This circuit was found in a 73 amateur radio magazine from the 90s. An LED extends the scale from 0 to 5 V to 10 to 15 V in this bargraph circuit. Other zener values can be used.
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...