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"In 1880, the Curie brothers found that quartz changed its dimensions when subjected to an electrical 
field and generated electrical charge when pressure was applied. Since that time, researchers have found 
piezoelectric properties in hundreds of ceramic and plastic materials. [...] Normal output voltages from 
piezoelectric sensors can vary from microvolts to hundreds of volts"


Piezo whack-300.png Piezo-pottery-fig 01.gif

Crystals Go to War 1943 Reeves Sound Laboratories; Piezoelectric Quartz Crystals for Radio


ledB #1


caption=LEDb workshop circuit

ledWorkshop01Zimmer - ledB

VOvbkyr.png gGJ4WlJ.jpg




HRgvpho.png UwN2K8dh.png


e8VP38K.png wxYIOdM.png




With a series resistor, you essentially use the internal ESD protection diodes for clamping. 
The resistor just acts as a current limiting resistor, albeit that 1 Meg is a bit on the safe
side. The resistor divider in the second picture has the same effect.
The first picture is really clamping it externally. The schematic however was made for a 5V
circuit (5.1V zener diode). You need to adjust it to 3.3V.
I do not know the resistance of your piezo, but assuming say 500 ohm, a 1uF capacitor 
would give a bandwidth of only 300 Hz. Depending on your piezo resistance you might want 
to lower this capacitor 1 or 2 decades. Furthermore, I personally would still put a series
resistor of say 10k between the first circuit and the teensy input. Just as a second layer
of protection towards the teensy. The clamping of the zener as a first layer. 
Than the internal esd diodes with the 10k resistor as a second layer
Edit: Or as Jp3141 said, a series resistor also protects when the teensy is off.

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