JPH0375660U - - Google Patents

Description

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the automatic switching device for public telephone lines according to the present invention, Fig. 2 is a waveform diagram of the starting voltage applied to the public telephone, and Fig. 3 is a diagram of a conventional switching device. A circuit diagram showing the configuration, and FIG. 4 is a waveform diagram of billing pulses. L1, L2...Public telephone line, 1...General telephone, 2...Hook state detection circuit, 3...Polarity reversal detection circuit, 4...Threshold circuit, 5...Public telephone, 6...Charging pulse removal circuit, 7, 9 …flipflop,
RY-1, RY-2...Relay.

Claims (1)

[Scope of utility model registration claim] Interposed between the first terminal and the public telephone line,
a hook state detection means for detecting on-hook and off-hook of the first terminal; and a public telephone that is a second terminal is normally connected to the public telephone line, and when switching is activated, the second terminal is connected to the public telephone line. switching means for disconnecting; means for prohibiting a call by the first terminal based on a drop in line voltage due to use of the second terminal; a switch control means that switches and operates the switch means until the on-hook is detected; a first timer that measures a first preset time after the hook state detection means detects the on-hook; and the first timer a second timer that measures a second preset time from the time when the second timer finishes timing, and while the second timer is measuring,
and means for applying a predetermined negative voltage to the second terminal.