Using a Parallax Propeller microcontroller to control an OBD interface via RS232, the results of diagnostic tests and live engine data can be displayed on an LCD display. By writing data to a 2GB SD card, data is available for analysis, as per the chart below. Don’t forget - this is in 32 kB of memory.
A Parallax Propeller Protoboard was used to validate the initial design.
The box ended up like that to the left. The ELM327 to serial box talks to the car and the lash-up in the project box works on the data from that. A VGA output is used to present data to a monitor if required.
In addition to engine data, the box can display/record acceleration data.
The data recorded provided all aorts of opportunities for charts and plots.