System making it possible to control periodically the presence or absence of people in one or more locations determines

摘要

The attendance monitoring system has a terminal (1) in each room to allow entry of attendance information. This is connected to the AC mains which act as a carrier to send the information to a central computer (3) which collates, records and displays the attendance information. The terminals are hand-held devices built round a microcontroller. The terminals have a keyboard and a display. A connector (10) on the terminal allows it to be linked (11) by cable to the modulator-demodulator unit (2) which plugs into an AC mains wall socket. The information from the terminal is used to modulate the carrier from the modulator unit. A similar unit (19) connects to the main computer.