will there be an ultrasound sender on the dock and a receiver on the cleaner unit? Or the other way round?
I think there are a few ways this can be done but there is one currently on the market called MOAI that utilises ultrasound.
I'd say both. To be able to navigate using ultrasound the mobile cleaner must answer, there must be a round trip, otherwise you don't have the distance but only the angle to the base station.
That means your final year project choose out of several possible way exactly the same way as a product already on the market? Why don't you try a different way? Just copying a device commercially available isn't innovative. Is it this what you learned in college?
Why not bring it to the next level.1) no need to disturb your fish with ultrasound (there just have to be species that can hear that).2) no need to program anything, chunk it in the tank and that's it (well, place it in the tank against the glass while attached to the base station - in a corner so it can be used as reference to find the base station).Then have your cleaner robot travel around the tank on it's own, measuring the dimensions as it goes, sensing where the gravel layer on the bottom is, sensing where things are attached to the glass that have to be circumnavigated. You may require it to be a rectangular tank, as curved surfaces make it a lot harder. Create a map and it plots a good course to cover all the glass, and when in need of some power return to the base station to top up (hence the corner: makes navigating easier, just remember the path to the corner navigating references such as other corners, the water level and the bottom level).Sounds simple enough but probably not going to be easy :-)