I want to build a homebrew keyboard guide lights system

This is what I want for my digital piano. (Also suitable for acoustic piano, organ, etc.)

A strip of LEDs along the keyboard, one for each note. A software program in the PC (or Mac or Linux box) that sends commands via RS-232 to the strip's interface (probably using a PIC microcontroller). The commands sent to the strip switch one or more LEDs on or off. A minimum of any ten LEDs on at any one time is a requirement.

Now I could do this with a MIDI decoder board, but they are not cheap. A homebrew device would be only pennies in comparison. Also, the MIDI decoder boards have to run much more involved embedded software to filter Note On/Messages, check running status etc. I don't need any of that. I merely need the simplest system possible to send a byte to the strip and have it interpret the appropriate LED. One byte would suffice for 0 - 127, plus a bit for on or off. But I don't even envisage covering the full keyboard range. Just 5 octaves would be more than enough. Even four for starters. I'm not even considering USB, since RS-232 would be more than adequate and is far simpler.

But before I continue I want to know whether anyone else has already done it. I don't want to reinvent the wheel! So I'm looking for schematics, documentation, pictures, anything, really. Even ideas that someone has started and not got round to finishing! I may even avoid using a microcontroller at all and just use an old 6402 UART and a few 74... latches and stuff.

Some years ago Harmony Central produced a brief review of the Piano Wand that they had seen at NAMM '99, but there is no mention of this product anywhere else on the internet.

I have not done it but a friend just picked up a children's keyboard at a thrift shop for $2 that does it. Clear keys, but only the whites light.