For my homework I made up some prototype circuits for "light chimes"...
I tested out the following methods:
- reed switch
- piezo vibration sensor
- IR reflectance sensor
- LED-as-sensor

Of these, the reed switch wins on cost and simplicity, which is probably
the reason why the artist in the video went that route.
We'd be looking at ~$1/strand or less in electronic components.

There's an open question of how to position the magnets in relation to
the reed switches. I'm guessing from the making-of video, those dowels
they're hammering through the board are steel rods with a permanent
magnet at the end, and they put the reed switches near the top of the
light string.
However, I was imagining small magnets affixed above or below the reed
switch on the string in an alternating fashion, so that as they swing
one would trigger the next. (Could be a metaphor for interaction between
people in society? Oops, there I go getting conceptual again...)  We
would want to make a small prototype to see how this actually works in
practice.

Then there's the question of how to enclose the dangling LED in a
touch-friendly way. I can't tell from the video whether the "chimes" are
a flat band of translucent material, or some sort of translucent cone or
rod? Where would we obtain something like that in bulk?

Of the other method, the piezo sensor gave a very natural flicker, but
the sensors are around $1.60 each in lots of 100, and the circuit
requires an additional pair of transistors. IR was costlier still and
required more components.
The idea that LEDs can be sensors as well as emitters has great appeal
in that it is still a novel concept, and it would be the cheapest route.
However, I'm not sure an Arduino can handle the work of scanning a 8x8
sensor matrix while drawing to it at the same time and have it look
natural.  I'm going to continue researching this.

Sorry I can't make it tonight. Let me know if you have any questions!

Tim

On 12/11/2011 10:34 PM, Georgia wrote: