This circuit is from old documentation, using a component that cannot be found easily today. The indicator is a galvanometer, and the input voltage is in the order of 1 V.
This circuit was found in the March 1982 Radio Electronics magazine. The component is a special...
This 1969 Electronics World power supply has 5 V to power digital circuits and a 170 V output for...
Found in Radio Electronics from the 90s, this circuit uses a thermistor as a sensor that can have...