This circuit is for 12 V batteries but can be used with batteries of other voltages by changing the zener diode. The trigger point is adjusted by R1. The operating system accepts equivalents.
In the figure we have a simple logic level indicator for TTL circuits or powered by 5 V....
This circuit was obtained from the December 1990 issue of Radio Electronics magazine. The circuit...
This power supply for gas laser (HeNe) was found in a 90’s Popular Electronics. It generates from 1300...