Piezo input stage for drum triggering

[luna5]

I want to design an input stage for my DIY midi-drum-trigger.

Piezo-Elements are used as drum trigger and i want to read out the voltage spikes with the built-in ADC of a ATMega168p in order to generate MIDI-Signals. I checked different resources for how to design a input stage for the piezos, since they generate a very high voltage, but the circuits i found are very different.

Here is a circuit i found:

I am very new to electronics, but this is how i would explain the circuit: The potentiometer acts as a voltage divider and scales down the signal. The BAT85-Diode removes the negative portion of the signal. I don't know what the resistor in parallel to the BAT85-Diode is good for. At the output of the opamp, there is a peak-detector circuit to hold the signal-peaks for a specific time and the whole signal is amplified by two (non-inverting-amplifier). Please correct me if i'm wrong.

So here are my questions:

• Do i have to add a buffer behind the peak-detector circuit when working with piezos or can i connect the peak-detector-output directly to the ADC?
  
• And if i have to add a buffer: I want to multiplex many piezo-signals with a HCT4051. It is possible to add one buffer at the output of the HCT4051 or do i have to buffer every eight signals before they go in to the Multiplexer ?
  
• I want to drive the opamps (LM324N) from 0 to 5V, and not from 0 to 8V like the circuit above. Is there anything i should change, when using this circuit ?
  

Thank you !

 

[nice keetee]

Triggers are inexpensive? Me forget how to read schematics anyway