Here is the lowest section of my submarine, with this being a temporary project to test different forms of ballast tanks mainly; compressed air ballast tank, Kevlar bladder syringe, and chemically produce a non flammable gas.

There are two solenoid valves the second facing you with the red dot and the first just to the right facing away from you. These valves receive air from the compressed tank. The second solenoid valve releases compressed air into the ballast tank and the first discharges air from the ballast tank. Opening and closing the valves in the right sequence will add or remove air from the ballast tank, thus changing the average density of the submersible. 

There are also two sensors in this picture. A pressure sensor just to the left of the second solenoid. It reads the pressure being released from the compressed air tank. The other sensor is hard to see in this picture, it is by this right and lowest part of the structure. There is a smaller red strip, this is to sense the presence of water. 

In the later test there will be a nether solenoid valve to add an release air from the pressure hull. In the case of water being detected this additional solenoid valve will release air into the pressure hull, hence creating a higher pressure in the hull reversing the flow, at least minimizing or prohibiting the invasion of water. 

In the case of a flood this section is unlikely to be damaged, one of the reasons it is the lowest part, and another reason to maximize the distance between the solenoid valves and my microcontroller, which received interference.

This section directly above the last has a grounded metal plates with two power strips attached, positive and negative. The negative is connected to chassis ground. Directly preceding are the two nickel metal hydride batteries in series in order to create a potential of ~15 V, in the event of a short-circuit there currently a 7 amp fuse . Above the batteries is a circuit box containing a four channel solid-state relay. I will show how about that in a later post.

In a nether addition I will be running with a different battery, higher voltage and higher amp year. I will have a 24, and 12 v regulator and booster.

This is the most open and least developed section of the sub. In mid-view there is a variable pressure regulator. I do not know of an affordable electronic pressure regulator so I have a mechanical regulator which uses an Allen wrench. It is likely I will use a stepper motor with a series of gears in order to change pressure according to death. It will also serve as an emergency override, this regulator can range from 0 to 750 psi.

To the left of the previousley discussed variable regulator is the pressurized air tank which runs at 4500 psi by an internal regulator this is neck down to 700 psi.

Directly above the compressed air tank you see my computer housing, this will not be discussed in detail here. All I will say for now, a UDOO microcontroller is partially encapsulated by a 3-D printed shell. The shell is open on the bottom to allow ventilation, in the case of the flood will be protected by the shell and the bubble held within.

The gizmos and gadgets you see are not in place. They will be held in the small void above the computer case there will be two protrusions that will leave the top of the sub, to fill and empty the ballast tank. Later on there will be a third which will allow a liar several terminals for more sensors. For now my external pressure gauge will be a inside reading pressure outside which is the black knob you see on the bottom of this picture. The pressure in these types will be equal to the external pressure is allowing me to read the external pressure from the inside with the exception for the brief moments when I am filling and releasing the ballast tank.

I have been quite vague and most of this post, I will be happy to answer any questions.