Using a 4046 PLL this circuit recognizes a 1.6 to 1.8 kHz tone by driving an output LED. The circuit is from a Radio Electronics from December 1989.
This circuit was found in a Popular Electronics of the 1990s. The sensor is a rotating mechanical...
With this circuit it is possible to obtain an intermediate voltage of 6 V from a 12 V battery with...
Found in a 303 Circuits from the 90s, this circuit converts signals from the 10 kHz to 150 kHz...