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.
This circuit is from an Electronics World of 1967. The circuit slows down the activation of a...
This metal detector circuit uses an AM radio as an indicator. The radio is placed off-station and tuned...
In the figure we have a sensor circuit that makes use of common transistors and a photo diode as...