| 摘要 |
A keypad caller which can be fitted into a conventional telephone set, includes a two-frequency oscillator (50) which emits two sinusoidal frequencies chosen from eight when a key (1, . . . 0) is depressed thereby selecting the frequency-determining resistors of the oscillator (50) and switching the (V+,V-) voltage supply to the oscillator 50 as well as switching a double switch (Q10, Q11) which switches the speech current. Applications: telephone telecommunications.
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