Talking about my circuit again. Somehow I saw something about bypass capacitors on the supply pins. Would it do some good to implement them in my circuit ?
Every transistor circuit and IC must have a decoupling capacitor very close to the supply pins of the IC or circuit. Your TL081 opamps have some voltage gain as high as 3MHz so they need high frequency ceramic decoupling capacitors (47nF or 100nF) to prevent high frequency oscillation and your circuit probably needs low frequency 47uF or more electrolytic decoupling capacitors to smooth low frequencies.
Yesterday it looked like I made a major step forward in that sense that I saw sometimes no longer a peak bottom curve over a period of time but saw a longer peak curve. Looks like the simple LP filter I have using 100ηF capcacitor and a 100K resistor is working from time to time but on very selective vibrations of my working desk.
Today if I have time I will build a Sallen- Key LPF and integrate it into the circuit.
All the supply pins do have now a 47ηF capacitor. Somehow I got the impression the output looks better. Will keep you informed.
100k ohms feeding 100nF to ground makes a simple lowpass filter that is -3dB (0.707 times) at 16Hz. Its level is -12dB (0.25 times) at 64Hz so it noticeably reduces electrical interference and at the sensor resonance frequency of 75Hz it flattens the resonance.