Something which has confused me for a while is the use of a piezo element as an analog sensor inputting to an Arduino analog pin. Schematics in this forum and generally around the Internet generally show the piezo sensor ground to Arduino ground, sensor positive to the analog pin, and a pull-down resistor (10K perhaps) between the analog pin and ground. I have no problem getting that to work. I can even put a resistor or pot in series (like 1M) to attenuate the signal (adjust the sensitivity). Works great.
But here's my confusion...piezos can generate very high voltages (when used as a knock sensor or a drum pad). Also, because they are AC devices, they have negative as well as positive voltages. How does one justify their use, in the manner above, when a signal to an analog pin should be between 0 and 5 volts only? Doesn't the excessive or negative voltage cause a problem? Or is perhaps the current so miniscule it doesn't cause a problem?
Thanks for your help in clarifying this for me!