Found in a 90s Popular Electronics, this circuit triggers a load from the audio signal applied to its input. The controlled load depends on the MOSFET.
The circuit shown in the figure below is suggested by ON Semiconductor (www.onsemi.com), based on...
This circuit was found in an Electronics Now from the 90's. The integrated regulator circuit and...
This circuit for several frequencies was obtained in an American documentation from the 90s. The...