IR object counter help. Urgent! :O

[will.joyc]

Hello all
For uni i'm doing a circuit design project and my design is for an Infrared Object counter alarm system. Basically I want a system with two IR sensors, one for incrementing the count, and the other for decrementing. The count will be displayed on a seven segment display, which when a certain value is hit, an alarm will sound. Essentially my system will be implemented to a room, on the entrance and the exit. When say, 10 people have entered the room, I want the alarm to sound, and the Entry IR sensor to deactivate, only allowing people to leave. Once the value displayed is less than 10, the entry IR sensor will turn on again.

I want to use RE200B IR sensors, LM741 IC's (As comparators) 4510 BCD up/down counter, 4511 seven seg driver, and a piezo alarm. Im not sure if my design is possible, was wondering if anyone could give me a hand in designing such a system. Any help would be much appreciated
Will