i saw a project, MICROCONTROLLER BASED PARKING WITH SECURITY SYSTEM using 89C51,in that they have used an Entry Sensor Ckt and an Exit Sensor Ckt and their outputs are given to a Signal Conditioning Ckt before applying it to microcontroller ,can anyone tell me which ckt would be used as entry sensor and exit sensor and why signal conditioning ckts are used before uc.
(i'm a newbie to microcontroller)

 

You use two light beams. The order in which they are broken indicates coming in or going out.

Interfacing the world to a microprocessor is a somewhat lengthy subject. You can look here - http://www.upscale.utoronto.ca/GeneralInterest/MicroP.html - or else pursue some books on the subject.

This sounds like a good starter project for getting into microprocessors. You will probably be more successful if you take the time to learn more about how they function, and enough electronics to understand the external circuits.