This circuit uses a parallel resonant crystal to control the frequency. The circuit is from Radio Electronics magazine, February 1993. Equivalent transistors can be used.
We found this circuit very simple in an old documentation. The relay is high voltage sensitive, but...
This circuit was found in an Elektor from the 90s. The circuit uses common components even today,...
The circuit, shown in figure 2, is a monostable multivibrator with two NAND ports out of the 4...