Tell us about yourself!
Since you had to add the reinforcing plate anyway why not drill and thread a hole in that and cut that in half instead of the nut?
Your driver circuit design limits the diode current to 378 mA (1.25/3.3) which means the resistor would dissipate 472 mW (0.378 ^ 2 x 3.3 watts). A 2 watt resistor is a bit of overkill.
3D Printing Class
I suspect this will only work if you have some kind of notification sound enabled with enough energy to light the LED. For instance the Pop on my droid probably won't work.
Your circuit is missing a ground from the diodes' anodes on the left side of the bridge.Have you considered using some of the piezo-plastics that are available (see http://www.te.com/usa-en/products/sensors/piezo-film-sensors.html?tab=pgp-story for and example)
how about a complete materials list? What did you used for the Voltage Sensitive switch? What are the connections for the USB socket?