Potential project: detecting lobsters in a trap

Hi all,

I'm investigating creating a device to detect if (and ideally how many, although this seems much more difficult) there are lobsters in a trap. The trap would be between 20-100 feet of saltwater, and potentially underwater for days at a time. The design I'm envisioning would involve a water proof container with motion / proximity sensors which would communicate via a thin wire to radio beacon attached to the floating buoy on the oceans surface. The buoy would then relay the information via radio waves to shore.

I'm very new to electrical engineering so I'm not sure where to begin. I could use help understanding the more difficult parts of the design, as well as types / brands of components to purchase and test with. I'd like to build a prototype for testing on land first with a simple Arduino - after this I'll likely seek out a more minimal circuit board if possible.

Thanks very much in advance,

Forrest

The buoy would then relay the information via radio waves to shore.

You could work on figuring this out first as it might be difficult.

I thought that might be the case. Any idea how difficult/type of equipment required is to transmit even a boolean value (on/off) several miles via radio waves (or another type of wave, but I'm guessing radio is best suited for this scenario).

I reckon the cost of making electronic equipment that can survive at sea would far out-weigh the value of the lobsters. It is hard to think of a harsher environment.

What about an underwater camera on the end of a long pole ?

...R

Could be a way to let others know i is time to raid your traps.

Robin2: I reckon the cost of making electronic equipment that can survive at sea would far out-weigh the value of the lobsters. It is hard to think of a harsher environment.

The critical word is "sealing".

There was a thread about crab traps a while back. crab trap monitor There may be information you can use.

Paul__B: The critical word is "sealing".

I think the more critical word is "HOW?" And (with all due respect to readers) I don't think there is any point in answering that unless you have actual experience of doing it successfully.

...R

There was a thread about crab traps a while back.

Same class assignment, perhaps?

Lobster season just opened somewhere.

Perhaps this is just a trawl

...R

One does try to claw back a bit of sanity ...

looks like with all the negative attitude and 'it can't be done' the OP went fishing elsewhere.

what strikes me as odd is that there are such a huge and vast array of unmanned submersibles and manned submersible. that scuba divers have been using electronical things underwater for decades.

a simple whisker on each entrance to count visitors. an ULF pulse might be possible, not sure if it is legal.

sealing is simple. at 100 feet, the device is under 4 atmospheres, or about 50 PSI. not hard to work with. if you use brass bolts with o-rings, you have an electrical connection through the case. with no fear of leaking.

look at scuba flashlights, tons of them rated for 200 feet. but as was noted, the 'ship to shore' communication would be the hard part.

https://www.youtube.com/watch?v=FE53y2-t6V0

http://hacknmod.com/hack/remote-control-pvc-submarine-with-onboard-camera/

The positive thing about this particular question was he's not trying to get wireless transmission of data through 200ft of water. At least that part seemed sensible and doable.

Scuba folk (and their equipment) do not stay underwater for months at a time, or in ocean storms.

How much is a scuba torch? How much does a fisherman get for a lobster ?

I have no doubt it could be done - but not at a price that could be justified by the price of lobsters.

...R

dave-in-nj: looks like with all the negative attitude and 'it can't be done' the OP went fishing elsewhere.

"fishing", get it? ;)

To be fair to the responders, I doubt many people on this forum (myself included) are experts at sealing Arduinos to operate under 200 feet of salt water for weeks at a time. One issue that springs to mind is simply: how to power it? And assuming that on the buoy you have a radio transmitter, it could be tempting for people to steal the transmitter (let alone the lobster).

Actually, it think this project is fairly doable if you have moderate construction skills and some money to burn.

The buoy would be a simple heavy duty pvc cylinder housing all the electronics and the battery. This means machine work would be involved. Access to a lathe is critical. The underwater sensor wires would be drawn trough thick a LDPE flexible tube. The buoy would be attached to the cage below trough a marine grade chain. The tube would be hence strapped to the chain.

The RF link...well, it depends how far your receiver is. I'd opt for a HF module if you're far away, or a UHF one if you're fairly close. A battery that lasts for months. Either stack those 26Ah lantern 6v batteries or go for li-po (if you're bold enough).

As for the trap. Obviously it must be weighted down, which is the easiest part. As for the sensor...this is tough. Mechanical parts in the sea tend to fail quite quickly. Marin life builds up very quickly on immersed stuff. I'd go for whiskers too. Whiskers with vibration sensors stuck in them. LDPE tubes with those simple mechanical vibration sensors. Make a whole array of these whiskers in the cage. If there was only one lobster in the cage, only a few sensors would trip. If there were more, then the whole array would light up.

You could put it at the entry hole, but i'm not sure the would trigger when the lobster entered. If the lobster moves slowly probably not. But i presume once they are trapped they tend to move a lot. So an array might be more suitable IMO.

Obviously the devil is in the details. But this project is doable in my humble opinion.

Robin2: Scuba folk (and their equipment) do not stay underwater for months at a time, or in ocean storms.

How much is a scuba torch? How much does a fisherman get for a lobster ?

I have no doubt it could be done - but not at a price that could be justified by the price of lobsters.

Well, I'd hazard a guess there is a sentimentalist hiding in there somewhere! But the following did come to mind: What is a cynic?

a man who knows the price of everything, and the value of nothing :P

1:1: What is a cynic?

a man who knows the price of everything, and the value of nothing :P

I'm not sure where you are coming from - but I was just suggesting a comparison between the value of a lobster and the cost of scuba torch.

If I turn on my sentimental switch I would say, leave the poor lobsters alone. I don't think humans should capture wild creatures for commercial purposes.

...R

Robin2: I don't think humans should capture wild creatures for commercial purposes.

...R

I would be happy to leave them alone. that is if they would be ever so kind as to just walk into my boiling pot..... oh, and be a sport and bring some butter.