This circuit is from a Radio Electronics from December 1964. The components are from the time and modern equivalents for transistors and diodes can be used.
The frequency of this circuit depends on C1 and, for the indicated values, it is 1 kHz. Equivalent...
Taking advantage of the comparator setting, we can use the Norton amplifier as an over temperature...
This old indicator circuit indicates only when the fuel reaches the sensor level. The integrated circuit...