This circuit was found in an 80's Electronic Engineering. The circuit uses a multivibrator with neon lamps and an optical coupling system.
Varicap or varactor is the basic component used in this circuit of an American 80's documentation. The...
This circuit was obtained from the October 1977 Radio Electronics magazine. The meter is analog, and...
This circuit doesn't use CMOS functions, but instead a bipolar transistor. The main feature for...