This circuit was found in the March 1984 issue of Radio Electronics magazine. The sensor is a transistor. The module is a common type at the time.
In relation to the previous circuit (CB18493E) this spy has an extra transistor, which can be a...
We found this sophisticated meter circuit in an article in Radio Electronics magazine from June...
The circuit used is the 4093 configured as an inverter in this application from Radio Electronics from...