This high-Q low-pass filter was found in the October 1990 issue of Radio Electronics magazine. The frequency depends on the capacitors used and is on the order of a few tens of hertz.
Found in an Elektor from the 90s, this circuit is based on components that are still common today....
This circuit was found in a Signetics documentation from the 1980s. Next to the figure are the...
This timer of 10, 25, 45 seconds and 5 minutes has its times selected by the keys. The circuit drives...