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 is from a 1991 publication, but it can be assembled with more modern components. We...
Found in National Semiconductor documentation from the 90's, this circuit has an output current of...
This circuit was obtained in a June 1987 magazine Hands-On. It is a circuit that indicates on an...