This circuit was found in a 1966 EEE. The circuit uses transistors from the time but can be made with modern equivalents. The operating frequency ranges from 0.1 to 1 kHz.
This simple oscillator with two general-purpose transistors has its frequency given by capacitor...
This flood or humidity alarm was found in an English publication in 1991. It can still be fitted...
We found this interesting configuration in a 1976 technical documentation. Equivalent diodes can...