I have been recently trying to help Darren Curtis build a laser harp. He has run out of analog inputs on his mini to cv controller (he's got the same as i have). Since he only wants on/offs instead of analog voltages -> digital values, this got me to thinking about other (read cheap and quick) ways to handle more inputs in addition to the ones on his MIDI board.
I was at Cheap As Chips and found some five dollar usb mice. I picked up one in order to try it out with some LDRs replacing the buttons (etc) as perhaps suitable receivers for the lasers. At first the threshold point was a little too low (ie. ambient room light was triggering an on state). But I added a 100kΩ pot in order to have at least some control over the sensitivity of the device. It's a good start at least.
Yep. This is what I do on my days off.