I recently started a project to make a digital gauge cluster useing the OBD-II interface. The cable I bought (on ebay) connects via USB. However, it is nothing more than an emulated Serial port (COM port). So, to request and receive information from the car, I needed to communicate through the COM port. I'm not sure what language you plan on programming in, so your route may be a bit different than mine.(1) Were to find structured information about getting data from OBD-Interface? Plugin in the Interface, connecting a computer via USB/Seriel and then - how to get the first data?
These are the very basics:
(1.) to start communications, send "ATZ" to the port. It will respond by echoing back "ATZ" and the version of the chip you are using (in my case ELM v1.2)
(2.) to turn off echoing of your commands send "AT0" <--Thats A-T-Zero. It should reply with "OK" or something similar
(3.) To get information for a specific item, you send it's PID. You can get a list of PIDs from here: http://en.wikipedia.org/wiki/Table_of_OBD-II_Codes
(4.) After you send the PID it will respond with the requested information in the form of HEX values. You need to convert the Hex values to decimal values and then use the information from the "Formula" column in the PID table to calclulate your ending value.
(5.) Request the next piece of information to continue the program.
Those are the basic steps. If you need some source code in VB.net 2005, let me know. Its not complete, but it should give you an idea of how to get the information.
There used to be one called (I believe) Jelmulator. I haven't been able to find any working links to it though. If you find one, please let me know! It would be much easier than running out to my car to program!(2) Is there a car emulator for Windows PCs? So a program which acts like a car and sends the information to the usb or serial interface as a real car would do?
Good luck with your project!