This circuit is from the 1989 special edition of Radio Electronics Experimenter. The circuit was created with SMD components to be mounted on a keychain.
As part of a larger project, we found this modulation meter in the August 1994 Electronics Now...
The circuit shown in the figure is the version activated at the low level, of the previous circuit...
This is a high side smart current monitor circuit. The circuit is from a 2005 Linear Technology...