Audio board line in piezo voltage question

[sorin_jay]

Hi, I have a piezoelectric disk that I want to use to pickup audio from a cello. However, the output voltage can get really high, and I don't want to burn out the teensy or audio shield. Recording on the multimeter, I got up to 9 volts, although that takes a running average so it could really be a lot higher. How do i connect that to the teensy?

A lot of the vibrations etc from the cello are low voltage (1 - 3 volts), but if something is loud I don't want to fry anything. What do I do? A voltage divider circuit (3300 and 2200 ohm resistor) doesn't preserve enough accuracy to get quality sound - just scratching and hitting it.

 

[PaulS]

Yes, you do need high voltage protection when connecting a piezo transducer.
This article gives you some more insight. The mentioned TVS diodes are very commonly used parts.

Paul

 

[MarkT]

Hi, I have a piezoelectric disk that I want to use to pickup audio from a cello. However, the output voltage can get really high, and I don't want to burn out the teensy or audio shield.

Piezoelectric crystals are current sources (strictly speaking charge sources), so you can just put a low value resistor across the output to reduce the output voltage. Without any load they drift a lot in DC value anyway so you should already have a load resistor in the circuit with luck - just try reducing its value. Adding something like 1k in series with the output is a very simple way to add a degree of protection (in conjuction with the standard CMOS input protection diodes). Alas increasing this protection resistor in value will increase noise on the audio signal so its a compromize.