GB2245800A - Telephone instrument - Google Patents

Abstract

In a telephone instrument the absence of transmitted speech is detected at 14 when the instrument is in its off-hook condition. After a preset delay the instrument is switched to its on-hook condition by opening of S2. This prevents unnecessary use of exchange equipment e.g. at the end of a call when the handset is incorrectly replaced. <IMAGE>

Description

TELEPHONE INSTRUMENT This invention relates to telephone equipment, and in particular to a telephone subscriber's instrument.

A conventional telephone subscriber's instrument comprises a subset and handset combination which is connected to the line by removal of the handset from the subset thereby activating a hook-switch. A particular problem experiences with the use of suc: instrument is that it may inadvertently be left in its off-hook condition e.g. by disturbance or incorrect replacement of the handset. In such circumstances ne instrument becomes or remains connected to the exchange via the subscriber loop.This not only prevents the subscriber from receiving further cells, as the line appears to the exchange to be busy, but can aiso in some circumstances result in continuation of subscriber billing for the most recently connected call made from the instrument. Furthermore, when the instrument is in its off-hook condition with no call in progress, this represents an unnecessary use 0 exchange equipment and limits the capacity of the exchange to service calls from other subscribers.

The object of the invention is to minim-se or to overcome this disadvantage.

According to the invention there is provided a telephone subscribers instrument, including means for detecting the transmission of audio signals from the instrument to the line when the instrument is in its off-hook condition, and for disconnecting the instrument from the line after a predetermined delay in the absence of a transmitted audio signal.

According to the invention there is further provided a telephone subscriber's instrument, including a subset and an associated handset, a hook-switch operable upon removal of the handset from the subset, further switch means associated with the hook-switch, means operable when the handset is off-hook for detecting the presence of audio signals in the transmission path from the instrument to the line, and means responsive to the detector means for controlling the further switch means whereby to return the instrument to an on-hook condition in the absence of the audio signals after a predetermined delay.

According to the invention there is further provided a telephone subscriber's instrument including a subset and an associated handset, a hook-switch operable upon removal of te handset from the subset, control means enabled by operation of the hook-switch, a further switch controlled via the control means upon operation of the hook-switch and whereby line current is drawn to effect a call, means operable when the handset is off-hook for detecting the presence of audio signals in the transinisslon path fron the instrument to the line and timer means associated with the control means, te arrangement being such that in the absence, during a call, of transmitted audio signals for a perIod detered by the timer means, the control means opens the further switch whereby to terminate the call and return the instrument to an on-hook condition.

An embodiment of the invention will now be described with reference to the accompanying drawing in which the single figure is a schematic diagram of the subset circuitry of a telephone subscriber's instrument.

Referring to the drawings, the subscriber's instrument is coupled to the line L via a rectifier bridge 11 whereby a current supply polarity to the instrument is ensured. The instrument is coupled to the line via a hook-switch S1 which is closed by lifting of a handset (not shown). Optionally, a push-button switch PB1 is arranged in parallel with the hook-switch e.g. to provide a hands-free function where the instrument is to be employed in a loudspeaking mode. Both the hook-switch S1 and the push-button switch PB1 are coupled between the bridge output and control/timer circuit 12. A further, electronic hook-switch S2 controlled by the control/timer circuit 12 is coupled between the bridge 11 and the speech circuitry of - instrument.Typically the push-button switch is of the push-to-make, push-to-release type. Alternatively, the push-button switch XB1 may be of the momentary contact type, the control circuit 11 then being arranged to latch the switch S2 to its closed condition. In the hands-free model the switch S2 may then be released e.g.

by momentary removal and replacement of the handset.

The instrument speech circuitry includes a two-wire to four-wire transmission circuit 13 coupled to the line L via the bridge 11 and the switch S2 and via which audio signals are transmitted to a receiver transducer RX and from a transmitter transducer TX. A noise monitor/speech detector circuit 1 is interfaced between the transmitter transducer TX and the transmission circuit i3.

Operation of te instrument is controlled by the control and timer circuit 11 coupled to the speech detector circuit 13 and to the electronic hook-switch S2. The control and timer circuit 14 is also provided with an input from a keypad 11 whereby signalling of a dialled number to the exchange via the line may be effected. If loop-disconnect dialling is employed, this may be effected by control of the electronic hook-switch S2 to provide the appropriate break impulses to the line. The control circuit 11 has a reset input activated upon operation of the hook-switch S1 whereby the circuit timer is reset to zero. A second reset input is activated by operation of the push-button switch PB1.

The operation of the instrument follows the following sequence. On lifting the handset (not shown) the hook-switch S1 closes connecting the control circuit 11 to the line and resetting the timer of the control circuit 11. The electronic hook-switch S2 is then held in its closed condition by the control circuit. Closure of the switch S2 results in current being drawn from the line thus indicating to the exchange that a connection is to be made.

Whilst a call is in progress the speed detector 14 monitors traffic on the path between the transmitter transducer TX and the two-wire to four-wire circuit 13. Whenever audio traffic is detected, te speech detector 14 sends a signal to the control cIrcuit 11 whereby the timer of that circuit is reset to zero.

If no transmitted audio traffic is detected, the tier of the control circuit 11 is not reset. After a predetermined time period, e.g. 1 to 5 minutes, during which no audio traffic has been detected, the control circuit 11 opens the electronic hook-switch S2 thus dIsconnecting the instrument speech circuits from the line and causing release of the line at the exchange.

The electronic hook-switch remains in its open condition until the instrument hook-switch has been opened and reclosed, e.g. by correct replacement followed by removal of the handset.

In some applications a user-operable control (not shown) may be provided to temporarily disable the disconnection function, e.g. to allow the caller to listen to a pre-recorded announcement or to hold a line open whilst awaiting a particular called party.

Claims (7)

1. A telephone subscriber's instrument, including means for detecting the transmission of audio signals from the instrument to the line when the instrument is in its off-hook condition, and for disconnecting the instrument from the line after a predetermined delay in the absence of a transmitted audio signal.

2. A telephone subscriber's instrument, including a subset and an associated handset, a hook-switch operable upon removal of the handset from the subset, further switch means associated with the hook-switch, means operable when the handset is off-hook for detecting the presence of audio signals in the transmission path from the instrument to the line, and means responsive to the detector means for controlling the further switch means whereby to return the instrument to its on-hook condition in the absence of the audio signals after a predetermined delay.

3. A telephone subscriber's instrument including a subset and an associated handset, a hook-sw tch operable upon removal of the handset from the subset, control means enabled by operation of the hook-switch, a further switch controlled via the control means upon operation of the hook-switch and whereby line current is drawn to effect a call, means operable when the handset is off-hook for detecting the presence of audio signals in the transmission path from the instrument to the line, and timer means associated with the control means, the arrangement being such that, in the absence, drink a call, of transmitted audio signals for a period determined by the timer means, the control means ope-.s the further switch whereby to terminate the call and return the instrument to an on-hook condition.

4. An instrument as claimed ln claim 2 or 3, wherein a further, push-button switch is provided in parallel with the hook-switch whereby to provide hands-free operation.

5. An instrument as claimed in claim 2, 3 or 4, wherein the further switch is operable via the control means whereby to provide loop-disconnect signals of dial impulses to an exchange.

6. A telephone subscriber's instrument substantially as described herein with reference to and as shown in the accompanying drawing.

7. A telephone system provided with a plurality of subscriber's instruments as claimed in any one of claims 1 to 6.