Description: We provide 3 complete and separate Light/Dark LDR circuits each with a relay on-board all in the one kit. Each is a simple well tried circuit: one uses two transistors in a super-darlington setup, the second uses a LM741 op-amp while the third uses a Schmidt Trigger. Each board has a PCB-mounted switch to convert the circuit from light to dark switching and vice versa. There is nothing original in these circuits - they have been around for years. What we have done is bring three good timer circuits together all in the one Kit for you to build & experiment with. Uses a LM741 op-amp. PCB dimensions 2.4" x 1.5"