We have a project in which we have to count people entering in a room and automatically turn on the light when the first person enters the room and turn off the lights when the last person leaves i.e no one is there in the room anymore.

I was thinking of using 2 laser diodes and LDR to make a sensor and then monitor the order in which the sensor detects something for example if the 1st one detects an obstacle and than the 2nd it means someone has entered the room and vise versa.

Is there a budget (money or equipment)? 

12 minutes ago, AbdullahBaloch said:

We have a project in which we have to count people entering in a room and automatically turn on the light when the first person enters the room and turn off the lights when the last person leaves i.e no one is there in the room anymore.

I was thinking of using 2 laser diodes and LDR to make a sensor and then monitor the order in which the sensor detects something for example if the 1st one detects an obstacle and than the 2nd it means someone has entered the room and vise versa.

Do you mean two along a horizontal path? The time ordering tells you if they are entering or exiting?

Is the doorway big enough for two people at a time?

19 minutes ago, swansont said:

Is there a budget (money or equipment)? 

Do you mean two along a horizontal path? The time ordering tells you if they are entering or exiting?

Is the doorway big enough for two people at a time?

We have to create a model not an actual room. we have to use our own equipment but these parts don't cost much.

43 minutes ago, AbdullahBaloch said:

We have to create a model not an actual room. we have to use our own equipment but these parts don't cost much.

OK.

 

I think your dual-sensor system would work; it wouldn't be trivially fooled by a hand blocking one sensor since you would need two to trigger it, and the ordering tells you enter vs exit. If they were close enough then a simultaneous block confirms someone in the doorway.

(Still can be foiled by a burglar team with mirrors or flashlights, but that makes for fun cinema)