| 摘要 |
In the combination of a call unit (20) for an emergency call system with a remote trigger device (54), the call unit incorporates means for transmitting and receiving speech and/or data via the public switched telephone network (PSTN) in a hands-free mode. The remote trigger device (54), which may be a pendant (54) includes a keyboard (56) connected to a signal transmitter for remote operation of the transmitting and receiving means. The call unit includes a telephone line seizing system which comprises an actuating circuit and a seizing circuit. The actuating circuit comprises a resistor (82) for limiting current drawn from the PSTN, a switch (86) to make and break the actuating circuit and a darlington transistor (90) actuated by the actuating circuit to complete the seizing circuit and thereby seize the telephone line. The system will work to allow outgoing calls even if there is a mains electricity power cut. |
