This circuit detects when there was a power cut, triggering the indicator circuit around it. The circuit is powered by the voltage of a source connected to the grid.
In fact, we can say that this circuit found in documentation from the 90s, consists of an intercom...
The basic integrated circuits of this 1988 multimeter are no longer very common today, but if...
This circuit is from an old publication of the 70's. It can be implemented with modern transistors like the...