Keypad caller for a telephone set

Details Keypad caller for a telephone set Keypad caller for a telephone set

1980-11-18

1982-04-27

Brigance, Gerald L.

Communications: electrical

Land vehicle alarms or indicators

Internal alarm or indicator responsive to a condition of the...

340365E, H04M 150

Patent

active

043272550

ABSTRACT:
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.sup.+,V.sup.-) voltage supply to the oscillator 50 as well as switching a double switch (Q10, Q11) which switches the speech current.
Applications: telephone telecommunications.

REFERENCES:
patent: 3648202 (1972-03-01), Schazkwisk
patent: 3971896 (1976-07-01), Sekiguchi
patent: 3978474 (1976-08-01), Engstrom
patent: 4007459 (1977-02-01), Hazelbarger
patent: 4086588 (1978-04-01), Kawanabe et al.
patent: 4196318 (1980-04-01), Nelson

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