Smart Emergency Light

Now you need not fear dark nights when power breaks down. Here’s a white LEDbased emergency light that automatically turns on when mains power supply fails. The switching circuit is built around an NE555 timer (IC1), which is wired in monostable mode. When a low voltage is applied at trigger pin 2 of IC1, the timer activates and its output pin 3 goes high. It remains in that state until IC1 is triggered again at its pin 2. Light-dependant resistor LDR1 is connected between the positive supply of the battery and trigger pin 2 of IC1. Resistor R3 is connected between pin 2 of IC1 and ground. The resistance value of LDR1 remains high in dark (at night) and low in ambient light (in day time). This phenomenon is utilised to control the switching circuit. Working of the circuit is simple. In daytime, when ambient light falls on LDR1, its resistance decreases to make trigger pin 2 of IC1 high. As a result, output pin 3 goes low and the LEDs(LED1 through LED7) remain off. At night (in the dark), the resistance of LDR1 increases and a low voltage is applied to trigger pin 2 of IC1. This activates the monostable and its output goes high to make all the LEDs glow. Learning: Application of NE555 inastable mode. Application of LDR in light and dark. Application of bridge rectifier. Brand: Kits'n'spares, Marketed by: Kits'n'spares