Issue with Analog Input being constant


I am trying to analyze (with the arduino uno analog inputs) Vout from my non-inverting op amp setup.

Basically, when a force is applied to the FSR this will change Vout and I have some code to convert this into a force in my sketch.

See below for my schematic.

The Problem:

When reading the analog inputs, the values are not constant (when I view them on the serial monitor). When I apply a certain weight on to the FSR the analog read keeps jumping between 280 and about 310.

However, when I check Vout using my multi-meter it is constant at about 1.4 V.

Is there a reason why the analogRead is jumping around so much? Would any hardware changes help this?


There is a mistake in that circuit, my mistake.

R9 and FSR should be switched.

You need to low-pass filter your signal. You should add 100nF between the non-inverting input and ground (to decouple your virtual ground) and a capacitor across R9 (ie between inverting input and opamp output if I understand right), whose value C will set the bandwidth in conjunction with R9 (the product of C and R9 is the time constant).