Found in a 90's EDN this circuit can be used as a shield. The transistor is a general-purpose type and the frequency of the emitted sound is determined by R1 / C1.
This circuit was found in a 1968 General Electric documentation. It has an input impedance of 2 M ohms...
This protection circuit was obtained in a 1969 Electronic Design. The SCR can be the current...
This circuit was found on an old EDN and can be used as a shield. Optical couplers are from the...