This Schmitt optical trigger with LDR was found in old documentation. The relay must be sensitive, or an additional step must be used to trigger it.
Disabling this circuit from a 2002 documentation can only be done by pressing 4 keys in a correct...
This circuit was obtained from a manual of the integrated circuit itself, but can be applied to...
This simple 2004 circuit uses a common sensor used in television and other equipment. It checks...