Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relate~ to a deviee for connection
to a telephone li~e to render a ~elephone ~hereon incapable
of originating certain prohibited calls.
The obJect of the invention i9 to provide an improved
device, of this nature, which may be connected in parallel
across the ~wo wires of the telephone line, without xegard
to polarity~ and which terminates the telephone line only
for a short predete~mined period of time and only immediately
upon occurrence o~ a dialling pu]Lse, whereafter the telephone
line is again left unterminated~ whereby there is no
interference with company lines and apparatus.
Acoording to the present invention a telephone device
comprises:-
(i~ a computer including a memory and capable of beingprogrammed with one or more digits or sets of digi$s
which are intended to be prohibit0d, said computer
being adapted to compare the dialled pulses with
those of the prohibi~ed digit or digits, and to
originate an "allow~ function or a "prohibit" function
accordingly;
(ii) circuit terminating means, for connection across the
telephone line, connected to the computer and adapted,
upon receipt of said ~allow" function or said "prohibit"
function, to leave the line unterminated, or to
terminate the lin~, respectively~
In a preferred arrangement, the computer includes means
for conditioning the dialled pulses received ~rom the telephone
line, means ~or detecting the train of dialled pulses, means
for counting the dialled pulse train, and reject logic
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responsive to the counting means for producing an output
signal ~or controlling the circuit terminating means.
In order that the nature o~ the invention m~y be readily
ascertained7 an embo~iment o~ device in accordance therewith
is hereina~ter particularly described with rererence to the
figures o~ the accompanying drawings, wherein:
Fig.l is a block circuit diagram o~ the device;
Fig.2 is a circuit diagram of a power supply unit;
Fig.3 is n circuit diagram o~ a dial pulse conditioner;
Fig.4 is a circuit diagram of an "on~hook" detector;
Fig.5 is a circuit diagram o~ a coincidence gate;
Fig.6 is a circuit diagram of a memory latch assembly
and logic;
Fig.7 is a diagram of a terminating circuit.
Referring to Fig.l~ there is shown a block circuit
diagram of the telephone device intended ~or connecting across
the two wires of a telephone line. Terminals "T" ~or
connec~ion to the telephone line in either polarity, are
connected to the device through diodes "R". All units are
powered by a power supply A (fig.2) having connections ~Vcc
and -Vcc for a battery~ A gas protector llpn is connected
in parallel across the input. One Terminal "T" is
connected to the input of a dial pulse conditioner B~ the
output o~ which passes to a dial pulse counter F having
outputs connected to a coincidence gate J. Another output
of the dial pUlS& conditioner B passes to a dial pulse train
detector C, from ~hich an output is connected through a
dial pulse train counter G to other inputs of the coincidence
gate J.
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Outputs ~rom the dial pulse conditioner B and the dial
pulse train detector C also pass to an on~hoolc de~ec tor D
~rom which a first output passes to the dial pulse train
counter G for "0" re-set, and to a memory latches and logic
unit K for resetting.
A further connection is ma~e between the output of the
dial pulse train detector C and ~m end-of-train detector E~
and from there to an end~of~lool~ detector H ha~ing its output
connected to the dial pulse counter F for IIOtl xeset purposes.
Another connection is made between the output of the end-o~-
train detector E and the coincidence gate J,
The output of the dial pulse conditioner B is also taken
to the coincidence gate J and to the memory latches and
logic K.
Outputs from the coincidence gate J are taken to the
memory latches and logic K, and an output of the latter passes
to unit L which is an 88 millisecond one-shot re-triggerable
positive-edge trigger. Output from unit L passes to a
terminating circuit M~ and also to the input o~ the "on-hook"
detector D. The terminating circuit M has its inputs
connected respecti~ely to the $elephone wire terminals "T".
The dial pulse train detector C is a 20~ millisecond
one-shot re-~riggerable positive-edge trigger.
The end-of-train detector E is l-millisecond one-shot
re-triggerable positive-edge trigger.
The dial p~lse counter F~ and the dial pulse train counter
G are both counters of the kind known commercially under the
designation "4017".
The end-of-look detector H is a l-millisecond one-shot
re-triggerable negatiYe-edge trigger.
~he one-shot trigger units may be the kind known
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commercially under the designatio~ "4528 duals"~
The circuit terminating means are installed across the
telephone line such that termination o~ the line, resulting
from the dialling o~ a prohibited signal, makes the calling
o~ that prohibited num~er impossible.
The derice, when conne~ted across any telephone line,
renders all telephones on that line incapable of ~aking
prohibited callsJ e.g. long distance calls or information
calls. ~here there are a number of telephones OII a line
and it is desired to permit otherwise prohibited calls to
be made only from a certain selected telephone or telephone
there may be provided switching means located at each such
privileged telephoneg or otherwise convenienkly~ ~or
temporarîly disconnecting the device or rendering it non-
operative.
The device has only two terminals which can be connected
across the telephone li~e in either polarity and anywhere
along the telephone line, a~d the device per~orms its
~unctions without the need of external power other than a
small drain from the telephone line itsel~.
By way o~ stration of operation o~ the device, telephvne
dial pulses open the telephone line for 66 milliseconds for
each pulse, interspersed with terminat on of the line for
44 milliseconds between pulses. In the case of a "zeron
being dialled~ ~it being assumed that a zero at the com~encement
denotes a prohibitable call), the device of this învention
senses the tenth pulse starting~ and immediately terminates
the line ~or 88 milliseconds, thus eliminating the tsnth
pulse, and the prohibited nwmber "zero" as a ~irst digit.
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Any subsequent dlal pulses are likewise eliminated until
the unit senses an "on hook" condition (an open state lo~ger
than 88 milliseconds3, upon which the device re~sets its
memories.
In the case of the number ~41~1 (again assumed to denote
a prohibitable call) being dialled ~irs~, all subsequent
dialled pulses are ~horted out or eliminated until the
~on hook" condition ls sensed. This is correct in the
conte~t o~ there being no seven digit telephone numbers
commencing with "41~.
In the cass o~ direct-dial long distance numbers, e.g~
"1" followed by seven or ten digits, the second, third and
fourth digi~s are registered. If these digits are ~8"~
"O" and "O", (denoting certain long-distance call~ not
chargeable to $he caller) all eight or eleven digits are
allowed. If the second, third and fourth digits are not
"8n, "O" and "O", every dialled pulse a~ter the seventh
digit is elimina$ed or shorted out, until the "on hookl9
condition is sensed.
