Automotive diagnostics have come a long way since the “idiot lights” of the 1980s. The current version of the on-board diagnostics (OBD) protocol provides real time data as well as fault diagnostics, thanks to the numerous sensors connected to the data network in the modern vehicle. While the hardware interface is fairly standardized now, manufacturers use one of several different standards to encode the data. [Alex Sidorenko] has built an open source OBD-II Adapter which provides a serial interface using the ELM327 command set and supports all OBD-II standards.
The hardware is built around the LPC1517 Cortex-M3 microprocessor and can accept a couple of different versions. Here’s the PDF schematic, and a set of Gerber files (ZIP archive) for the PCB layout, if you’d like to dig in to it’s internals. The MC33660 ISO K Line Serial Link Interface device is used to provide bi-directional half-duplex communication interface with the micro-controller. Also included is the TJF1051, a high-speed CAN transceiver that provides an interface between the micro controller and the physical two-wire CAN lines on the ODB-II connector. The serial output from the adapter board is connected to a computer using a serial to USB adapter.
The software is written in C++ for the LPCXpresso IDE – a GNU tool chain for ARM Cortex-M processors, but can also be compiled using a couple of other toolchains. He’s got instructions if you’d like to build the firmware from source, or if you’d like to program the adapter via Flash Magic.
We featured [Alex]’s inexpensive PIC based ODB-II interface way back in 2007, so he’s been working on this for a while and has a good grip on what he’s doing.