I have a capacitive sensor connected to a 555 timer wired as an astable multivibrator and the free running frequency is 60kHz. When the capacitance of the sensor changes, the frequency of the 555 also changes. The maximum frequency deviation from the center frequency is 20kHz, i.e lowest frequency (60kHz-20kHz) is 40kHz and I want to convert this frequency deviation to voltage. I need a simple circuit using a 555, OPAMP, transistor etc.
I would prefer not to use the LM331 frequency to voltage converter.