This circuit emits a warning sound when night falls. The circuit is from a Hands On Electronics from the 90s. The Sensor is a common LDR and R6 adjusts the trigger point.
This is one of many timer settings with the 555 found on this site. This is the traditional...
This circuit is from the American magazine that no longer exists Science & Electronics,...
This is the basic configuration of many LM339 manuals, as a comparator with hysteresis. The font...