This circuit recognizes a tone determined by the tuned input circuit (R3 / R4 / C2). The circuit was found in Radio Electronics from the 90s. The 4046 is not a common component today.
This circuit turns on your car's backlight when a vehicle coming from behind gets too close to it...
This circuit from the 90s, was found in an Electronic Design of the time. The components used are...
We found this circuit in documentation from Ferranti from 1968. The circuit uses transistors from that...