OBDuino is a device that connects to the OBD-II plug of your CAN enabled car, and displays various information about your car (RPM, speed, etc). It can also display custom information for 3 trips: the current trip which reset each time the engine is started, a user resettable general trip and the user resettable tank trip too.
Each trip can display average fuel consumption, quantity of fuel used, quantity of fuel wasted at idle (when speed is 0) and distance travelled. Remaining distance, calculated using the tank average and the tank size, can also be displayed.
It displays 4 pieces of information at a time and has 3 virtual displays so it can display up to 12 different pieces of data. Each display screen can be configured, as well as the use of the metric system (kilometers, liters, etc.) or the US imperial system (miles, gallons, etc.).
It also detects Diagnostic Trouble Codes (DTC) that turn on your Check Engine Light, as well as the pending DTC that were detected during last driving cycle, and provides the ability to clear these codes (fault ones only, by choice) when finished.
It detects the CAN speed and identification of your car the first time it is plugged in. When the engine is turned off, it shuts itself down after a few seconds and goes into sleep mode, until you turn the key back on. It can also be locked to the car, meaning if it's stolen it will not work on others cars.
Values of the various PIDs are outputed from the device and can be recorded with a serial port adapter (using a MAX232) on a laptop or directly on a SD card using a small daughterboard.
Active device consumes about 35mA. Eventually it will consume as little as 0.5mA in sleep mode (goal, will be tested with the all-in-one PCB final device).

ISO support

I released the ISO version of the OBDuino under GPL, it's hosted on the Google Code service site here: OBDuino.

CAN bus support

So far it has been tested on:
OK: 2007 Hyundai Elantra, 2009 Hyundai Sonata, 2008 Pontiac G5, 2008 Saturn Vue, 2008 Chevrolet Cobalt, 2006 Honda Civic, 2008 Dodge Caravan
Not OK: Jeep Patriot 2008, Honda Odyssey 2007, I will retest those soon

It is sometimes hard to know if your car supports CAN bus protocol or not, surfing the web I found information on:
2003+ Ford, Mazda, GM
2004+ Chrysler, Lexus, Toyota, Volvo
2005+ Audi, Mercedes
2006+ Honda, Saab, Mitsubishi, Volkswagen
2007+ BMW, Subaru, Hyundai
It may or not work if your car is 2007- but all 2008+ cars sold in North America shall support it.
For European market cars (Renault, Peugeot, Citroën, Fiat, Seat, Skoda, Alfa Romeo, Lancia, etc.) I have no information :-/

Hardware

see this page.

Configuration

see this page.

Logging and transparent mode functionalities

see this page.

Some Screenshots

Here is various screenshots of almost everything you can see on the screen.

Metric	Imperial
Instant cons: At idle so it displays per hour, when a certain speed is reached, display change to L/100
Average cons: The car has not moved yet so it displays the maximum, if it's less than 10.0 it will display 2 decimals e.g. 6.57	If it's greater than 99.9 it will remove the decimal e.g. 123
Screen 1:
Screen 2: When you change screen, the two lefts PIDs and description are showned for a second, followed by the 2 rigths ones. I didn't had time to shot the second one!
Screen 3:

Display configuration
Select yes or no to enter the config

Settings configuration

Screen configuration
	From screen 1 corner 1
Display toggles every second between the description and the value	To screen 3 corner 4

Others Screenshots

These are some screens I used at a time.

At startup

When the ignition key is turned to the ON position, device starts up and displays:

Instant fuel consumption, as the vehicle is stopped, the display is in litre per hour, and as the engine is not started it displays 0 litre per hour.
Average fuel consumption for the current tank.
Outside ambient temperature.
Average fuel consumption since the engine started, currently 0 as the engine is stopped. This is the "outing trip".

Time since engine started.
Engine coolant temperature.
Distance of the general trip.
Average fuel consumption of the general trip.

Average fuel consumption of the tank.
Calculated autonomy: distance you can do with the remaining fuel.
Fuel wasted at idle.
Fuel used in the tank.

While driving

Here is some screenshots of the device while driving:

Instant fuel consumption, as the speed is greater than a certain number, the display is in L/100.
Average fuel consumption for the current tank.
Outside ambient temperature.
Average fuel consumption since the engine started; it always starts high and your goal is to have the smallest number there :o)

Instant fuel consumption, as the speed is lower than a certain number, the display switches to L/h.
Average fuel consumption for the current tank.
Outside ambient temperature.
Average fuel consumption since the engine started; see the average got lower since I drove a few kilometres.

Instant fuel consumption.
Average fuel consumption for the current tank.
Outside ambient temperature.
Average fuel consumption since the engine started; see the average got even lower since I drove a few kilometres.

Before shutdown

Here is the three different screen before shutdown, compare with the three firsts above.