| 摘要 |
PURPOSE:To reduce the sound volume of a click sound at a receiver during the transmission of a dial pulse by making the mute terminal of a dial IC into 'H', making the transistor (TR) of a muting circuit come to ON, and grounding both the ends of a telephone set through a resistor. CONSTITUTION:In response to a key input from a key board, the dial pulse output terminal DP of the dial IC repeats a high level 'H' and a low level 'L', and the TR Q1 comes to ON and OFF. When the TR Q1 comes to ON and OFF, the TR Q2 and TR Q2 come to OFF and ON, and the dial pulse is transmitted to a trunk line through a rectifying device 20. Then, while the dial pulse is being transmitted, the mute terminal MUTE of the dial IC comes to the high level 'H and the TRs Q3 and Q4 come to ON. Thus, because both the ends of the receiver are grounded through the resistors R7 and R10, the sound volume of the click sound heard from the receiver is reduced.
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