I've got a problem I want to solve on my bug list and my searches haven't brought up any answers. I've been using a Parallax pir (http://www.parallax.com/product/555-28027) to detect motion. They are very easy to use and very reliable so I can recommend them.
One thing I can't detect though is falling sheets of paper. One application I've been asked about is detecting when children drop wishes written on paper into a wishing well. The pir isn't sensitive enough to pick this up so I'm wondering if anyone has any ideas? Ideally I don't want to add anything to the paper to detect motion so using RFID etc won't really work, want I really want is an ultra sensitive motion sensor…
Thanks for any advice!