After buying a new car that didn't have a trip computer to display fuel consumption statistics, open hardware hub member "winneymj" decided to make their own version based around an Arduino-compatible circuit. This is possible with some vehicles that have what is known as a CAN-BUS connector. The CAN-BUS is an automotive data bus that carries information between various devices in vehicle, such as the engine management computer, door locks, HVAC and so on.
By accessing the diagnostic connector in some vehicles you can make your own transceiver to interrogate the bus for data, and the designer of this system has done that to get fuel consumption data, and then used the Arduino circuit to analyse and display it on a nifty home-made display as shown below:
Finally if you're going to fit this type of project to a car that receives dealer servicing, it might be a good idea to remove it before the visit to the dealer! Nevertheless the project may seem a little complex. however the required code, design files and notes have been provided on the project page. And for more, we're on twitter and Google+, so follow us for news and product updates as well.