“A piezo creates a varying voltage when you squeeze it. [We’ll] use it as a sensor by measuring the voltage the piezo produces across a 1 megaOhm resistor…Notice it has a very fast response, especially a sharp attack and decay when it’s knocked.”
This first test was changing the frequency as the piezo was scraped and touched.
And the audio version:
Piezo sample trigger (& speed)
Piezo sample scrub
And finally an example of an external speaker circuit. Will need to work on the output level for this.