Water deepth measure sensor for Fishing boat

Hi guys!

I want to build an water deepth measure device. I often fishing from a boat, and i want to know what deep the water is behind us. I want to measure from min. 1-2m to max. 10-20m.

There is a lot of sonar like THIS, that promise range of depth readout from 0.7 meters up to 100 meters thats perfect to me!

But what kind of sonar/transudecer its used by? I don't want to simply buy and use this, i want own designed device, I want to build it, decode by arduino, and display on Bluetooth...

Can you help me?

The obvious answer is to buy the device you linked to. Test it. IF it works to your needs, begin to disassemble it and learn what it uses and how the parts are used and then build you own device.

You will never learn how something works until you take it apart and put it back to gather.

Paul

Submersible devices are hard to build , the transducer itself has to get the sound into the water and thus requires the right sort of interface - a waterproofed cheapo sensor for example just won’t work

I have one of the “fish finders” linked in the OP (US$25 on eBay) and it works quite well. The sonar driver provides 200VAC at 200 kHz, so the batteries don’t last very long.

It is almost impossible for a hobbyist to make one that works as well, as (a) the design information is simply not available, (b) many of the parts are specialized and (c) the parts that are available, like the transducer, cost more than the finished product.

Acoustic properties of materials aren't that impossible to find, since you only need the
bulk/shear/elastic modului and density to determine the speed of sound and acoustic impedance.

All the maths for RF signals propagating down transmission lines directly translates to
acoustic or optical signal flow, this is basic physics of waves, not something obscure.

So a lot of the design information is available - something that might be hard to find
is the loss tangent v. frequency for softer materials like polymers, and its dodgy to
extrapolate from audible frequencies to ultrasound for these.

The basic bottom line is try to match the acoustic impedances of all the materials to
reduce reflection, and just like an anti-reflection coating for optics if you can use 1/4 wavelength
interface shims of intermediate impedance to join two unmatched materials.