DESIGN AND CONSTRUCTION OF A FENCE LIGHT CONTROLLER

ABSTRACT This project work is titled automatic fence light controller. The project, construction of automatic fence light controller was designed to trigger a relay to operate an AC lamp at Sunset. The lamp remains on till morning and then turns off. This eliminates the need of switching the fence lamp daily and also helps to light the premises of the house when the occupants are out of station. The system makes use of light sensor to operate. The light sensor used is the ORP12 photocell. In bright light the resistance of the ORP12 can be as low as 80 ohm and at 50lux (darkness) the resistance increases to over 1M ohm. The 1M control should provide a wide range for light intensities, if not its value may be increased. The op-amp senses the voltage difference between pins 2 and 3. The control VR1 is adjusted so that the relay is off, the output of the op-amp will be around 2 Volts. When light falls, the resistance of the photocell increases and the difference in input voltage is amplified by the op-amp, the output will swing towards full supply and drive the transistor and relay. The 270k resistor provides a small amount of hysteresis, so that the circuit switches on and off with slightly different light levels. This eliminates relay chatter. Take great care if you decide to wire the relay to activate a mains lamp. Make sure the relay contacts provide adequate isolation and have ample rating for the load. The very fundamental reasons behind this project assignment is to expose student to the very important aspect of private and independent research work not only theories but also subsequent translation of the theoretical research work into a particular function system.