This 1967 Raytheon circuit uses a Raystor, an optical coupler with a lamp and an LDR. The circuit can be adapted to use another type of coupler.
The frequency of this oscillator depends on T, which for the audio band can be a common output...
This circuit can work with almost any JFET. The circuit is from an Electronics Now from April...
This voltage-controlled oscillator uses components that are still common in our market. The...