This digital circuit is from a Radio Electronics magazine from December 1991. It does not use a microcontroller, but rather discrete digital circuits of the time.
The frequency of this type is oscillator is given by the RC network. Calculations can be found in...
This configuration, which appears in other points of this section and website with small...
This circuit is from the 1960 Mullard transistor manual. The transistors are germanium from the...