PIR based smart lighting system

This circuit will turn on a device preferably a light bulb for a fixed duration of time when it detects movements. this circuit is connected in parallel with a pre-existing switch for the device.Taking example for a light bulb, when a person walks into a room, the device turns ON for a fixed duration of time. If the person wishes to stay in the room for a longer duration, he can turn on the switch manually, since it is a parallel wiring.

This circuit can be used in various applications like staircase lighting or for a room. when someone passes the light turns ON and automatically turns OFF, there by saving a lot of energy.
The heart of the circuit is the PIR module, which sends out a +ve pulse when it detects a movement. PIR stands for Passive Infrared Receiver, implies it does not have a source of IR radiation. some modules have an option for both +ve or a -ve pulse when the motion is detected. the module I secured had the option only for a positive pulse.
The second part of the circuit is the timer. I have used the famous IC555 in the monostable mode to generate the time delay.Refer the IC555 datasheet for the formulae to calculate the resistor and capacitor value for the desired delay. the trigger for IC555 should be a negative pulse, since my module provided only a positive pulse, I used and NPN BC547 transistor as NOT gate to invert the logic. I connected the output of the IC555 to a 5V relay to drive the mains operated devices such as LED or CFL or fluorescent tubes.

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