capacitance to voltage conversion
There are a number possible approaches.

Use the fact that impedance at a fixed frequency varies inversely with capacitance.  You basically make a resistance meter, but with AC.  You put in a signal at known voltage and frequency, then measure the voltage of what you get out.

Use the fact that a capacitor together with a inductor define a frequency.  Use the capacitor under test with a known inductor as the frequency-setting part of a oscillator, then measure the frequency.

Dump a fixed charge on the cap and measure voltage.

Charge the cap to a fixed voltage, then discharge thru a known resistor and measure how long it takes to get to a known point on the discharge curve, like 2/3 discharged for example.

Use a known capacitor to see how the two share voltage after being connected with one charged and the other discharged.

Set up a camera with a machine vision system feeding optical character recognition and read the label on the cap.

Use your own brain and get creative.