Underwater sensor
Jonathan Allison
Posts: 96
I may be involved in a joint project where we are monitoring lobster fishing traps. A bs2 is to be used to record the data.
There are three main things that I need to record, water temperature, current speed, and lobster movement. For the movement perhaps there is something like a sounder with very low range, or possibly a motion detector.
Anyone have any tips / leads?
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Johnny
Gee Sarah, Thats a reeeaaally nice gradin' present.
I can't wait until Rickey sees that c***sucker!
- Bubbles
There are three main things that I need to record, water temperature, current speed, and lobster movement. For the movement perhaps there is something like a sounder with very low range, or possibly a motion detector.
Anyone have any tips / leads?
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Johnny
Gee Sarah, Thats a reeeaaally nice gradin' present.
I can't wait until Rickey sees that c***sucker!
- Bubbles
Comments
Dave
Do you need to count the Lobs'tas in the trap, going into the trap, and/or the little ones who go in and out many times?
You could have a trip switch·on the·entrance hole, that is spring loaded, and counts the number of Lobs'tas entering. (although you will know how many when you retreive the trap, to collect the "data" from the Stamp. There will be a corresponding number of "data" units crawling in the traps as well.
A little more information on the type of data needed will help.
Anything for an excuse to head "Downeast" A-Yuup
Alan Bradford
Plasma Technologies
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Johnny
Then you'll find out that lobsters can see IR and spray paint the mirror to avoid being detected.
You'll also need to avoid any external protrusions from the trap. Various studied have found that crustaceans find their way into the trap by moving their way around the outside until they find the opening. I'd be concerned that an external sensor pack, if too big, might created an impediment to the lobsters thus affecting the validity of the data.
Jim
Temp is easy enough....
Current speed....just use an impellor/propellor type of unit.· Our Hydrometric technicians use what would basically be similar to a wind speed sensor.· They also use doppler radars but the first option is slightly cheaper!
As far as entrance/exit to the trap....have a spring loaded mesh gate at the entrance to the trap.· When the lobster pushes through, the gate opens and triggers a switch.· Use chicken mesh maybe....and arrange it that it could swing both ways.·
Using IR down in the mirky depths of the ocean may not work.· (don't know what would happen to them at depth--isn't there a gas in those little capsules?).· Anyhow, mechanical counts might be better for 'false counts' as you'd have to put to IR sensors in the trap to determine direction and a lobster that lodges in the 'sensor area' might trigger a bunch of false counts.
Just making a guess....
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Steve
http://members.rogers.com/steve.brady
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
True, however you need to ensure that the mechanical sensors don't deter the bugs so that you get a skewed population count as a result of sensor. My question would be, how would the lobster know to push through at the location of the sensor, as apposed to other spots on the traps. Traps have a cone shaped entrance allowing the lobster into the trap without impediment.
Jim
I thought maybe 'chicken wire' would have large enough holes that would still 'look' like an opening for the lobsters.
And yes, if you make the 'gate' easy enough for a small lobster to open, then maybe the currents will trigger it too!
But the idea of the cone opening is to prevent these guys from getting out too easily....is it when the trap fills up that they are at the right level to walk out the opening?
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Steve
http://members.rogers.com/steve.brady
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
I agree with the IR concept, however, I am limited to power supply, I am thinking one of those 6 volt batteries commonly used for flash lights, they are about 3" x 3" x 4.5" I'm sure you know what I mean. How long would the 6 volt battery last I wonder, and if anyone knows of any formulas for figuring this out let me know.
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Johnny
I once found a chart in Radio Shack, but can't locate it now.
Anyway, once you find the Amp-hour rating, then you need to find out the average current needs of your project. Note if you 'pulse' the IR, it doesn't have to be on all the time, and you can get lots of power savings there.
So 20 Amp-Hours / 200 mA == 100 hours (all numbers made up here, but the equation is correct)
You'll also need to run your project with a 2940-5 regulator, as these are 'low-dropout' and will work with a 6-volt battery. Note also I believe the 'Lantern Cell' you are talking about is equivalent to 4 'D' cells, if that helps.
Also, make sure none of the net/mesh could get in the way of the IR beam... otherwise, the water current might make the net/mesh get in the way and cause a false reading.
Dave
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Johnny
Maybe you could have the contact be a complete ring around the whisker, so it can sense being deformed in ANY direction, not just one.
Given the enviroment you're using it in, I'm not sure how much current may be drained from the whisker, nor how it might affect corrosion if you plan on using it for an extended period.
Hope that helps,
Dave
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Johnny
Also, if you want to sense direction, you'd need atleast 2 contacts (one in front, one in back) both tied to different pins. If the whisker hit one, it would mean something pushed it one way... the other contact would be the opposite direction.
Dave
travel (in or out) of the conical entrance to the trap. The main problem is the complete water proofing of electrical components at the depth that the traps are to be set in.... The whisker has to be flexible enough to trigger a switch, or better yet mount a magnet on the whisker to trigger a reed switch or hall effect transistor, for easier waterproofing at depth/pressure you are going to encounter.
Bob
Bob
You haven't said where you're putting the traps (in a bay/inlet or ocean) but I'll assume it'll be bloody cold!
I don't know the temperatures you'll be dealing with.· But from previous google'ing, I've found that most batteries are rated at 80degF (27degC).
And they say you should subtract 0.028Volts per cell for each 10degF below 80.
This is from a paper I wrote for work.
Also, depending on the switch you use....you might want to epoxy the connections to prevent water from getting on them.· Hard to do when using some sort of microswitch (where water gets inside anyways.)
Not sure if things will short out on you, so far as exposed contacts go!
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Steve
http://members.rogers.com/steve.brady
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
If it is really cold, go with lithium batteries (not lithium-ion rechargables). You can get them in AAA and AA type at Walmart or anywhere nowdays, and they're slightly higher capacity than most alkaline cells. They work fine below freezing, which is probably several degrees below what you'll be encountering with a lobster trap. And you can discharge them a lot harder/faster.
Dave
The location of the traps most likely will in a·fairly well sheltered harbour to start off, and perhaps work our way outside more as we gain experience / better equipment. The water temperature is probably going to be in the 0 to 10 celcius range, and they will be used in the spring (to start off with).
About the issue with water shorting things out, I don't really understand how all of that works. I have seen divers, take underwater with them, 120v flood lights so they can see what they are doing. It was just a normal pig tail socket connected via a splice and some black tape to an extension cord. I don't understand why it a: wouldn't blow a fuse / trip breaker, and b: why they didn't get a serious electric shock... or worse.
The design I have come up with for the whisker will depend on not being sealed, if I don't have to seal things up, it would make things much easier. I'm going to need to do some experimentation. The design here will allow me to adjust the tension of the whisker so that we can avoid having false triggers, such as strong current / small fish swimming through etc.
let me know what ya think
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Johnny
Dave
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Johnny
http://people.deas.harvard.edu/~jones/es154/lectures/lecture_2/Ohm'sLaw/Ohm'sLaw.html
Although it's not nearly as conductive as copper, salt water could affect things.
Dave
NiCd are said to be rated to -40C (from BatteryFAQ).· They're cheaper than Li-ions but do have a higher 'self-discharge' rate...take about an hour to charge and have one of the higher cycle rates (discharge/charge/dishcharge).
Actually, just for other users' delights, I'll post the BatteryFAQ in the Sandbox for people's's future reference!
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Steve
http://members.rogers.com/steve.brady
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
Put a magnet on the 'whisker', such that when it is moved it comes close enough to the tube to trigger the contact. Then seal the contacts inside a water-tight container (a test-tube might work for this, or even PVC pipe).