Found in American 90’s documentation, this circuit generates 300 Hz depending on the capacitors used. These components can be changed to obtain other frequencies.
With this circuit it is possible to use a common hair dryer as a hand dryer. The circuit is timed...
This circuit was obtained from an English magazine from 1979, but can be easily assembled today...
This circuit was obtained in a 1975 magazine, but it can be easily assembled using BC548...