In chat tonight, I asked for ideas for new display elements or functionality. A couple of ideas were: A donation box that played a short audio file (mp3) each time coins were dropped in the slot. This is certainly doable. A small mp3 module with SD card storage, opto trigger input (from the coin slot) and a small (1W) amplifier would be easy enough and not too expensive. I already have a supply of economical mp3 playback modules. The other one that stuck out was lights that followed a person as they walked around the display (or fence line). This could perhaps be done with cheap PIR sensors (maybe these) that either triggered their own local light output, or perhaps fed back into the show control PC for more elaborate processing. So, I'd like to hear people's thoughts on these ideas. Do they sound useful, desirable, practical, etc? Do you have other ideas for making a display interactive without blowing the budget completely?