enough for your needs, right?
Possibly you could build your own local GPS system, by putting your own ‘homing’ transmitters in 3-4 locations, like at the corners of the pool. But you’d need to be very precise about the distances between them. And the problem of getting software for this system still remains.
[Could you give us some specifics on what you need, please:
How frequently (in seconds) do you need locations?
How much distance will a swimmer travel in that time period.
How accurate (+ or - how many feet/meters) do you need the location to be?]
Another possibility might be a board that you hang over poolside, just above the water, containing light beams & photocells located every foot or so along it, connected to a computer that records when each light beam is crossed. This assumes that there is only 1 swimmer in the pool at a time, and that the swimmer comes up out of the water enough to break the light beam, and that there aren’t waves that would break other light beams. I don’t know if those conditions could be met. Also, this involves more equipment, and it might be tricky to adjust the height just right.
A modification might be to put the light beam on the swimmer – a laser pointer that they strap to a relatively stable part of their body, like the back of their waist; and just have a blanket of photocells along the side wired to the computer. But that could take a large number of photocells.
t-bonham: I’m thinking that your idea with a laser mounted on the swimmer is good, but just not feasible for us.
We’ve decided we need an absolute minimum data refresh rate of 10 hz, although preferably 100 hz. I’m not sure of how far a swimmer will move in a second, but I’d imagine under 5 meters. We don’t necessarily need the location to be accurate, but the speed does need to be reasonably accurate.
The numbers I’m thinking of:
100 updates a second, swimmer moves 5cm between updates, accurate to +/- 2cm per update. Is this going to be at all possible with reasonable materials?
While I imagine I could do well with a blanket of photocells, probably needing tubular light shields for each one, this is really not going to be within our timeline.
If we’re absolutely unable to find a method for speed determination that will work for us, we’ll simply leave it out of the project. We’d really like it, and it would be great for analysis, but we can’t afford what it would take for most of the suggestions so far.
Thinking about this some more, for simplicity of equipment, and keeping the cost low, you should look for transmitter - receiver type equipment. One or 2 ‘base’ stations, and maybe some kind of transmitter or reflector that can be placed on the swimmer. Avoid the large blanket of photocells & lightbeams methods – too unweildy for this application (and probably too costly).
What about some kind of device like a police radar that could be positioned at the end of the lane, and report the speed of the swimmer every second or so? (Skip location altogether, go directly to speed reporting!) Are radar units available which are accurate to such small tolerances, over a short length like a swimming pool?
Also, what about the kind of back-up alarms that are sometimes fitted on trucks nowadays? Not the annoying beepers, the sonar/ultrasound units that tell the driver how many feet he is from the loading dock. Are these possibly accurate enough for your use?
P.S. If you really have a swimmer who can travel 5cm/centi-second, forget all this measuring crap immediately and concentrate on getting this guy to the next Olympic! That speed is about 2-1/2 times the current world record!
5 meters per second!? that ain´t a swimmer, it´s a friiging torpedo!
OK, how about this (warning, I´ll get into brain-storm mode now, very weird ideas my come out)
Attach a string to the swimmers waist, connect the other extreme to a reel that actuates on an odometer (or something like it)
Make a supersonic pulse transmitter (A) (you know, like that PING!!! sonar thingy in subs ) it´s not difficult to make with a few electronic components, install a receiver/transmitter on the opposite side of the pool (B) , the transmitter also should have a receiver I think the word is transceiver, B sends a signal and starts counting, A catches it and sends a response signal, B catches it and sends the time to a computer, it´s like a sonar, but more reliable. Any decent electronics geek should be able to come up with a working design.
Oh well, that´s all I can think by now, I´m more prolific usually, but it´s 2AM…
Hrmm… I suppose I was a little off on the speed of a swimmer. I’m not too into the swimming aspect of this, just the mechanical/electrical components. Someone else here knows the swimming stuff far better than I. (Although possibly 5 m/s isn’t completely unreasonable, but only for a very short portion of the stroke?)
t-bonham, Ale, you both seem to have the same idea for something along the lines of a sonar. Send a signal along the pool, then somehow have it reflect off the swimmer back to the receivers. Possibly have an omnidirectional transmitter on the swimmer then have a detector at each end, and have a device that will compare the signals from the receivers to find position, send the calculated position to the PC to be converted to speed?
Ale, you’ve also hit upon an idea I’m told has been done in Calgary (Alberta, Canada). A swim coach there has come up with a device that measures the speed that the string (tied to the swimmer) comes off the reel, then he uses that to determine speed at different points in the stroke cycle. While this is a simple solution to implement, it isn’t as accurate as we’d like. It would be hard to set it up to measure any times that the swimmer may be moving backwards, while it also adds some drag to the swimmer, affecting their stroke and speed.
