| 摘要 |
PURPOSE:To discriminate the operating state of plural switches without increasing the modulation frequency and the number of transmitters by discriminating the switch state of each terminal device from a difference between a start bit pulse transmission time of a data collection center and a reception time of a response signal. CONSTITUTION:A control section CONT of the data collection center collects data and transmits a start bit pulse D0 to a transmitter Tx as transmission information at each prescribed period. The pulse D0 is modulated by the 1st modulation frequency f1 and the result is transmitted from an infrared ray emitting diode LED. Each terminal device (subscriber) is constituted as being incorporated with transceivers TR1-TRn and switches S1a-Snc in a terminal device. The signal from the terminal device is modulated by the frequency f2 in response to the state of the switches S1a-Snc and an infrared ray is transmitted as a response signal. The response signal is received by a receiver Rx of the center, the control section CONT discriminates simply the state of the switches S1a-Snc of each terminal device from the time difference between the transmission time of the pulse D0 and the response signal. |
