This oscillator for frequencies up to a few tens of kilohertz was found in a 1970s documentation. The transistor can be of general use. For the component values used, the frequency is 250 Hz.
This interesting capacitive water level sensor was found in Popular Electronics. The circuit can be...
LTC7841 PolyPhase® Synchronized Boost Controllers Mouser Announces Analog Devices LTC7841...
This circuit was fond in an old publication of the years 1950. The transistors are germanium types and...