TOTAL = 850 rupees for this project , which is much much better than an arduino or a microprocessor operated electronic system
If more than 1 person enters when gate opened , gate only counts them as one person entered - To tackle this problem , we can attach a sanitiser dispenser to our photointerrupter box and make it compulsory to sanitise before entering , so that each person blocks the light in the photoelectronic circuit once and is counted . Another alternative I found to remove this problem is to think of a circuit which can detect whether a person is going in or out . This can probably be achieved by using 2 LDR light groups across the door and on the basis of which is triggered first and which later , it should respond accordingly (maybe this can be achieved by using 2 bistable multivibrators for each light , and then make a sequential circuit accordingly to do our work ).
If 16+people enter in a day and less than 16 leave , the substractor would have to get negative - This problem can be solved by using a comparator to find the bigger number , then activating 2 different substractors according to the comparator output , and then displaying the correct output , this model can also be used when there is another entry to the room , and there is a chance that more people left the room than entered .
If the environment is too bright , it may not be able to detect the interruption - To solve this problem , we can make sure that the photoelectronic part activates at a strong intensity of light and attach a strong light source to the box . Furthermore , shades can be developed over the cylindrical structure of box which can easily cover from sunlight / tubelight . And even this photoelectric mechanism can be replaced by infrared mechanism based on similar design .