Help with charge amplifier circuit for piezo disk

[teslinius]

I have a project where i will use a piezo disk, after some online search i found that charge amplifier circuit is most suitable, i found it on this website https://www.allaboutcircuits.com/technical-articles/how-to-design-charge-amplifiers-piezoelectric-sensors/ but it doesn't mention what component value should be used except for Rin, what value should Cp(100pF?), Cf(10nF) and Rf(100k) be?



Best regards.

[TimFox]

C_f determines the gain of the amplifier in Volts/Coulomb (V/Q = 1/C).
R_f determines the low-frequency response of the amplifier and the decay time of the output from a pulsed charge.  Without it, the circuit would integrate its DC offset until the output hits one or the other limit of the amplifier.
I think C_p in your circuit is the actual capacitance of the piezo disc.
To get real component values, you need to specify these performance requirements on your circuit.

[Terry Bites]

Here's thorough guide. High Impedance Charge Output Sensors Sensor Signal Conditioning (part 3).pdf (484.85 kB - downloaded 221 times.)

[teslinius]

I want the piezo disk to detect when a object is moved, circuit will be supplied by a liion battery (3-4.2V), piezo capacitance is around 5 nF, i don't know if it's correct but i got Cf value around 8nF, what value should Rf have IS 100K ok?