I have a project in mind and I would appreciate some advise on what approach to take.
Project overview:
It involves dredging... We use a "plough" type dredge bucket that we can lower & raise with a winch.
We lower the bucket onto the riverbed and drag sediments into the stream. We dredge to a maximum depht of 24 meters.
I would be nice if we somehow could detect how deep the bucket exactly is beneath the surface....
At first glance I tought I only needed an Arduino with and a depth sensor like this one: paroscientific.com/depthsensors.htm#181kt , enclosed with a battery pack in a sturdy container attached to the bucket.
But then I got stuck:
how to transmit wireless data trouhg 24m of water. Obviously the most frequent used systems (Xbee, Bleutooth, Wifi) are not suited for this application, unless I can find an open source solution I will be forced to use something like this: dspcomm.com/products_aquanetwork.html
Anybody has experience with AquaNetwork hardware ? Or knowledge of any other wireless data communication system that meet my demands ?
I thinker about integrating some kind of IMU board so that I would be able to tell exactly what the bucket was doing down there in terms of roll pitch and yaw. I figure that 2 axis can be derived from gravity, but
-if I want to know the buckets "heading" then I need to have a working compass module down there.
Will a compass be able to find north if it is enclosed in a metal container and submerged say 25m ?
-if I want to know where exactly the bucket is relative to it's towing ship then I need a working GPS
receiver module on the bucket, I doubt a gps module can find satellites in these conditions...
25 metres is not an inconsiderable depth, with significant hydrostatic overpressure before you've taken into account dynamic pressure from motion through the water, plus the inevitable knocks and bumps.
You could use an ABS case like a Pelican or Otter, but presumably the bucket is still metal, so that is going to make your compass tricky.
Also, any pressure sensor will require a hole in the case, which is bound to be a source of leaks and potential weakness.
I honestly think you're outside of Arduino territory here.
Hello sluiswacht,
nice project. Are you working in limnology?
Why wireless? You have the bucket's rope already to put a tiny cable to it. I would go for serial communication, maybe with MAX 232 to transmit it to a surface Arduino with a display. I am sure this is not to hard to establish.
The positioning stuff seems to be complicated, but why not give it a try with the IMU; the exact location is a challenge I'd like to avoid.
I am working on a similar project (underwater, measurement of various parameters, Arduino) and currently trying to put a MS5541 depth sensor (measures up to 14 bar) to an Arduino, it is not too expensive (approx 25€) and it should work soon.
Arduino gave me an easy entry into a whole new world of fascinating possibilities designing my own sensors and little helpers in scientific work; so yeah, it is maybe a little out of territory (since Arduino was intended to work for artists and... I forgot), but why not extend the borders a little ?
@ AWOL : I know how to mount the pressure sensor leakfree, that's not an issue (as long as I can use metal for the housing). The depth IS considerable in terms of reliable wireless data communication.
@ GODO: lymnology ? No, just trying to keep sediment deposition due to "tidal pumping" within limits.
Why wireless ? Well for a starters the bucket's hoist cable is rolled up onto a winch drum, if we mark the cable with spray paint to have some primitive indication of depth then those markings wear of in a few hours, no communication cable will survive this environment.
We also tried to measure depth with a secondary cable on a spring loaded drum but the currents and the wash from the propellers tend to pull the cable no matter how much spring load we apply. A motorized drum with an adjustable slip-clutch may solve that but the bucket normally is about 10m behind the towing boat so the cable measures depth at an angle and therefore not accurate...
I could route a cable to the bucket in an alternative way but I have my doubts about durability, as the bucket gets dragged trough sediment, rocks, and all kinds of debris, wireless is the most desirable option.
Oh and Arduino's open up far to many possibilities to narrow their "territory" down to artistic or leisure applications.
Example: I have an Arduino Mega with an Ethernet shield, it measures various temperatures, pressures and rpm's on and around our engines. The Arduino streams the sensor data on our LAN, our PC's display the values in a "virtual dashboard" made with PCMSCAN.
Back to the bucket now. If a compass is not able to find north, it is obvious that a GPS will not be able to fix position, I will settle for tilt and roll data that can be retrieved from gravity.
What if I would enclose a communication module in epoxy resin and attach it outside the metal casing, would Xbee or Wifi data be capable of reaching the surface ?
What if I would enclose a communication module in epoxy resin and attach it outside the metal casing, would Xbee or Wifi data be capable of reaching the surface ?
We also tried to measure depth with a secondary cable on a spring loaded drum but the currents and the wash from the propellers tend to pull the cable no matter how much spring load we apply. A motorized drum with an adjustable slip-clutch may solve that but the bucket normally is about 10m behind the towing boat so the cable measures depth at an angle and therefore not accurate.
Just a thought: Can you place the bucket besides (or before) the boat? so it does feels less the wash of the propellers?
Water is a good conductor of sound.
By using an ultrasonic transmitter in the bucket and taking readings from 3 receivers, you could pulse at
regular intervals, compare the time it takes to reach each sensor/distance to each sensor and calculate the transmitters position.
I do wonder how noisy the surrounding will be though.
What if I would enclose a communication module in epoxy resin and attach it outside the metal casing, would Xbee or Wifi data be capable of reaching the surface ?
No there is not. This is called cavitation noise and covers the whole spectrum. There are peaks and troughs in the spectrum but not nulls, also these change over time.
Its is the way that submarines can tell what surface ships there are over them. The signature is unique to each ship so from the noise you can identify the ship's name providing you have its sonic fingerprint.
How clear is the water? I guess the dredging part of this kind of answers my question but just in case..... How about something using blue LEDs?
Or alternatively - would it be possible to have a pressure sensor / IMU on the bucket with a cable/line running up to a buoy on the surface? The buoy could handle the wireless comms back to the boat and perhaps GPS?
I have read somewhere that for underwater data communication acoustic is "the only viable way" so I will have to go with that.
However cavitational noise may block any and all datacomm (very good point made by grumpy_mike), I will contact aquanet and ask them about that.
It is NOT possible to reposition the bucket in front or beside the boat, it is hoisted by a boom on the aft deck and dragged by 2 lines attached to the sides of the boat.
Due to high sediment concentrations LED communication is not viable. A line to a surface buoy is also a problem: to little slack and the buoy gets pulled below the surface, too much slack and it will drift too far to provide accurate positioning info. As dredging depth varies on track, a fixed lengt cable will allway be too short or too long, and when the bucket is hoisted the buoy will drift with the current.
I was thinking of a sprung reel going up to the buoy (complex) or alternatively a counterweight. So line up from the bucket to the buoy, through an eye and back down with a suitable weight on the end. The counterweight would keep the line taught without any mechnical complexity. Not sure if I've explained very well but I can draw a picture later if you like
Grumpy_Mike:
No there is not. This is called cavitation noise and covers the whole spectrum.
This strikes me as a little fishy. I don't doubt that there is all sorts of racket due to equipment and whatnot. Nevertheless things like depth finders do seem to operate in the real world, even on power boats, even while under way.
My personal suggestion is to use conventional depth sensors, and/or whatever other sensors you can get working, and transmit telemetry via ultrasonic transducers.
Something like a 30Khz/45Khz FSK scheme should be able to get you 300 to 500 BPS fairly reliably.
?