Found in a Popular Electronics from the 90's, this circuit can generate frequencies according to the values of the employed components, according to the table next to the diagram.
This circuit was found in Electronics Handbook, Vol XIII 1993 and consists of a simple direction...
This circuit works only with carbon microphones, due its low impedance. The speaker should be good or...
This is the normal circuit of a relaxation oscillator using an unijunction transistor such as the...