On Mon, Jun 23, 2008 at 8:57 PM, Atte André Jensen <atte.jensen(a)gmail.com> wrote: There is a $1 device called a photoresistor that turns light levels into varying resistances. Putting it in serial with a low powered (ie watch) battery would give you an analog signal that varies with light level. Put lights behind the audience and their movement will change the light levels detected (most useful with multiple sensors (one audio channel for each, of course), and perhaps also gels, so they respond to particular colors of light. If you can destinguish between signal and ground leads on a cable, this is what the set of connections should look like: (you could alligator clip to a cable, or cut a cable where one end was busted, and solder onto the bare wires, or, of course, solder onto a regular old jack) ground --- battery minus battery plus --- photoresistor --- signal the housing is left as an exercise The next step, of course, is writing the software that interprets a slowly changing signal from an audio channel and influences the music. Make sure you do not monitor the signal from the photoresitor, the levels will be funky, and it will be extremely bass (most likely way below hearing threshold, well into plain old speaker coil frying territory). You will probably want to lowpass the signal as well, to get rid of crackle and line noise. Another idea that works with this is handing out flashlights (if the flashlights and sensors both have a variety of gel colors, different audience members have varying levels of influence on different parameters. With pd and gem, it is easy to bind parameters to color/light levels on particular webcam pixels (in fact I have done this before), but this will use vastly more cpu, and in the long term actually be more work than the idea described above (but it is worth considering if you cannot afford a $3 materials budget, or would have to buy a brand new soldering iron and solder that you would never use for another project). In my experience doing the webcam project, I found it most useful to use it in black and white mode, and have colored rectangles that can be clicked and dragged as overlays on the webcam display window, determining which parts of the camera's input control which parameters.