This audio level indicator was found in October 1980 Radio Electronics magazine. See the table with the dB values of the indicated signals.
This circuit for vehicular use is from an 80's American publication. The circuit has a light...
You can change the output voltage of a fixed 3-terminal regulator using a zener diode. The voltage of...
This circuit was found on a Radio Elettronica (Italy) from April 1974. The circuit can still be...