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.
Books and e-Books by Institute NCB 100 CIRCUITS - SHIELDS FOR ARDUINO FUN PROJECTS FOR THE...
The LM109 was manufactured by many semiconductor companies that presented different configurations in their...
This shield was found in an American documentation from the 70s. The operational amplifier is from...