This circuit was obtained from HAM Radio magazine in an 80's issue. The FETs are types of the time and the frequency is determined by the crystal. The circuit operates at voltages from 3 to 9 V.
This circuit, found in an American publication from the 1970s, produces an audible tone in a...
This circuit was found in a 2006 publication. It can serve as the basis for a microcontrolled...
By adding a transistor to the output and some polarization features we can obtain a higher output...