The core for my ROV include the following:

1. Thrusters
2. Vision
3. Lights
4. Communications
5. Brain

But I also wanted to be able to add payloads. The core systems in the ROV are being mounted in the two pressurized tubes at the top of the ROV. This leaves the lower part of the ROV for payloads. The first payload will be the manipulator. But ... how best to communicate between payloads and the core? The traditional way to do this would be with a "bus" - a common set of wires and protocols to allow various devices to be attached without knowing what they are before hand. If this were a PC I might be tempted to use USB, but that's a bit heavyweight for the moment. For me, the obvious alternative is to use the I2C bus as a basis. This gives me a well supported communications system and it is implemented by many devices and sensors. But communications is only part of what I need. I also want to be able to provide power to these payloads. I'm planning on providing 3 voltages levels in the ROV - 3.3V, 5V and 12V - and passing these to the payloads too.

The photo above shows the bus connectors I've choses. These are IP68 rated with 8-cores. I'm using 2 cores for GND, 2 for 12V (the "mains") and one each for 3.3V, 5V, SCL and SDA. Each payload will have a male connector, while the core will provide a number of females.