Depth sensor

Hi to this amazing community . I'm a Newbie who has the following project in mind . I thought it was easier, but I have no idea how to carry on . I'm a diver who wants to make a profundimeter to measure how deep I am . As I didn't find any depth sensor, I thought in using a pressure sensor. I had some ideas , like using a barometric sensor inside a sealed cilinder to measure the pressure of the air inside it, but then I realised that, if I put surface air, I will have always the same pressure . Sorry if it sounds silly . So I have no ideas .

I don't see how to solve it . If anyone could help me, I would thank it. Thanks in advance .

I'm guessing the cylinder wouldn't work as it's a rigid object, therefore not changing a lot according to the outside pressure. But maybe if the sensor is inside a rubber ball, for example, I'm guessing (although I don't have diving experience), that this way the outside pressure will infer on the pressure inside, therefore allowing to measure the change in pressure.

Just a thought... :)

Great idea . When you dive , as you go deeper, the preasures increases one Atm. each ten meters . If I put the sensor inside a rubber ball, it may work . I’ll give a try and comment the results . Byeee.

you could take a balloon in a cylinder(open at both ends). The cylinder protects the balloon and the electronics?

My idea is , as it is an original prototype , use a tupper Ware or something similar to the electronics , and put the barometer inside the balloon .The tupper and the ballon ( or the cilinder ) will be fastened , and electronics and balloon will be joined via wire. If the balloon crashes, the only components I would break is the barometer . I Will have to seal the tupper in a strong way .

You can get differential pressure sensors that have one end sealed at atmospheric pressure and the other end open. You can get versions that can stand liquids in the open end. Salt water is on of the liquids that can be used.

Thanks to everyone . I think I have found the solution here :

if you sink a glass in water, the water will penetrate the glass as the glass sinks, at a rate proportional to the volume of air contained in the cup and the water pressure. The higher the pressure, the more water enters. The air volume decreases as the pressure increases. The volume of air will be half when the pressure is doubled. Imagine a plastic tube, transparent, very thin, spiral wound, sealed at one end, filled with air. When you immerse the tube in the water, because it is very fine, but the air will not escape the pressure of the water will come gradually, while the tube sinks. If it rises, the air expel water. To sink, while the water is in the middle of the tube, the water pressure will be doubled. When reach two thirds of the tube is three times the pressure and so forth. The formula is:% of water filled tube = 100 - (100 / (1 + depth)). Depth in meters, pressure in atmospheres. Try.