[Arduino Uno] Underwater Detection of Crabs

Hello everyone!

I'm in my senior year at college, and I'm trying to work out some problems with my senior project.

Essentially, I'm constructing a rig in which a sonar sensor attached to a crab trap will monitor the entrance to said trap, and count the crabs as they enter. The data runs up a wire attached to a rope which connects to an:

-Arduino UNO
-Redbear BLE Shield

to transmit the data to an iPhone app I've developed. The issue I'm having is that I cheaped out and bought 2 of these lousy Transducers meant for air : http://www. eBay.com/itm/Ultrasonic-Module-Distance-Measuring-Transducer-Sensor-Waterproof-DC-5V-Voltage-/231458217811

Is it worth buying a harbor freight fish finder, or should I consider another option? Sonar seems like the best bet, I just didn't realize how hard/impossible it would be to get a transducer designed for air to work underwater. The range I need is very small (1 foot or so) so I'm not sure if that will be a problem.

In my exhaustive research saw talk of infrared sensors, but in salt water I don't expect good results.

Thanks a lot, any input is appreciated!


Hi, welcome to the forum.

I don’t know how you made that link, but this is a link : http://www.ebay.com/itm/231458217811
Waterproof Ultrasonic sensors are for cars in the bumper for park assist.

There are submersible ultrasonic transducers up to a certain depth. What depth are they at ?

I don’t know what to use to detect crabs. Some people work on a ROV, they should know more.

Fishing trawlers use more and more electronics. To detect fish at close range (in the net or at the entrance of the net) I think they use sonar, not ultrasound.

I'd totally go with infer-red sensors. Build your circuit, debug it, then pot the entire thing in "ice clear" Urethane. Crabs saunter by, break the beam and get counted. I'm betting you'll need more than one beam as they may try to back out on you..

Good luck! Sounds like a fun project!

-jim lee

Interesting!! Never thought infrared would work. I got a sonar sensor that I think will work, testing today

Infrared will probably not work as it does not penetrate in water very well at all.

The sonar I'm using (harbor freight) isn't doing anything... I got it hooked up to a 6 volt power source, and the lead set up to an analog pin. It doesn't seem to do anything... what could I be doing wrong??

Datasheet on the sonar you are using? What sort of signal is on the lead?