The circuit shown is from a 1994 National Semiconductor documentation and can be implemented with more modern operational amplifiers. The power supply must be symmetrical.
This is the circuit equivalent to the small key chains that were common in the 90s that emitted a...
This circuit was found in a Poptronics of the 90's. The components can be changed to the desired...
This circuit was obtained from a 1976 NASA handbook. The circuit makes use of an operational of the...