This 1/2 hertz high selectivity filter was found in the December 1990 issue of Radio Electronics magazine. The source must be symmetrical. The capacitors can be changed for other frequencies.
This circuit can be used as a rhythmic light or as a control shield for incandescent lamps from...
We found this circuit in a European publication from the 1990s. Transistors are still common types...
Settings like this can be found in this section and on this website, but from different sources of...