Automatic Lighting System using Arduino

The Automatic Lighting System using Arduino coordinates object detection and power switching to automate illumination based on occupancy. At the heart of the system is the Arduino Uno, which continuously monitors digital input signals from two FC-51 infrared (IR) sensor modules positioned at a doorway to detect entry and exit events. Each FC-51 module features an onboard IR transmitter and receiver; when a person passes, the reflected infrared beam changes the state of the sensor's digital output pin. By evaluating the sequence in which these two sensors are triggered, the microcontroller determines the direction of movement and tracks the current occupancy count inside the room. When the system registers that the room is occupied, the Arduino sends a control signal from a digital output pin to the base of a BC547 NPN transistor. Because the microcontroller's digital pins cannot supply enough direct current to drive an electromechanical relay coil, the transistor acts as a solid-state current amplifier. When biased into saturation by the microcontroller output, the BC547 allows sufficient current to flow from the 5V rail through the relay's electromagnetic coil, pulling the internal switch contacts closed. This action completes the circuit for the connected light bulb, turning the illumination on. Conversely, when the occupancy count drops to zero, the Arduino removes the base current from the BC547, de-energizing the relay coil and cutting power to the light bulb to conserve energy.