This simple three-LED sensor uses an NTC at the input. The circuit is based on an uncommon integrated component today. We found it in documentation from the 80s.
This proximity (capacitive) alarm triggers a relay that, in turn, triggers an audible warning...
This sensitive circuit was found in old documentation. The SCR can be any of the 106 series and...
This traditional multivibrator configuration uses an LDR as a sensor. The circuit emits sound when...