Found in the September 1972 issue of Radio Electronics magazine, this signal injector is based on the HEP580. The circuit is powered by two batteries and its frequency is basically given by C1.
Found with variations on this site, this circuit was taken from an American documentation from the...
This circuit generates damped sounds imitating a drum or other percussion instrument with...
This is the traditional configuration for a limit comparator or window comparator, using two...