LDR Kit 1
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Description: Uses two transistors in a super-Darlington setup. By reading about all three Light/Dark Kits you will be able to decide which circuit is the best for your particular application. If your application is in very bright or very dark conditions then you can easily experiment with different resistor values to get better control over the switching range you need. There is nothing original in these circuits. We have taken them from published material (see end of this paper for References.) But we have redesigned them each onto similar PCB's to allow easy comparison. And in addition a light/dark option has been incorporated into each.
We say 'light/dark' because each circuit has a PCB mounted switch on-board. In one switch position a light-to-dark transition will activate the relay. In the other position a dark-to-light transition is required. So you can use the light falling on the detector to switch on a normally off circuit, or switch off a normally on circuit.