Hi.....I wish to do a small project as follows:
When a person enters a room the lights must switch ON automatically,when everyone has gone out the lights must switch OFF.How to achieve this?...........Thanks for everyone replying for this....

 

Hi.....I wish to do a small project as follows:
When a person enters a room the lights must switch ON automatically,when everyone has gone out the lights must switch OFF.How to achieve this?...........Thanks for everyone replying for this....

You can put a sensor on the room's door to count the people going in and out of the room. If the difference of the people going in to the people going out is zero then the lights will turn off otherwise they will turn on. Another option is to use infrared sensors on the walls insight the room to detect the presense of people. There are ready infrared sensors in the market which are used for this purpose (detect thinks and persons to turn on lights or whatever).