This circuit was described in an article in the February 1993 Radio Electronics magazine. The frequency depends on the crystal and L1 is optional.
This circuit was obtained from an American 80's documentation. It can be implemented with modern...
We give in the figure a different application of 4013, which can also be used as monostable. In common...
We found this adapter in a 1970s American documentation on instrumentation. It is suitable for analog...