This circuit is from an 80's Electronic Engineering. The base is a common operating and 4 single integrated voltage comparators. The circuit directly drives 4 indicator LEDs.
This traditional configuration that any Series 139 comparator can use is found in the 1990...
The circuit shown in the figure can be used to detect vibrations or to provide amplified acoustic...
This toy organ was found in Popular Electronics from January 1967. It can be constructed from...