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 simple diode test appears at other points in this section. Or circuit can be adapted to use...
Found in Electronics Now magazine in an issue from the 90s, this circuit is different from the...
This circuit inverts the phase of an audio signal, maintaining its intensity. The transistors can...