I finally got around to finishing off this prototype 7-segment display module, based on the MAX7219 integrated circuit. I went for the largest displays that the IC can drive directly, but that meant wiring them all together. I've since acquired a slightly smaller 4-digit display which will be a lot easier to wire up. My home brew Arduino is,driving the module, but there are libraries in JAL for PICs for the MAX7219 as well as for the Arduino. The interface is a simple SPI type and could be driven from the Raspberry Pi except that the 3.3v/5v issue becomes a pain in the rear as usual. I'm keen to have this bad boy on the dashboard of the MR2 sometime soon.