The Vehicle Interface (VI or CAN translator) is piece of hardware that connects to the car's CAN bus, translates proprietary CAN messages to the standard OpenXC message format and sends the output over USB, Bluetooth or Ethernet/WiFi to a host device.
The OBD-II port has one standard pin pair for a single CAN bus, but many automakers expose other buses on additional, non-standard pin pairs. For this documentation, we'll use this nomenclature:
|OBD-II Pin Pair||OpenXC Bus Name||Other common name|
|6 (+) and 14 (-)||CAN1||CAN high / CAN low from ISO 15765-4 and SAE-J2284|
|3 (+) and 11 (-)||CAN2-1||Ford secondary, Chrysler CCD|
|1 (+) and 8 (-)||CAN2-2||Ford: infotainment, GM: J2411|
Most vehicle data is available from CAN1, and all vehicle interfaces connect that bus. Some data is available only on CAN2-1 or CAN2-2, and these buses are not connected to all available VIs (see below). To find out if the information you need is on a bus connected by a particular VI, check the binary firmware documentation for your vehicle manufacturer.
There are two ways you can obtain a vehicle interface.
Build one yourself! The original OpenXC design was built on a chipKIT development board and is still fully supported. The design is open-source and posted below, along with instructions on how to assemble all the required parts.
The VI is a open source reference design for a "dongle" style vehicle interface that connects directly to the diagnostic port with no cable. Ford created this design and manufactured a small quantity to seed the developer community. If you have an idea for an OpenXC application and this hardware would help, submit a request to receive one of these prototypes.
The reference VI is not as compact as the C5, but it is open source hardware, so you are free to use or modify this design in your own hardware, and it connects to both the CAN1 and CAN2-1 bus pins (and with a small modification can connect to CAN2-2).
CrossChasm has graciously made the C5 available for purchase from their website, and contributed code to the VI firmware to support their platform. The device on the left is Bluetooth only. The devices on the right is 3G Modem only. Both devices have the exact same programming interfaces. See the vi-firmware documentation for more details on configuration options.
The C5 is a very compact interface, so it's great for fleet deployments. It connects to the CAN1 bus pins only with the default cable. A crossover cable is needed to access a secondary CAN bus.
This VI design was the first OpenXC interface, and is still fully supported by the latest VI firmware. The design uses entirely off-the-shelf components, built on top of a Digilent chipKIT Max32 development board (open source hardware!). The VI can be assembled with a range of functionality starting at around $110, with no soldering required.
The chipKIT VI can connect to up to 2 CAN buses simultaneously, and you can choose from any of CAN1, CAN2-1 or CAN2-2.
There are many possible implementations of a VI. The minimal functional requirements are that the VI:
Optionally, the VI may:
Unless you are implementing custom CAN messages, you will most likely need a pre-built OpenXC binary firmware from the manufacturer of your vehicle. Each OEM can decide whether or not to participate in OpenXC and if so, decide which types of data they wish to expose.
Once you've purchased or constructed a vehicle interface, you can get started with one of the programming environments to make sure it's working correctly. Both the Python and Android environments have a "smoke test" you can use without writing any code.