how to use multiple(4) piezoelectric sensor to determine different pressure take
Pressure is better measured with pressure sensors made of velostat. Piezos create terrible voltages, which burn your sensitive circuits. Precisely what kind of mechanical action is it that you want to determine? Do you want to measure it or just detect it?
You can connect a piezo through a fullwave rectifier (4 diodes) to a BJT gate. The BJT charges a wire with no pulldown that goes to a digital pin in proportion to the piezo tap. The digital pin eats 1 uA per read, I made one that showed a very light touch taking 20 reads to change HIGH to LOW while a hard smack with a screwdriver butt took over 2000 reads.