I’m building a gear indicator and information display for my CBR500R. It uses an Arduino Pro Mini, Nokia 5110 display, and hooks in to the Honda diagnostic connector under the seat. Protocol is a custom OBD k-line format. Here is some useful information on the protocol used.
The first version I created used 2N7000 MOSFET’s for the serial interface and it worked fine on a breadboard. However, before I could build the final physical version I received some LIN transceivers that should simplify the circuit considerably. I’m working on a new version of the hardware design now.