I'm currently developing a HSI bar for the second generation Prius.
I'm using an Arduino microcontroller, CAN-bus shield, ODB cable and a 2x16 serial LCD display.
Here's a video of the first stage of development, basicaly like a scangauge, where it reads gas-pedal, brake-pedal, rpm, battery current and cooling liquid temperature.
(sorry the video is in portuguese)
Right now I'm developing the graphic display of the HSI bar using the limited 8 custom caracters with 5x8 pixels each.
I'll post more details about the algorithms later.