Flood alarm (CB7994E)

This circuit is from a 90s Popular Electronics. The transistors are of general use and the buzzer is a Sonalert type.

Low distortion oscillator (CB9200E)
This Wien bridge oscillator was found in a 90's EDN. The components are from that time and the...
Liquid Level Control (CB5311E)
The purpose of this circuit is to maintain the liquid level of a reservoir between two values...
Comparator with different voltages (CB5976E)
In the figure we have the way to use a voltage comparator powered by a voltage to control a...