The idea is to make a “parasite” on a finger. The “parasite”, as a ring, could opportunistically harvest small bit of energy form the movement of a finger. After a series of tests, the Piezo Element turned out to be a feasible material.
Test 1: Piezo Vibration Sensor (Large)
In my test, this Piezo Vibration Sensor could generate up to 0.212v itself, which is much more less than the data in its datasheet. (Datasheet)
Test 2: Piezo Element
This Piezo element could generate up to 2.39v in my test. The voltage is 10 times than the voltage generated by the Piezo Vibration Sensor.
Test 3: The Circuit
It’s a basic capacitor charging circuit. A 1N5226 diode (see below datasheet) is in series with the 1 uf capacitor. The forward voltage (at I = 200mA) is 1.1v. So only the round piezo element could be able to charge the capacitor. When pressed, the piezo element charge the capacitor; then presse the button to discharge the capacitor through the LED.
It did! The LED lighted!
I also would like to try other diodes with lower forward voltage.
Prototype
