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The system will maintain control over the number of persons entering into a room. The main element in this circuit is a PIC 16F84A microcontroller. Light dependant resistor (LDR) is used as the detector. Laser beam is allowed to fall on the LDR in the normal condition. The LDR is connected to one of the inputs of a comparator. So in the absence of light the comparator output changes and which in turn gives interrupt to the microcontroller. Upon receiving this signal the micro controller takes calculations.
This LDR Laser arrangement can be placed in the entrance and exist. According to the signal, the controller triggers the counter circuit. i. e. if he signal comes from the entrance then the count increments by one and, if the controller gets interrupt from the exit ,the count decrements by one. Each time the magnetic lock is released for a short time for opening the door. Upon exceeding the limit, it will automatically seal the door and prevent further entry. Seven segment display and LED indicators are interfaced with the system for visualizing the status ever y time.
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