This circuit was found in Radio Electronics from the 90s. It converts capacitance into frequency in order to obtain a proportional voltage that can be measured in a common multimeter.
This circuit uses a piezoelectric transducer to produce sounds like a buzzer. Frequency is...
This circuit was obtained in a 1978 publication, but it can be assembled with equivalent...
The input impedance of this circuit is very high, on the order of 4M ohm and the output impedance is...