PB SIGNAL AUTOMATIC CHANGEOVER TELEPHONE SET

PURPOSE:To improve the operability according to automation by switching the mode to the pushbutton signal sending position automatically in a timing from the end of dial pulse signal transmission so as to attain the service of a PB signal during the talking without manual operation. CONSTITUTION:A key pad circuit 9 is connected to a dial pulse DP signal transmission circuit 7 or a pushbutton PB signal transmission circuit 8 via a switch 10A. When a handset is hooked off, a hook switch 4 is closed to form a channel via a relay circuit 2. When a voltage is received from the exchange side, a timer start circuit 5 is started to set a timer 5a. In this case, a selection circuit 10 is started to change over the position to the DP signal sending position forcibly. When the timer start circuit 5 detects the interruptnig of a channel, the timer 5a is reset again. A register signal is on the position of the DP signal sending during the timer start. When several seconds (4-6sec) elapse when no interruption of the channel is detected, the timer goes to timeout, the selection circuit 10 is started and the position is switched to the PB signal sending side. The succeeding register signal is sent in a form of the PB signal.