This circuit uses a resonant reed relay to recognize the frequency of an input signal. Adaptations can be made to obtain functioning as a shield. The circuit is from 1965 documentation.
This circuit was found in an English magazine from 1979. The magazine no longer exists, but the...
This traditional TTL anti-clock setting was found in a 1993 American documentation. The circuit...
The astable multivibrator shown by the figure can produce signals in the 10 to 10 000 Hz band...