Using components of the time, this 3 and half digit scale was found in an Electronics Now from the 90s. The circuit is powered by a 9 V battery.
This circuit, from a 1988 publication, consists of a timer that activates a relay at the end of a...
Found a documentation for PC from 1992, this circuit is indicated for the English power grid of...
This conventional window comparator configuration was found in an old documentation. It is valid...