The description of the project as follows:
I want to count the number of people in a building as well as in every room.
Let's assume that the building is empty at the beginning, and the building has 4 entrances, and 50 rooms, each room has 1 door.
My idea is to design a unit that consist of arduino board, ultrasonic sensor and wireless module. and put this unit on each door so it will count locally whoever enters or exits the building and the rooms. and then send this information to the master. On master software will process all information and display the results.
What is the best way to achieve this ? what are the suggested boards, sensor and wireless module and its communication protocol ?