Monitoring Water Current direction and speed

[haklesup]

I don't see why generating power from current flow would be difficult. You would need a significant flow and a bigger propeller and generator than you would if you were just sensing speed. I am not sure if you would sacrifice accuracy because a generator would have more torque resistance. Such a generator might cost more than maintaining a battery though. Depends on your budget and the operating conditions.

As for choosing a processor start by defining the specs then survey several manufacturers to see what fits. For example you need at least one A/D, 12 bits sounds good but 16 will do better. 2 or 4 A/D converters would be great. I/O? 8 bits or 16 bits and how about interface to the real world. A built in serial port you can either buffer for USB or wire to the IR LED or an optical port (TosLink cable) would also make things easier. Now consider internal program memory and how much memory you need to buffer data. Will it be internal to the chip or do you add external memory.

The fewer chips you need, the easier it will be to build, try to find a chip that has it all in one but not too much more than you need. Once you have your head around the requirement try looking at some manufacturer websites like this one

http://www.microchip.com/stellent/idcpl ... odeId=2551

http://www.microchip.com/stellent/idcpl ... &nodeId=75

Click on the Sensor link near the bottom of the list and you'll see a few candidates. The dsPIC30F3012 at $3.64 each looks good. It has lots of memory, I/O,A/D converters and interface all built in. They also have RF, and battery control chips in their product line. Nice thing about sticking to one maker is you will have better luck with support if you should need some for your design.

And this was just one of at least a dozen vendors.

[Smoke_Maker]

This one is simple and cheap, Hobo has data loggers with external inputs (0 to 5 volts) with time stamps, for flow direction use house magnetic alarm switches (reed switches) and a magnetic on the direction vane, every 30 minutes the unit wakes up and checks temp, direction and speed.

Hobo
http://www.microdaq.com/occ/h8/tempexternal.php

[Deal]

I would start on the water side of the project and focus down on the information you want to gather. If your 'lagoon' is tidal then you might be able to gather water current data for two or four events per day. If you are looking for 'stream' data then storm air events might be useful for correlation. Aided by info from this N+V site, I built a tide monitor to measure water height from my dock using a Parallax ping sensor (works well). My experience has been that the environmental conditions need to be tackled first. For instance, similar to your project, I wanted to gather current information and built a broomstick vane which floats just below the surface (reducing wind and wave) in a 360* arc under the dock surface. The barnacle-brackish organic growth quickly weighted into deeper waters. Sealing electronics for year-round function is not easy considering bugs, ice, condensation, violent storms, flood water, organic growth. I would start with one single sensor pack designed to gather minimum variable data (winter is a good season to start test flights). This forum is a good source of brainpower. I would also tap into the experience of scientific organizations that gather water condition data. Talk to crabbers (I live on the Chesapeake) about their buoys and maintenance. The Coast Guard and boating safety and insurance liability are also important considerations. Fair'waters' and keep us posted.

[haklesup]

Deal brings up a valid point about packaging the electronics for wet enviornment. I have seen at least two good methods for this.

At or near the surface, I might use a modified Pelican case. The boxes are inherently waterproof and are easy to drill and fit waterproof bulkhead connectors and passthroughs. Since it is empty inside it will want to float and wouldn't be good at great depth but offers the convenience of easily opening it for access.

Below the surface, I see electronics sealed into PVC or ABS plumbing pipe. With the vast choice of fittings and sizes, you can construct something quite water tight with minimal air volume inside.

At greater depth, you should backfill the electronics with either mineral oil or silicone RTV to provent any water intrusion. Obviously if you use Iol, you need hermetic components but this still allows access. Potting in epoxy or silicone prevents most service if required.

Plan your sensor package, the DAQ system and your method of data retrieval seperately but in parallel so they fit together nicely and perform your function well when you are done.

Do a nice job and you can offer it as a finished product and make all your money back.

Are you looking at this as a DIY from scratch project or as a system integration where you buy predesigned components and make them work together. The latter is faster but much more expensive.

[bdickens]

Thanks to all who posted/emailed. At a couple of folks suggestions, I'm going with a hydrodynamic shape, (a flat whale with a hole in the middle) that rotates around a fixed pole (tripod base). The tail of the body will be a propeller that will both act as a tail and generate electrical power for the unit. That assumes I can both generate power and measure the speed of the shaft. If not, I'll run a seperate turbine for speed. The "nose" will have a solid state compass, the pole a grey-encoder.

We will be measuring direction, speed, temperature, and if the pressure sensor works as expected, depth. I'm going to tinker with clarity (optically).

My local biologists (Dauphin Island) recommended sampling every 30 minutes. I guess, I'm going to wait and see how much power my test rig generates before I make any commitments there. I've also got some ideas around continuous sampling and storage I'd like to try. Uplink is still open. Might be trying sound based, which would allow me to keep them under water and "invisible".

Process from here: I just cobbled together a generator rig and a stuck it in the water outside the house. I'll have an idea how much power my 8 inch prop will generate. As suggested, I'll probably focus on the water side and the sensors, then get serious once I see how my power budget goes. My OOPIC will do fine for now. I may learn more about the Propeller chip.

Thanks for all the help. In the next 3 months, I'm going to be back with some questions. (no doubt) including maximizing a micro generator, but again, thanks for the comments.