This noise generator for the audio band was found in a British publication from the 1970s. The circuit can be implemented with modern equivalent transistors.
The frequency of the sound emitted by this circuit depends on the light intensity on the sensor....
This circuit is from a thyristor manual from On Semiconductor. It makes use of a PUT and a SCR...
This circuit uses only one NC75Z04 port from ON Semiconductor, but it can be implemented with...