GB2273417A

GB2273417A - Telephone line link

Info

Publication number: GB2273417A
Application number: GB9309197A
Authority: GB
Inventors: Yik Sum Terence Fong; Kong Kay Siu; Chun Chiu Laurence Kwan; Wah Hing Cheung
Original assignee: GD SIGNAL Ltd
Current assignee: GD SIGNAL Ltd
Priority date: 1992-12-14
Filing date: 1993-05-05
Publication date: 1994-06-15
Also published as: GB9309197D0

Abstract

A telephone line link for use with each corresponding one of a plurality of telephone sets connected to a common telephone line, which telephone line link (10) comprises a line detector (23) for connection to and detecting the condition of the telephone line, microprocessor-based control means (21) connected to the line detector (23), said control means (21) including memory means for storing a plurality of identification codes for corresponding call recipients, a key-pad (13) connected to the control means (21) for selecting and activating the identification codes, and alerting means (26) controlled by the control means (21) to provide an alert signal for an appropriate call recipient to receive on incoming call in response to an associated identification code detected by the detector (23) through the telephone line. The identification code is issued by the telephone line link (10) of a telephone set initially receiving the call. <IMAGE>

Description

TELEPHONE LINE LINK The present invention relates to a telephone line link suitable for use with each corresponding one of a plurality of telephone sets connected to a common telephone line, in order to render call transfer convenient.

It has become more popular nowadays for a home or domestic premises to have two or more telephone sets provided at different locations or rooms, sharing a single incoming telephone line, for convenience of use. As existing telephone exchange systems, such as PABX systems, are luxurious for household use, the telephone sets are simply wired up together to the telephone line. Call transfer is inconvenient, frequently requiring shouting across rooms.

According to the invention, there is provided a telephone line link for use with each corresponding one of a plurality of telephone sets connected to a common telephone line, which telephone line link comprises a line detector for connection to the telephone line, microprocessor-based control means connected to the line detector, said control means including memory means for storing a plurality of identification codes for corresponding call recipients, a key-pad connected to the control means for selecting and activating the identification codes, and alerting means connected to the control means and adapted to provide an alert signal for an incoming call to alert the appropriate call recipient in response to a corresponding identification code detected by the detector and received through the telephone line from the telephone link of the telephone set receiving the call.

It is preferred that the identification codes are transmitted through the telephone line in pulse form.

Preferably, the identification codes are differentiated by the time separation between two pulses.

In a preferred embodiment, the line detector is a voltage detector adapted to detect the voltage level of the telephone line.

In a specific construction, the line detector comprises a plurality of voltage comparators arranged to determine different threshold voltage levels with which the telephone line voltage is compared.

Advantageously, the alerting means is adapted to provide audible alert signals.

It is preferred that the alert signals are provided according to different ringing patterns.

The telephone line link may further comprise holding means adapted to put the incoming call on hold while the alerting means is in operation.

Preferably, the holding means is adapted to be automatically disabled upon picking up of any one of the telephone sets.

The telephone line link may further comprise indicator means adapted to indicate the condition of the telephone line.

It is preferred that the telephone line link is arranged to be connected to the telephone line electrically in parallel with the telephone set.

The invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a front view of an embodiment of a telephone line link in accordance with the invention; Figure 2 is a side view of the telephone line link of Figure 1; Figure 3 is a rear view of the telephone line link of Figure 1; Figure 4 is a schematic block diagram of an electronic circuitry of the telephone line link of Figure 1; Figure 5 is a detailed circuit diagram of the electronic circuity of Figure 4; and Figure 6 is a waveform diagram of an identification code used by the electronic circuitry of Figure 4.

Referring to Figures 1 to 3 of the drawings, there is shown a telephone line link 10 embodying the invention, which link 10 comprises a elongate two-part casing 11 provided at each end thereof a telephone cord 12. A key-pad consisting of five push-button switches 13 is provided on the front side of the casing 11, together with an LED indicator 14.

On the back of the casing 11, there is a battery compartment 15 for two 1.5V battery cells. The telephone line link 10 is arranged to connect by means of the telephone cords 12 a telephone set to an incoming telephone line.

The telephone line link 10 incorporates an electronic circuitry 20 contained within the casing 11, as shown in Figures 4 and 5. The electronic circuitry 20 includes a microprocessor-based control chip acting as a central processing unit or CPU 21 incorporating a data memory, a bridge rectifier 22 having its pair of input terminals connected to the corresponding leads of each telephone cord 12, and a voltage detector 23 provided between the bridge rectifier 22 and the CPU 21 for detecting the voltage level of the telephone line through the bridge rectifier 22 such that the CPU 21 can monitor the telephone line voltage level. The output of the data memory is fed to the bridge rectifier 22 via a data circuit 24.

The electronic circuitry 20 further includes a hold circuit 25 connected to the bridge rectifier 22 and controlled by the CPU 21, and buzzer and indicator drivers 26 and 27 controlled by the CPU 21. The set of push-button switches 13 is connected to the CPU 21 for selecting and activating the data memory of the CPU 21.

In an existing public telephone system, the domestic telephone line will be at a voltage level of about 48V when the telephone line is idle or when the telephone is on-hook but will drop to about 10V (between 6V and 16V depending on the telephone loading) when the telephone line is engaged by the telephone that being in use or off-hook. Usually, there is a predetermined telephone line threshold voltage level below which the engaging telephone will not be disconnected by the telephone system. The cut-off threshold level is about or slightly above 30V.Depending on the telephone circuitry design, the telephone may clamp the telephone line voltage at a level above the maximum inuse level (16V) but below the cut-off threshold level, thereby holding the telephone line and the other party (generally known as the on-hold state), such that the telephone can perform some other functions including for example call transferring.

The operation of the electronic circuitry 20 is based on a scheme dividing the telephone line voltage level into four modes, namely DATA, IN-USE, ON-HOLD and IDLE modes, as illustrated below with reference to the telephone line voltage level: 0V 5V 18V 26V 48V ±-------±-------------±--------±-------- DATA IN-USE ON-HOLD IDLE According to this scheme, the voltage detector 23 is designed to detect the various operating modes of the telephone line by incorporating a reference potential divider formed by a series circuit of resistors R4, R15, R16 and R17 and three op-amp voltage comparators U2A, U2B and U2C connected at their negative terminals to the respective junctions of the resistors, corresponding to the telephone line voltage at 26V, 18V and 5V. The output terminals of the voltage comparators are connected to the corresponding pins of the CPU 21. The telephone line voltage is picked up by means of the bridge rectifier 22 and is stepped down by an input potential divider formed by resistors R2 and R3 and is then fed to the positive terminals of voltage comparators such that the reference potential divider can operate on the battery level of 3V.

In a telephone system where several telephone sets share a single incoming telephone line, one such telephone line link 10 is used to be connected physically in series between each telephone set and the telephone line. The principle function of the telephone line link 10 is to enable the initial call recipient at a particular telephone set to alert, when the telephone call is not for himself, the appropriate recipient by pressing the designated pushbutton switch 13 on the link casing 11, by means of which an associated ringing signal will be emitted by all the other four telephone line links 10 until the right recipient recognises the ringing signal and picks up the handset of any one of the other telephone sets that is convenient to him.

The data memory of each telephone line link 10 is arranged to store five different identification codes which are associated with the respective push-button switches 13 and corresponding to a maximum number of five users of the telephone sets in the same premises. When a particular push-button switch 13 of a telephone line link 10 is pressed by the initial call recipient while the telephone line is in the IN-USE mode (5V to 18V), the local CPU 21 will provide a data signal (identification code) on the telephone line by means of the data circuit 24. The data circuit 24 is essentially a transistor switching circuit operative to draw down the telephone line voltage level appearing at the bridge rectifier 22 from 5V-18V (IN-USE mode) to below 5V (DATA mode) and at about 3V, momentarily for 15ms twice, thereby producing a series of two inverted pulses as shown in Figure 6.The time separation between the two pulses, denoted by T, is predetermined to be different from one data signal to another.

As all the telephone line links 10 are connected to the same telephone line, the generated data signal will be transmitted to and detected by all the other telephone line links 10 (except the one generating the data signal) by their CPU's 21 by means of the corresponding voltage detectors 23 via the respective bridge rectifiers 22 from the telephone line. Upon receipt of this data signal, the CPU's 21 will control the corresponding buzzer drivers 26 and buzzers to generate a particular ringing signal to alert the other users in the premises.

The five ringing signals are designed to be easily distinguishable one from another, and they are in this particular example arranged according to the following beep patterns: a) beeeeeeeeeeeeeep...................beeeeeeeeeeeeeep.....

b) beeeeep..beeeeep...................beeeeep..beeeeep.....

c) beep..beep..beep...................beep..beep..beep.....

d) beeeeeeeee..beep...................beeeeeeeep..beep.....

e) beeeeep..beep..beep................beeeeep..beep..beep..

In the situation where call transfer is required, the initial call recipient presses an appropriate push-button switch 13 and then puts down the handset. As soon as the appropriate button 13 is pressed, the CPU 21 detects this and in response will put the hold circuit 25 ready. After the handset is put down, the hold circuit 25 is activated so as to clamp the telephone line voltage at about 21V and to generate music onto the telephone line.

The hold circuit 25 includes a pair of cascaded transistors Q5 and Q6 connected in series with a resistor R9 and two zener diodes ZN1 and ZN2, with the base terminal of the pair of cascaded transistors Q5 and Q6 controlled by the CPU 21. The transistors Q5 and Q6 are turned on in order to put the hold circuit 25 ready, but at this time the hold circuit 25 is not yet activated as the line voltage remains at the IN-USE mode. When the handset is put down, the telephone line voltage jumps and then is clamped by the two zener diodes ZN1 and ZN2 at about 21V. As a result, the telephone call is put on-hold while the appropriate ringing signal is rung at all the other telephone line links 10.

The hold circuit 25 further includes a music generating chip U3 which is activated at the same time as the telephone line voltage jumps to the ON-HOLD mode, thereby providing a segment of music to the calling party while he is waiting for the appropriate call recipient to come. It is understood that the music level on the telephone line remains in the range of 18V to 26V (ON-HOLD mode).

Upon picking up of the handset of any one of all the telephone sets, the telephone line will be engaged again and its voltage level will be drawn back down to between 5V and 18V (IN-USE mode). Such a line voltage change will be detected by the CPU 21 of the holding telephone line link 10 by means of its voltage detector 23, and in response the CPU 21 deactivates the hold circuit 25 in action, by sending a logic low signal to the cascaded transistors Q5 and Q6. The disabling of the hold circuit 25 is also effected by the drop of telephone line voltage to below the breakdown level of the zener diodes ZN1.

It is understood that when the second call recipient finishes using the telephone, he may put down the handset to terminate the telephone call or may alternatively transfer the call to a third user by making use of the telephone line link system, repeating the same operation as described above.

Each indicator driver 27 serves to drive the LED 14 to indicate the operating mode of the telephone line, under the control of the associated CPU 21, for example by the LED being turned continuously on to indicate telephone line busy, flashing rapidly to indicate the presence of an incoming call, and flashing slowly during call transfer.

Telephone conference at the near end of the telephone line is possible by the call recipient inviting a second user in the same premises by means of the telephone line link system in the same manner as described above, to use another telephone set, except that the first user should not hang up.

Inter-communication is also possible by making use of the telephone line link system in the same manner as described above, in the absence of an incoming telephone call.

It is to be appreciated that the telephone cords 12 are connecting the telephone set directly to the telephone line and that the telephone line link circuitry 20 is connected electrically in parallel across the two leads of each of the two telephone cords. This arrangement enables the circuitry 20 to stay totally idle when it is not in operation, either when the telephone sets are not in use or during telephone conversation, thereby being power saving.

It is envisaged that the data signals (identification codes) may be distinguished one from another by reference to the pulse width or pulse number or may be in tone form differentiated by frequency.

It is appreciated that the telephone line link may be incorporated as an integral part of a telephone set.

It is also appreciated that such a built-in telephone line link may share the existing dialling key-pad of the telephone set. With this design, an additional key or one of the existing function keys may be assigned for switching the key-pad to the telephone line link, or alternatively time-multiplexing scheme may be employed for the sharing of the key-pad.

In connection with pulse dialling telephones, the dialling pulse trains generated by the key-pad itself may be used as the data signals for the telephone line links to identify the users. In this arrangement, the CPU's of the telephone line link control circuitries are programmed to count the number of pulses of the transmitted or distributed data signal in order to select a corresponding ringing signal to alert the users.

It is further envisaged that the telephone line link may be used with terminal equipment other than telephones, such as facsimile machines, answering machines and voice mail systems.

The invention has been given by way of example only, and various other modifications of and/or alterations to the described embodiment may be made by persons skilled in the art without departing from the scope of the invention as specified in the appended claims.

Claims

1. A telephone line link for use with each corresponding one of a plurality of telephone sets connected to a common telephone line, which telephone link comprises a line detector for connection to and detecting the condition of the telephone line, microprocessor-based control means connected to the line detector, said control means including memory means for storing a plurality of identification codes for corresponding call recipients, a key-pad connected to the control means for selecting and activating the identification codes, and alerting means controlled by the control means to provide an alert signal for an appropriate call recipient to receive an incoming call in response to an associated identification code detected by the detector through the telephone line, said identification code being issued by the telephone line link of a telephone set initially receiving the call.

2. A telephone line link as claimed in claim 1, wherein the identification codes are transmitted through the telephone line in pulse coded form.

3. A telephone line link as claimed in claim 2, wherein the identification codes are differentiated by the time and/or pulse duration separation between two pulses.

4. A telephone line link as claimed in any one of claim 1 to claim 3, wherein the line detector is a voltage detector adapted to detect the voltage level of the telephone line.

5. A telephone line link as claimed in claim 4, wherein the line detector comprises a plurality of voltage comparators arranged to determine different threshold voltage levels with which the telephone line voltage is compared.

6. A telephone line link as claimed in any one of the preceding claims, wherein the alerting means is adapted to provide audible alert signals.

7. A telephone line link as claimed in claim 6, wherein the alert signals are provided according to different ringing patterns.

8. A telephone line link as claimed in any one of the preceding claims, further comprising holding means adapted to put the incoming call on hold while the alerting means is in operation.

9. A telephone line link as claimed in claim 8, wherein the holding means is adapted to be automatically disabled upon picking up of any one of the telephone sets.

10. A telephone line link as claimed in any one of the preceding claims, further comprising indicator means adapted to indicate the condition of the telephone line.

11. A telephone line link as claimed in any one of the preceding claims, being arranged to be connected to the telephone line electrically in parallel with the telephone set.

12. A telephone line link for use with each corresponding one of a plurality of telephone sets connected to a common telephone line, substantially as hereinbefore described with reference to the accompanying drawings.

Amendments to the claims have been filed as follows 1. A telephone line link for use with each corresponding one of a plurality of telephone sets connected to a common telephone line, which telephone link comprises a line detector for connection to and detecting the condition of the telephone line, microprocessor-based control means connected to the line detector, said control means including memory means for storing a plurality of identification codes for corresponding call recipients, a key-pad connected to the control means for selecting and activating the identification codes, and alerting means controlled by the control means to provide an alert signal for an appropriate call recipient to receive an incoming call in response to an associated identification code detected by the detector through the telephone line, said identification code being issued by the telephone line link of a telephone set initially receiving the call.

13. A telephone set incorporating a telephone line link as claimed in any one of the preceding claims.

14. A telephone set as claimed in claim 13, including a dialling key-pad which serves also to provide the key-pad of the telephone line link.