[TZ] has been using ATtiny microcontrollers to read and pass along data from his Harley Davidson motorcycle. The image you see above is using an ATtiny 4313 to read data from the J1850 bus.
The J1850 protocol is an older standard which may not be available in newer vehicles. But if your vehicle has it, you may be able to tap into the bus through an ODB-II connector. [TZ] is decoding the data with the 4313, then using an inexpensive Bluetooth module to send the information to an Android tablet. Fortunately, someone has already written a nice GUI to display the speed and tachometer.
This isn’t the only approach to data harvesting with an ATtiny chip that he’s explored. There’s a second video after the break that shows a much more complicated setup. It still harvests the J1850 data in the same way, but also uses additional I2C sensors and an embedded ARM board to gather GPS data. Everything is pushed to his smart phone, which displays current gear, RPM, speed, engine temperature, fuel level, and GPS information via a WiFi connection.