It is possible to use ARC/ez-bv4 under water but you would have to embed the whole system inside the robotic fish or ROV. The ez-b and small form factor PC would still connect via WiFi but it would all be done inside the under water robot. The system would have to be fully autonomous, unless you can find some way to use low frequency radio waves or infrared light to control the under water bot from the surface or outside the tank.

Another way would be to use an ez-bv3 with a tethered serial connection to the computer on the surface, but it sounds like you'd like a wireless solution.

We do have a wired ez-bv4 top board on the list, that could also potentially be used, but that's a future development.

@Jeremie , Thankyou

I see, course it can work if i using mini pc in the robot fish. 

Jeremie, is there a place to solder a wifi antennae? Perhaps a snorkal kind of arrangement with a floating antennae could be used.

Alan

Naw sorry Alan, there isn't.

There is a wifi-module from the same manufacturer that has a ufl connector for external antennas but it would be pretty painful to replace the wifi module on the ez-b for another.

Eric, how many servos and sensors and thinga are on the fish? Maybe something like an Arduino on board, acting as a slave to an EZ-B on the surface connected by a 3 wire tether to one of the UARTs.

I know you are on a pretty tight budget, so an embedded computer is probably not an option, but maybe a cheap used Android phone running ARC Mobile. You could have ot be mostly autonomous, and just connect some fishing line to retrieve it if it goes out of control.

Alan

@Alan in the fish is 5servo and 1 motor dc gearbox. Maybe i will use a android for connect to ez-board. I must making more space safety box in the robofish body.

Thankyou Alan

Nice work Eric.... Another excellent build by you....