This circuit was found in documentation from the 80s. The components are from the time, but the configuration can be adapted to use modern components.
In this circuit of a 1991 publication, we can use the 2N2646 unijunction transistor and the sensor...
Measuring capacitances and resistance this simple instrument was found in Radio Electronics...
Found in a 90’s 303 Circuits, this circuit uses components that are still common and has a common...