This is a CAN interface, using an MCP2515 controller and an ADM3054 transceiver. The CAN transceiver is insulated from the controller and has its own voltage regulator. Input power can be anything between 6-25V DC and has reverse polarity protection.

Also, having separate power supplies not only protects the Raspi, but also solves the problem of interfacing a 5V transceiver with the 3.3V system.

The next part is getting the kernel drivers working. Not my thing really, I prefer soldering ;)