We found this circuit in the Radio Electronics Handbook magazine special edition of 1992. The circuit uses an optocoupler as an electronic potentiometer.
This circuit, which presents a certain danger and should be used with caution, was found in the...
This circuit with variable capacitance diode (varicap) is from a publication from the 90s. The...
This circuit, shown in the figure, consists of a variable gain amplifier with differential input...