This code key uses a PLL and an oscillator that generates two frequencies that must be recognized for the relay to be activated. The circuit is from an 80's Popular Electronics.
This traditional circuit with the 555 was found in a 1984 documentation. In this oscillator, the...
This circuit was obtained in a publication for radio amateurs of 1977. It is used to reduce the...
This LED indicator circuit uses an LM339 comparator. The circuit was found in the January 1995...