Then as soon as I switched to battery power it stopped working. It took me a while to figure out why, ie. until then I'd always had a USB cable connected to the device and my PC was forming part of the system.The difference in capacitance was easy to measure when it's on USB - it can actually detect a hand from a few inches away. Without the USB cable the difference drops to almost nothing. I had to go from 1MHz to 8Mhz clock to be able to measure it.
A piece of foil in the base of the jar works.
Check out 'butteryfly in a jar' at youtube. I'm 99% convinced it's a piezo. One guy writes 'spoiler alert - see how it works.' He plays with the butterfly, opens the lid, and shows where the batteies and switch are. And that's it. He shows how it OPERATES but not how it WORKS. So that's yet another 2:43 of my life waste that I'll never get back. Another forum there's a buncha discussion the butterfly, capacitance, piezo, and the thread ends where someone writes 'I'll take one apart and let you know.' That was in 2011. [checking sundial [sigh]]Given $ vs ease of design, piezo is cheap, easy and reliable.
QuoteA piece of foil in the base of the jar works.What if the foil was replaced with transparent conductive spray?
Any new progress?