After looking at some of the control boards for 3D printers, I was inspired to build a carrier board for solenoid switches. The idea was put 3 Pololu RC switch boards on the carrier board, along with 12 volt regulator that would supply the required solenoid power from a 6 volt source. The advantage of the carrier board is that keeps everything compact, eliminates a lot wires, and allows for quick swapping of the components if one should fail. Additionally, I added a slightly bigger switch board to run the pump from the same board. Here's the prototype board and the components. The boards (from left to right) are the Pololu R/C switch with Medium FET (good for ~ 15 amps), 12V regulator (2-12v input), and R/C switch with small FET (good for ~3 amps). All of the switch boards allow you to program the direction and position that the switch activates. Two of the small boards are connected to the same input from the receiver, one activating in the forward direction, while the other activates in the reverse direction. Here's the assembled board. The total cost of all the components is around $30. The terminals could be replaced with connectors, but I wanted to have something that I could easily swap into any ship. The carrier boards and Pololu boards are coated separately with two coats of liquid electrical tape. The unit has successfully passed full operational tests while under water.
The circuit is simple enough that the carrier board can be made from perf board. If you don't want the pump control on the board, everything to the left of the dashed line can be eliminated.
