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.
This circuit was found in a former Popular Electronics. The timing is set on the potentiometer and the...
This circuit transmits signals to an FM receiver at a distance of up to a few tens of meters. The...
This circuit was found in a 1969 US documentation. It provides a signal that can be externally...