This circuit with zener diodes was found in documentation from the 90s. The zener diodes determine the lighting point of the LEDs. The circuit is for 12 V automotive batteries.
This is another practical idea found in a 1997 documentation. This circuit allows a DJ to change the...
Found in a 90s Popular Electronics, this circuit can power a miniature railroad with voltages of 15...
Based on the frequency of the power grid, this circuit produces square signals for use in digital...