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 with transistors from a 1995 publication. The circuit is powered by a voltage taken...
This 1.5 A circuit has the output voltages adjusted by a selector switch. We found it in a Popular...
We found this different configuration that uses a fluorescent lamp as a negative resistance device...