Hardware files for our university semi-autonomous submarine robot's motherboard design for the MATE ROV Robotics Competition (a submersible remotely operated submarine vehicle competition). This motherboard connects the surface computer to the main data-handler and general computer for our robot: a Raspberry Pi Compute Module 4. It serves as a module to control the thrusters and cameras on our robot.
We chose this device as our main computer because of its high-speed operation and inclusion of many desirable features, namely the support of a PCIe x1 lane. We used this PCIe lane to provide four high-speed USB 3.0 connections, which were used for our cameras. Other than PCIe, our motherboard has Ethernet, which is used to talk with the surface computer, back-up serial connectors, and expansion slots that are used to connect to our daughterboards.
Motherboard is a 6 layer board. The full system schematic located in "Motherboard System Schematic" and PCB located in "Motherboard_PCB". We have a Top Layer (1) and Bottom Layer (2) for essential routing connection. Next, we have (3) 3.3V layer dedicated to supply 3.3V and a (4) layer for GND GND Plane. Finally, we have a Horizontal Layer (5) and Vertical Layer (6) reserved for the low priority routing connections, such as a GPIO breakout headers.
We use a 12V and 5V external power supply (J9 Pg 1) to power the Motherboard. A buck converter takes the 12V power supply and switches it down to 3.3V. This 3.3V supply directly feeds the (1) external I/O board modules (slotted into Card-Edge Sockets) and (2) PCIe connector. The RPi CM4 and PiHawk external module uses the 5V from the external source.
The motherboard allows us to access the cameras underwater. The cameras are connected to an external PCIe-USB Exansion card. The motherboard uses a PCIe connector (J10 Pg 3) to convert the PCIe-USB Expansion card to command the RPI CM4 (MOD1B Pg 5) over PCIe. The RPi CM4 then uses ethernet (J13) to communicate to an external surface computer.
The motherboard controls our robot's thrusters. Our surface computer commands the RPi CM4 (MOD1B Pg 5). The RPiCM4 then communicates over USB.20 to a High-Speed-USB-Signal Switch (U8 Pg 6), converting the signal into USB Type-B Micro. This command gets sent to an external module (called PiHawk) that directly drive the thrusters. PiHawk is slotted into one of the motherboard's Card-Edge-Sockets (J8 Pg 2). In addition, to USB 2.0, it also communicates over UART to PiHawk.
The motherboard communicates over I2C to our I/O Board that our external, slotted into the Card-Edge-Sockets (J3 + J6 Pg 2). They are responsible for controling LEDs, Solenoids, and brushed motor controllers.
