counter circuit

[lepton]

I want to make a project in which I have to use an electronic circuit which will count the no of people passing at a particular entrance in a given time interval and this number or equivalent signal (propotional voltage) can be used as a input for subsequent part of my project circuit.Suggest any possible circuit.

 

[Russlk]

Light source, detector, counter IC. what do you plan to do with the number when you get it? You have to give more info if you want useful feedback.