This circuit was originally designed to measure capacitance with an ICL7107 but can be used with other digital modules. The circuit is from Electronics Now magazine from November 1996.
This preamp version uses BC109 transistors that are older versions of the current BC549 in plastic...
This circuit was found in a 1980s documentation, using a comparator from the time. The...
I found This circuit is in a documentation of transistors from 1958. It uses germanium PNP...