Light Detector

This circuit provides a com- puter with information about the presence of daylight. Poss- ible applications include auto- matically measuring the dur- ation of the daylight period in an autonomous weather station, or in control systems for outside lighting around the home. The computer can be programmed to monitor the output of the light detector, and automatically arranges for the relevant lights to come when it gets dark. The circuit is simple enough to enable ready construction on a piece of veroboard. Its output is TTL compatible, and logic low when the phototransistor de- tects light. The sensitivity can be made adjustable for par- ticular requirements by replac- ing R, with a series connected 10 K4 preset and a 270 Q sistor. St 5V L -40 IC 2 0 • ®5V 5mA 8 SUPPLEMENT LIGHT DETECTOR re- N1 = 1/2 IC2 = 74LS13; 74HCT13 5mA 87409