Device for blocking toll calls from subscriber telephones
阅读：772发布：2021-03-24
专利汇可以提供Device for blocking toll calls from subscriber telephones专利检索，专利查询，专利分析的服务。并且To prevent the unauthorized initiation of toll calls from a subscriber station of a telephone system, the telephone set is equipped with monitoring circuitry working into a binary/decimal counter which is activated during the dialing of the first (or some other specified) digit and, in response to one or more predetermined values of that digit, trips a flip-flop to place a shunt across the line loop with concurrent generation of a busy signal. The flip-flop is also tripped if dialing is commenced before reception of a dial tone from the central office. To prevent the generation of a spurious dial tone by voice frequencies, the microphone of the telephone receiver is shortcircuited during dialing. The monitoring device, which can be manually switched off by an authorized operator, is continuously energized by the voltage drop developed across a shunt network in a quiescent state and across a series network in an active state.，下面是Device for blocking toll calls from subscriber telephones专利的具体信息内容。
1. A device for blocking the initiation of certain outgoing calls, characterized by a predetermined value of a specified call-number digit, from a subscriber station of a telecommunication system connected via an outgoing line to a central office, comprising: monitoring circuitry at said station connected across said line for detecting dial pulses generated at said station by a call selector periodically opening and closing a line loop; pulse-shaping means in said circuitry for generating trains of stepping pulses in the rhythm of said dial pulses and for deriving an individual digital pulse from any such train; an electronic pulse counter connected to said circuitry for receiving said stepping pulses therefrom, said counter having at least one output lead electrically marked in response to a predetermined number of consecutive stepping pulses; control means connected to said pulse-shaping means for enabling said counter only in the presence of a predetermined digital pulse in a sequence of such digital pulses; and electronic switch means connected to said output lead for shunting said call selector, thereby preventing effective opencircuiting of said line loop and attenuating the dial pulses transmitted to said central office; said circuitry further including a detector for alternatingcurrent signals from said central office and discriminating means connected to said detector and pulse-shaping means for determining the presence of a dial tone from the central office prior to generation of the first stepping pulse and, upon the occurrence of a stepping pulse in the absence of such dial tone, for operating said switch means independently of said counter.
2. A device as defined in claim 1 wherein said station is equipped with an electro-accoustic transducer for transmitting voice signals over said line, further comprising disabling means for said transducer connected to said pulse-shaping means for preventing the transmission of such voice signals during dialing, said disabling means being controlled by said detector for reactivating said transducer in response to central-office signals.
3. A device as defined in claim 1, further comprising a protective circuit ahead of said detector for suppressing transients in the input thereof.
4. A device as defined in claim 1 wherein said circuitry further includes differentiation means responsive to the first digital pulse after initial closure of the line loop for generating a reading pulse at the end of said predetermined digital pulse, the connection between said output lead and said switch means including normally blocked gate means controlled by said differentiation means for unblocking by said reading pulse.
5. A device as defined in claim 4, further comprising blocking means for said counter connected to said differentiation means for actuation by said reading pulse and to said discriminating means for deactivation in the presence of a dial tone.
6. A device as defined in claim 4, further comprising delay means connected to said differentiation means and said counter for resetting the latter a predetermined period after the occurrence of said reading pulse.
7. A device as defined in claim 1, further comprising a continuously operative power supply for said circuitry, said power supply including a first network bridging said line for developing a voltage drop in the open-loop condition and a second network in series with the line for developing a voltage drop in the closed-loop condition.
8. A device as defined in claim 10 wherein said first network is provided with a d-c output terminal energizing said circuitry, said power supply further comprising a d-c/d-c converter connecting said second network to said terminal.
9. A device as defined in claim 1, further comprising a tone generAtor controlled by said switch means for placing a busy signal on said line concurrently with the shunting of said call selector.
10. A device for blocking the initiation of certain outgoing calls, characterized by a predetermined numerical value of a specified call-number digit, from a subscriber station of a telecommunication system connected via an outgoing line to a central office, comprising: monitoring circuitry at said station connected across said line for detecting dial pulses generated at said station by a call selector periodically opening and closing a line loop; pulse-shaping means in said circuitry for generating trains of stepping pulses in the rhythem of said dial pulses and for deriving an individual digital pulse from any such train; an electronic pulse counter connected to said circuitry for receiving said stepping pulses therefrom, said counter having at least one output lead electrically marked in response to a predetermined number of consecutive stepping pulses; control means connected to said pulse-shaping means for enabling said counter only in the presence of a predetermined digital pulse in a sequence of such digital pulses; and electronic switch means connected to said output lead for shunting said call selector, thereby preventing effective open-circuiting of said line loop and attenuating the dial pulses transmitted to said central office; and a continuously operative power supply for said circuitry, said power supply including a first network bridging said line for developing a voltage drop in the open-loop condition and a second network in series with the line for developing a voltage drop in the closed-loop condition.
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