Proximity sensor?

[Andrew Schrock]

Hi all, 

I am currently building a multimedia sculpture (video/sound). It is DIY
related, actually, since it will have primitive mixing facilities, parts
of a casio sk-5, parts of a speak&spell, and an analog filter. However, I
know how to do all that.. my question today is: what do you think is the
best way to implement a proximity sensor? I was thinking some sort of IR
switch, but I've always had a bit of trouble with those being reliable. I
need it to turn the sound on when somebody walks in front of it and go off
when they walk away. Seems fairly simple, but it has to be rock-solid. Oh,
did I mention cheap? :) 

Also, if anybody has one of those old Apple IIGS monitors, please let me
know. (the REALLY SMALL green kind which takes composite video input) I 
need one, and the week I decided to go through with this project somebody
bought the one I had my eye on at the salvation army. Bugger! 

later
Andrew

-| Andrew Schrock | aschrock at cs.brandeis.edu |-