Automatic Evening Light With Cut-Off Timer

The Automatic Evening Light With Cut-Off Timer operates through an integrated chain of analog signal conditioning, switching, and timing stages powered by a 12V battery or adaptor. At the input stage, an LDR1 (Light Dependent Resistor) combined with resistors forms a light-sensing voltage divider that monitors ambient light levels. When evening arrives and ambient light drops, the resistance of LDR1 changes, altering the voltage input to the LM358 dual op-amp (IC1). Configured as a comparator, the LM358 detects this voltage threshold shift and drives its output high as dusk falls. This output controls a 2N3904 NPN transistor (T1), which acts as a solid-state switch to energize the 12V SPST relay (RL1). Once triggered, the relay closes its contacts to switch on the 60-watt mains-powered bulb. Simultaneously, the circuit incorporates a timing mechanism utilizing a large 1F 2.7V supercapacitor and a 220µF 25V electrolytic capacitor alongside 1N4007 rectifier diodes (D1-D5). As the circuit operates, the capacitor network charges and slowly discharges over a preset duration. Once the stored energy depletes below the necessary reference threshold, the op-amp state reverts, turning off transistor T1 and de-energizing relay RL1 to automatically cut off the lamp after a few hours. Two 5mm LEDs (LED1 and LED2) provide visual status indication for power and operational states, while standard resistors (10kΩ, 4.7kΩ, 1kΩ, and 560Ω) handle current-limiting and biasing across the entire discrete analog layout.