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 obtained from Linear Technology documentation from the 90s. The circuit uses...
This circuit is from a 1967 General Electric SCR manual. The capacitors are polyester and the...
This circuit is from Motorola's 1990 Linear Databook. The transistors allow equivalents and the...