This circuit was found in a 1967 US documentation. It shows how to build a gain control by digital signals. The circuit can be used as a shield. FET can be a modern equivalent.
This 1960s Signalite circuit uses two SCRs to achieve full wave control. The trigger elements are...
This shoot-to-target game uses well-known CMOS circuits and the player hits the LED by squeezing...
This TTL circuit can be used as a shield. The frequency can be changed by changing the capacitors. ...