| 摘要 |
PURPOSE:To eliminate inconvenience of a DC impulse dial telephone set by adding a circuit outputting a signal equal to a pushbutton tone dial signal to the DC impulse dial telephone set and sending optionally a pushbutton tone dial signal after line connection. CONSTITUTION:An incoming bell ringing pulse signal is detected by a 16Hz pulse detection circuit 5 depending on the interrupting state of a hook switch 9, a detection signal is stored by a delay circuit 16 and a state holding circuit 17 and sent to a selection signal switching circuit 10. When a handset is hooked off, the hook switch is closed, the said telephone set and an opposite telephone set are connected via lines 8, 8' to attain required talking. The circuit 10 selects an output of a pushbutton dial signal generating circuit and when the handset is hooked off for the purpose of dialing, a sent signal by the pushbutton dial operation is a DC impulse. After the dialing, the selection signal switching circuit 10 selects the output of a pushbutton dial signal generating circuit by hooking off of the opposite telephone set.
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