I am using a non-inverting op-amp circuit (shown below) to linearize the output of multiple analogue force sensors. This is the circuit recommended by the manufacturer in their electrical integration document.The circuit is working and I am able Toggle between sensors by driving GPIO low for active sensors and high impedance for disabled sensors. However I have observed a larger amount of noise and oscillation in the output of the opamp when I apply force to the sensor with my bare hands. This noise is almost negligible when I apply force to the sensor whist covering the sensor with an insulative material.
I have found by increasing the capacitance of C1 to from 47pF to 1uF I have been able to eliminate the noise and oscillation. (Why is this?) however this is at the cost of having to increase the time between sensor readings to the point where it is not feasible for my application. The reason I must wait between sensor readings is the large capacitor will hold the voltage of the previous sensor for some time when I toggle between sensors.I have the following questions:
- What is the likey cause of the noise/oscillation (image show below)
- How can I eliminate this noise?
- What is the purpose of C1 and why does increasing C1 remove the noise/oscillation.