Hi ,
Let me explain more in details, the idea is use on Home Automation, to switch on light or air-cond or anything.
If design use normal simple side beam sensor, or PIR sensor, the system can detect someone is enter, hence turn on lighting. But, when to turn it off? the system must detect the person is leaving . For example , If two person is enter living room, after a while, one is going out, the other one is still stay inside, the system won;t know there is still people inside, so by counting how many is in, how many is out, will be better solution.
May be someone will suggest putting PIR sensor at the living room to detect present of human, but PIR will not work if the humun is not moving. By other sensor like radar and etc, may not practical to install and cover whole living room.
So I come out idea on counting number of person in and out for the control, it just an idea only.
So, It shall use indoors, can be any size , depend on number of sensors. The environment can be light or dark, IR proximity shall be the cheapest solution as I think. (not consider camera)
Thank you,
Victor