levardar:
The system is drawing 5mA current and I want to keep it down as possible, but the sound I need it louder, as I use it outside.
I tried with 74HC14 this:
Datei:PWM 8Bit MonoAmplifier Steckplatine.png – Hackerspace Ffmwith a speaker but my Arduino is not responding when is connected to breadboard of 74HC14.
Check your connections and try again. You can substitute your piezo for the speaker in that circuit, but in that case I suggest reducing the 100uF capacitor to 1uF ceramic, and connecting a 10K resistor in parallel with the piezo.