| 摘要 |
PURPOSE:To miniaturize the whole of a circuit and improve reliability by reducing the number of parts. CONSTITUTION:A plurality of indoor control units 12, 12... are connected through a transmission line 2b composed of a positive side signal line 21 and a negative side signal line 22. A DC super position circuit 60 is provided between both signal lines 21, 22, which includes a DC power supply 63 for applying predetermined DC voltage. There are further provided in each indoor control unit 12, 12... a transmission circuit 30 and a reception circuit 40 both for an information signal, and a polarity judgement circuit 50 for judging the polarity of each signal line 21, 22. Accordingly, two discharge resistors 6a, 6b are provided between the DC power supply 63 and each signal line 21, 22 for discharging residual electric charges, and a capacitor 6c is connected in parallel with the DC power supply 63 for reducing impedance of the transmission line 2b to a predetermined value. |
