This interesting sensor for RF signals was found in an article in the June 1989 Radio Electronics magazine. It is a field strength meter with an LED bargraph indicator.
This circuit indicates the polarity of a voltage applied to the input. The circuit can make use of...
Yes, tunnel diodes can also be used in voltage regulators, as shown in this circuit from a Radio...
This rather sophisticated circuit does not recognize false tones, such as harmonics, and can be...