light-sensitive switch

by H Huynen light-sensitive switch A = on B = auto C = oft R1 R2 R6 T1 U C4 DI TIL81 BP103 1N4148 O 4704 e 25V B80C1500 T3 oA B C EZE T2 BC547B Cll 1y 16V 15V R4 R5 BC547B R7 P2 500k U 3 CalI 1p 116V 78L12A 86500 This switch is energized by light and can, therefore, be used, for instance, to switch on the aquarium lighting in the morning. Both the sensitivity and the hysteresis of the circuit can be preset; Re is energized in the pres- ence of sufficient light. The sensor is an n-p-n phototransistor Type TIL8I or BP103, which conducts 1:1 EE July/August 1986 When the current in T1 is large The sensor may also be a photodiode enough, some will flow through R4 or light-dependent resistor (LDR), but when light falls upon it. The conse- quent current is divided between T2 slightly, the circuit will not revert to and R4-C1. Since T2is connected as a current source, no current will, how- ever, flow through R4-C1 as long as the current in Ti is smaller than that through T2as determined...