This circuit was found in a 73 amateur radio magazine from the 90s. An LED extends the scale from 0 to 5 V to 10 to 15 V in this bargraph circuit. Other zener values can be used.
We found this circuit in an old documentation from the 70s, but it can be assembled with modern...
Found in the January 1992 issue of Radio Electronics magazine, this circuit has its frequency...
This circuit was found in a NASA documentation from the 1980s. The components used are of the time...