The following brief explanation was provided by Miss Surya for getting a better view of the proposed circuit design of an automobile automatic dimmer cum dipper head light switch circuit with an optional cell phone charger circuit for facilitating the charging of a cell phone also on board.
Here the IC 555 has been used not as a charging indicator rather as a comparator for controlling the dipping action of the head lamps.
The use if IC 555 as a charging indicator would have made the circuit unnecessarily complicated, therefore a novel and simpler way is selected for the charging ON indication.
The LED connected across the 5 Ohm watt current limiting resistor effectively indicates the charging status of the cell phone and switches OFF the moment the charging process stops.
The IC 555 works like a comprartor here, when light falls on the LDR, voltage at PIN#2 rises above the set internal threshold which prompts the IC to change its output PIN#3 voltage from 0 to 12, triggering the connected relay.
The relay contacts immediately transfer the positive supply from the "high" filament to the "low" filament of the head lamps, resulting in an instant dipping of the lamp intensity.
The LDR must be positioned in such a way that it only receives light rays coming from front of the vehicle, which will be mostly the lights from another vehicle's head lamps.