We found this circuit in the 1989 Radio Electronics Experimenter. The circuit uses common components, and the thermistor is supposed to determine the value of the trim potentiometer.
Found in an American publication from the 1980s, this circuit can be found in commercial sound...
With the use of an additional diode and a resistor, the configuration of the figure can be...
This sound meter or sonometer was found in a Popular Electronics from the 80's. The circuit can be...