| 摘要 |
PURPOSE:To discriminate an incoming sound from the other ones by using a buzzer with the peak of resonant sensitivity in two frequency positions as the sounding body of a mobile radio telephony equipment and generating more than two different frequency incoming sounds with the peak of sensitivity by the buzzer when doorphone incoming call is received. CONSTITUTION:When receiving the doorphone incoming call, signals with frequency f1 and f2 are alternately supplied to the base of a transistor 43 with duration T1 and T2 respectively from a terminal FQ of a control circuit 46. On the other hand, a terminal ENV of the control circuit 46 is in the state of 'low bell' during the ringing period of each duration of T1 and the first half of T2, and 'high-impedence' during the last half of envelope. In this way, the envelope whose frequency f1 and f2 becomes gradually getting smaller, is added in the envelope period, and the doorphone incoming sound, similar to a chaim sound as the intercom sound by the two sounds of frequency f1 and f2, is obtained. Thus, the doorphone incoming sound can be easily discriminated from the other incoming sound such as inner line incoming sound even when it is the buzzer.
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