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.
The circuit shown in the figure below is from the 1993 Linear Technology Applications. The...
In the figure we have the way to implement the E (AND) function with two inputs, in the case of...
This circuit can be used both as a power source and as a battery charger. The resistor R1 serves as...