GB2243050A

GB2243050A - "Telephone call control device"

Info

Publication number: GB2243050A
Application number: GB9008465A
Authority: GB
Inventors: Brian Maclean Leroy Marten
Original assignee: PULLWAY Ltd
Current assignee: PULLWAY Ltd
Priority date: 1990-04-12
Filing date: 1990-04-12
Publication date: 1991-10-16
Anticipated expiration: 2010-04-12
Also published as: EP0545937A1; GB2243050B; GB9008465D0; WO1993000762A1

Abstract

A telephone call control device comprises a casing (1) for attachment to the housing of a freely accessible telephone socket, a control plug (15) carried by the casing for engaging in the telephone socket when the casing is attached, a control socket (21) carried by the casing for receiving the plug of a communications apparatus to be connected to the telephone socket, and control circuit means in the casing for electrically connecting the control socket and the control plug. The control circuit has a call-restricting operating condition in which, following dialling from an apparatus connected to the control socket, the control circuit monitors the transmission on the line and, in the absence of a predetermined carrier signal, disconnects the line. <IMAGE>

Description

"Telephone call control device" THIS INVENTION relates to a device for controlling the use of a telephone socket, particularly a telephone socket intended for dedicated use by communications apparatus, such as a facsimile machine, which delivers a continuous carrier signal to the telephone line during operation.

Modern telephone handsets and other communications apparatus, including facsimile machines, for connection to the telephone system are commonly provided with a plug which is adapted to plug into a freely accessible telephone socket. Such sockets are open to abuse by parties other than the subscriber making unauthorised outgoing calls via the socket.

In many offices, personnel are deterred from making personal telephone calls using the lines dedicated to voice telephone calls because any resulting telephone call will be logged through the switchboard.

There is, however, in most offices one telephone line, namely the line dedicated to Pacsimile transmissions, which is oDen 24 hours a day and by-passes the switchboard, thereby enabling unauthorised telephone use.

The present invention aims to provide a call control device for a telephone socket intended for use with a facsimile machine or like communications apparatus in order to enable the subscriber to limit the use of that socket exclusively to transmissions from the apparatus.

Accordingly, the present invention provides a telephone call control device comprising a casing for attachment to or adjacent to the housing of a freely accessible telephone socket, a control plug carried by the casing for engaging in the telephone socket when the casing is attached, a control socket carried by the casing for receiving the plug of a communications apparatus to be connected to the telephone socket, and control circuit means in the casing for electrically connecting the control socket and the control plug, the control circuit having a call-restricting operating condition in which, following dialling from an apparatus connected to the control socket, the control circuit monitors the transmission on the line and, in the absence of a predetermined carrier signal, disconnects the line.

In order that the invention may be more readily understood, an embodiment thereof will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a front view of a telephone call control device embodying the present invention; Figure 2 is a side elevational view of the call control device; Figure 3 is a rear elevational view of the device; Figure 4 is a front view of the call control device with a detachable middle part of the casing front wall removed and showing hidden detail; Figure 5 is a front view of a control cam operated by a lock of the call control device; Figure 6 is a side view of the control cam as seen in the direction of arrow X in Figure 4; Figure 7 is a side view of the control cam as seen in the direction of arrow Y in Figure 4; and Figure 8 is a circuit diagram of an electrical control circuit of the call control device.

Referring firstly to Figures 1 to 3, a telephone call control device embodying the present invention comprises a casing 1 which is moulded from suitable plastics material and is intended for attachment to the housing of a freely accessible standard telephone socket intended for the dedicated use of a facsimile machine.

The casing 1 has a front wall comprising of fixed upper portion 2, a fixed lower portion 3 and a detachable middle portion 4.

The upper fixed front wall portion 2 is provided with a control socket aperture 5 and a projecting lock housing 6 accommodating a cylinder lock 7 operable by a key 8 (Figure 2). An indicator window 9 is formed in the front wall portion 2 above the lock housing 6 and an indicating portion of a control cam 10 rotatable with the lock 6 behind the casing front wall is visible through the window 9. An area 11 of the fixed wall portion 2 is upwardly and rearwardly inclined and recessed to receive adhesive labelling carrying operating instructions.

Figure 2 shows that a control plug 15 is supported by the casing 1 so as to project from a rear wall 16 of the casing. This plug 15 has the configuration of a standard telephone plug and is adapted to be received in the standard telephone socket to be controlled by the control device. The plug 15 engages in and makes electrical contact with the standard telephone socket when the casing of the device is attached to the housing of the telephone socket using the existing fixing screws for the front plate of the socket as hereinafter described.

A printed circuit board 20 is mounted on a detachable upper portion 17 of the rear wall 16 of the casing 1 so that the circuit board is positioned in the upper part of the casing 1 behind the fixed upper part 2 of the front wall of the casing. The circuit board 20 carries on its front face a control socket 21 which has the configuration of the standard telephone socket and is positioned on the printed circuit board so as to register with the socket aperture 5 in the casing front wall. A microswitch 23 is also mounted on the front face of the circuit board and has a switch operating arm arranged for actuation by the control cam 10 upon operation of the lock 6. In the illustrated position of the lock 6 and control cam 10 the switch 23 is closed.The circuit board is also provided with printed conductors connecting the electrical terminals of the control socket 21 to the corresponding terminals of the control plug 15 via control circuit illustrated schematically at 25 in Figure 3.

A lower portion of the casing defines behind the fixed lower part 3 of the front wall a battery compartment 26 for receiving and retaining a 9 volt battery 27 which powers the control circuit 25 and is connected to power input terminals of the printed circuit board 20 by a suitable connector arrangement 28. The battery compartment 26 has a removable cover 29 (Figure 3) which is simply clipped to the back of the casing 1.

The detachable middle part 4 of the front wall of the casing 1 constitutes a security cover removable from the casing to provide access to mounting holes 33 formed in a fixed rear wall portion 34 of the back wall 16 of the casing. Several pairs of mounting holes 33 are provided to enable the control device to be attached to telephone sockets using screws engaging in existing threaded bores provided in the housing of the telephone socket for front plate fastening screws of the socket, which screws may have any one of several different spacings. After attachment of the device to a telephone socket, the security cover 4 is replaced so that it covers the screws attaching the device to the telephone socket.

The construction of the control cam 10 is shown in Figures 5, 6 and 7. The cam 10 comprises a hub 40 adapted to be mounted on the barrel of the lock 7 for rotation therewith. Attached to the hub 40 is an arcuate cam dise 41 having a security cover locking segment 42 and a switch operating segment 43 of smaller diameter than the locking segment 42. A portion of the operating segment 43 is displaced rearwardly to constitute a switch actuating arm 44 and is arranged to hold the switch 23 closed when the cam is in the angular position shown in the drawings. The segment 43 of the cam disc is formed with a peripheral flange 46 and two regions of the surface of the segment 43 and its flange are provided with coloured indicator elements 47 and 48, the first of which is red and the second of which is green. In a first call-restricting position of the control cam 10 shown in the drawings, the red indicator element 47 is displayed in the indicator window 9 and indicates that the actuating arm 44 is positioned to close the microswitch 23 and thereby energise the control circuit to monitor outgoing calls made via the socket to which the device is attached. At the same time, the locking segment 42 of the cam is located between the front wall and the locking tab 34 of the security cover 4, thereby preventing removal of the security cover and thus access to the screws attaching the device to the telephone socket.

Rotation of the control cam 10 anti-clockwise 0 through 90 from the illustrated position into a second position by operation of the lock 6 brings the green indicator element 48 into the indicator window 9 and rotates the actuating arm 44 of the cam 10 out of engagement with the microswitch 23, thereby opening the microswitch, deenergising and disabling the control circuit and permitting free use of the telephone socket for outgoing calls of any kind. In this second position of the cam, the segment 42 of the cam still however blocks access to the mounting screws of the security cover.

A further anticlockwise rotation of the cam 10 through about 450 into a third position can be made by means of the lock 7 to bring the actuating arm 44 of the cam into alignment with the locking tab of the security cover. In this third position, the locking segment 41 of the cam is removed from in front of the locking tab of the security cover 4 and the arm 44 is disposed behind the locking tab so as to enable the security cover to be removed and permit access to the mounting holes 33 normally protected by the security cover. This enables the device to be mounted on or demounted from a telephone socket. In the third position of the cam 10 neither of the indicator elements 47 and 47 is visible in the window 9.

Referring now to Figure 8 of the drawings which shows the control circuit of the device, the control plug 15 and control socket 21 of the device are interconnected by printed conductors 50 and 51 on the printed circuit board, which conductors incorporate respective normally closed contacts 52 and 53 of a relay 54 having a coil 55 which is connected between the positive and negative power rails of the circuit in series with a field effect transistor 56 which controls the current through the relay coil 55.

A signal monitoring circuit is connected to the conductors 50 and 51 and comprises a diode bridge rectifier 58 having a first pair of opposed junctions 59, 60 and a second pair of opposed junctions 61, 62. The junctions 59, 60 are connected respectively to the lines 50 and 52. The junction 61 is connected to the negative terminal of the battery and the junction 62 is connected to the input of a discriminator circuit 63 and to the input of a filtering and switching circuit 64 the operation of which is controlled by the discriminator circuit.

The discriminator circuit 63 has a first signal path connected to the rectifier junction 62 and comprising a diode 66, a Zener diode 67 and a resistor 68 connected in series to one input 69 of a first NAND gate 70, the input 69 of the gate being connected via resistor 71 to the negative power rail. The other input 72 of the gate 70 is connected to the positive power rail. The output of the gate 70 is connected via diode 73 to one input 74 of a second NAND gate 75 having a second input 76. The one input 74 of the second NAND gate 75 is connected to junction 62 of the rectifier 59 via a second signal path comprising a switching field effect transistor 77 and a holding field effect transistor 78.

The gate 79 of transistor 77 is connected firstly to the junction 62 of the rectifier 59 via a series arrangement of a diode 81, a capacitor 82, a diode 83 and a resistor 84 and secondly to the negative rail by a Zener diode 80.. The drain of the transistor 77 is connected to the positive rail and the source to input 74 of gate 75 via oppositely directed diodes 85 and 86 connected in series with the transistor 78. The junction between diodes 85 and 86 is connected to one input 87 of a NOR gate 88 having its second input 89 connected to the negative rail. The output of the gate 88 is connected to the second input 76 of the second NAND gate 75 and also to the gate 90 of the holding transistor 78.The output of second gate 75 is applied to the base 91 of a control transistor 92 having its emitter 93 connected to the negative rail and its collector 94 connected to the base of a switching transistor 95 having its emitter 96 connected to the positive rail and its collector 97 connected to the filtering and switching circuit 66. The control transistor 92 thus renders the switching transistor 95 conductive or non-conductive in dependence upon the output of the second NAND gate 75.

The filtering and switching circuit 64 comprises a first buffer amplifer 100 having its non-inverting input 101 connected to the junction 62 of the rectifier 59 via a capacitor 102 and to the negative rail via a resistor 103. The output of the buffer amplifier is fed back to its non-inverting input 104 and is delivered through capacitor 105 and resistor 106 to the non-inverting input 109 of a second amplifier 110 which is also connected to the negative rail by series connected capacitors 107 and 108. The output of amplifier 110 is fed back to its inverting input 111 and via resistor 112 to the junction of capacitors 106 and 107. The output of amplifier 110 is also supplied via series connected capacitors 114 and 115 to the non-inverting input of a third amplifier 117 which is also connected to the negative rail by resistor 116.The output of the amplifier 117 is fed back to its inverting input 118 and via resistor 119 to the junction of capacitors 114 and 115. The output of amplifier 117 is applied through a resistor 120 to the inverting input 121 of a fourth amplifier 122 having its non-inverting input connected to the negative rail via resistor 123. The output of amplifier 122 is fed back to the inverting input via a feedback network comprising a resistor 124 in parallel with the series arrangement of resistor 125 and diode 126. The output of amplifier 122 is applied via diode 127 to the set input 128 of a first flip flop 129 having a clock input 130 and a Q output 131. The set input 128 of flip flop 129 is connected via capacitor 132 to a negative rail and the clock input 130 is connected to the output 133 of an oscillator 134.The Q output 131 of the flip flop 129 is connected to the clock input 135 of a second flip flop 136 which has its set input 137 connected to the negative rail and its Q output connected to the gate 138 of transistor 56. The flip flop 136 has a reset input 139 connected to the negative rail via parallel paths which respectively include a capacitor 140 and resistor 141. The reset input is further connected to the Q output of flip flop 136 via the series connected resistor 142 and diode 143.

The collector 97 of control transistor 92 is connected to respective power supply inputs 152, 153, 154 and 155, 156 of the first amplifier, the second amplifier, the third amplifier, the oscillator and an integrated circuit 157 containing the first and second flip flop.

In operation of the described circuit with a facsimile machine plugged into the socket 21 of the device and the key 8 turned to the first position to select the call-restricting mode of operation by closing the microswitch 23 and connecting the battery to the control circuit, the fall in line voltage upon dialling a call from the apparatus causes first NAND gate 70 to produce an output to second NAND gate 70 to turn on the transistors 92 and 95, thereby applying the battery voltage to the power inputs of the circuit 66. This starts the oscillator 134 which thereupon applies clock pulses to the clock input of the first flip flop 129. A facsimile carrier signal on the telephone line is applied to the set input 128 of flip flop 129 via the buffer amplifier, the filtering stages 110 and 117 and the amplifier 122 as a D. C. voltage which maintains the set input 128 in a logic high state.Accordingly no output is present on the Q outputs of flip flop 129 and 136, the transistor 56 is off, the relay 54 is de-energised and the apparatus remains connected to the telephone line.

In the absence of continuous facsimile carrier signal, this voltage will not be developed at set input 128 and when the next clock pulse from oscillator 134 is produced, the set input 128 will be in the low logic state, thereby clocking the first flip flop 129 and producing an output signal on its Q output 131 which is applied to the clock input 135 of the second flip flop.

This in turn results in an output signal on the Q output of the second flip flop 136, thereby turning on the transistor 56 so that current flows through the relay coil 55 to open the contacts 52 and 53 and disconnect the apparatus from the telephone line.

In the case of an incoming call with the device in the call-restricting mode, the transistor 77 is turned on by voltage developed by the ringing current, thereby causing the NOR gate 88 to produce an output which is applied to the control terminal 90 of transistor 78 and to the input 76 of NAND gate 75. When a call is accepted, the line voltage falls, NAND gate 70 produces an output, NAND gate 75 thus has a logic high state on both inputs and transistor 78 latches NOR gate 88 with its output in the high logic state, holding the output of NAND gate 75 in the low logic state and maintaining the transistors 92 and 95 off so that the filtering and switching circuit 66 remains de-energised.

When the key 8 is in its second condition, microswitch 23 is open and the battery is disconnected from the control circuit, so that both incoming and outgoing calls are unrestricted.

Claims

CLAIMS:

1. A telephone call control device comprising a casing for attachment to or adjacent to the housing of a freely accessible telephone socket, a control plug carried by the casing for engaging in the telephone socket when the casing is attached, a control socket carried by the casing for receiving the plug of a communications apparatus to be connected to the telephone socket, and control circuit means in the casing for electrically connecting the control socket and the control plug, the control circuit having a call-restricting operating condition in which, following dialling from an apparatus connected to the control socket, the control circuit resistors the transmission on the line and, in the absence of a predetermined carrier, disconnects the line.

2. A call control device according to claim 1, wherein the control device has an unrestricted operating mode in which all incoming and outgoing calls via the telephone socket are permitted.

3. A call control device according to claim 1 or 2, wherein the control circuit comprises a relay controlling contacts in coupling conductors electrically connecting the control socket and the control plug.

4. A call control device according to claim 3, wherein the relay is normally de-energised and the relay contacts are closed.

5. A call control device according to claim 4, wherein the relay is arranged to be energised via switching means which is controlled by filtering means connected to monitor the presence of the predetermined carrier signal on the telephone line after a call has been dialled in the telephone socket.

6. A call control device according to claim 5, wherein the filtering and switching means are normally deenergised and are energised by a discriminator means upon detection of dialling signals from the apparatus.

7. A call control device according to claim 5 or 6, comprising incoming call detecting means for detecting a ringing signal arriving at the telephone socket and maintaining the filtering and switching means deenergised.

8. A call control device according to any preceding claim, wherein the control circuit has a power supply switch which is actuated by the locking means to select the call-restricting operating condition by energising the control circuit.

9. A call control device according to claim 8, wherein the power supply switch is actuated by a rotatable cam controlled by the locking means.

10. A call control device according to claim 9, wherein the casing has a detachable cover which is releasably locked by the rotatable cam and which when released, provides access to mounting means for attaching the device to the telephone socket.

11. A telephone call control device substantially as hereinbefore described with reference to the accompanying drawings.

12. Any novel feature or combination of .features described herein.