GB2214384A - A control system for use with a telephone system - Google Patents

Abstract

A control system (10) for the remote control of an apparatus (16) by a remote telephone of a telephone system using loop-disconnect signalling, comprises a switch (11), a receiver (12), a filter (13) and a detector (14). The receiver (12) couples a telephone line (15) of the telephone system with the filter (13) of the control system (10) when receiving a ringing signal from the telephone line (15), and subsequently receives a control code signal from the telephone line (15) when the latter is coupled. The filter (13) extracts and transforms the control code signal into digital pulse form. The detector (14) acknowledges the control code signal to provide a control signal to the apparatus (16). <IMAGE>

Description

A CONTROL SYSTEM FOR USE WITH A TELEPHONE SYSTEM The present invention relates to a control system for use with a telephone system.

According to the invention there is provided a control system for the remote control of an apparatus by a remote telephone of a telephone system using loop-disconnect signalling, the control system comprising a receiver for coupling to a telephone line of the telephone system to receive a signal placed on the line from the remote telephone, a filter for detecting a loop-disconnect signal corresponding to a dialling digit on the line and transforming the signal into digital pulse form, and a detector for detecting the transformed signal and issuing a command signal to a said apparatus.

The system is particularly suitable for use in a "No Disturb Telephone System". The system is coupled with a user's telephone so that the telephone is not responsive to a telephone call until the control code is received, whereupon the telephone will ring and operate in the usual way.

The invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a block-diagram representation of a control system embodying the invention; Figure 2 is a more detailed block-diagram representation of the control system of Figure 1; Figure 3 is a circuit diagram showing a practical implementation of the control system of Figure 2; Figure 4 shows signal waveforms in a filter of the control system of Figure 3; and Figure 5 shows apparatus for connecting the control system of Figures 1 to 3 to a telephone.

Referring to Figure 1 of the drawings, a control system 10 in accordance with the invention comprises a switch 11, a receiver 12, a filter 13 and a detector 14. The receiver 12 has an input connected to a telephone line 15. The receiver 12 triggers the switch 11 on detection of a ringing signal on the telephone line 15, and the switch 11 subsequently triggers the receiver 12 to couple the telephone line 15 with the filter 13, supplies electrical power from a power source (not shown) to the filter 13 and detector 14, and sends a reset signal to the detector 14.

The filter 13 eliminates any undesirable signals or noise from a control code signal (vide hereinafter) received from the telephone line 15. The control code signal is passed by the filter 13 to the detector 14 which is presettable to detect a particular control code. The detector 14 is also connected to and for controlling an apparatus 16.

In operation, a calling user produces, by means of a remote telephone, a ringing signal on the telephone line 15. It will be appreciated that the control system 10 may be coupled to the telephone line 15 in parallel with a telephone handset or in place of the handset. When receiving the ringing signal, the receiver 12 triggers the switch 11 to deliver power to the filter 13 and the detector 14, and couples the telephone line 15 with the filter 13. The calling user then sends a control code signal through the telephone line 15 to the detector 14 via the filter 13. The filter 13 separates the control code signal from any undesirable signals or noise appearing on the telephone line 15, and transforms the control code signal into digital pulse form.When the received control code is coincident with a preset code in the detector 14, the detector 14 sends an output signal to control the apparatus 16, for example to turn on the apparatus 16.

Referring now to Figures 2 and 3 of the drawings, the switch 11 comprises a supply regulator 17, a hang-up signal detector 18, a power control timer 19, a power delay timer 20 and a reset control 21. The receiver 12 comprises a ringing signal detector 22 and a line coupler 23.

The power control timer 19 controls the operation of the reset control 21 via the power delay timer 20 which provides a time delay of, say, 15 to 20 seconds to the operation of the control timer 19. This time delay allows the calling user at the remote end of the telephone line 15 to receive a bell signal confirming his call. After the time delay, the reset control 21 activates the line coupler 23 to couple the telephone line 15 with the filter 13, and simultaneously resets the decoder 14 (vide hereinafter).

To maintain the operation of the supply regulator l7 after the telephone line 15 is coupled and the ringing signal is no longer present, the power control timer 19 sends via the delay timer 20 an enabling signal to the regulator 17. The control timer 19 also limits the overall operating time of the control system 10 to, say, 251 to 30 minutes by inhibiting the enabling signal to turn off the regulator 17. This time limit prevents any prolonged engagement of the telephone line 15. The hang-up signal detector 18 disables the control timer 19 when detecting a hang-up signal on the telephone line 15 via the line coupler 23, which will again turn off the regulator 17.

The operation of the filter 13 will now be described. The filter 13 comprises a noise discriminator 24 and a pulse processor 25 for eliminating any undesirable signals or noise received from the telephone line 15, and transforming the control code signal which is sent down the telephone line 15 into digital pulse form.

The control code signal is generated at the remote telephone by pressing or dialling the appropriate digit(s) after the bell signal confirming the call has been received. The signal received by the receiver 12 may comprise, for example, the control code which is shown as a dialling digit of "5", a clicking noise and background noise. The received signal waveform is shown in Figure 4(a). The clicking noise may originate from a telephone switching station, or may be picked up by the telephone line 15 by interference. The background noise comes from the calling user's environment by, for example speech, television or radio.

The frequency band of a telephone line is typically 300Hz to 3.4kHz suitable for speech transmission. When a square signal is transmitted through the telephone line, the frequency components outside of this range will be filtered out. Consequently, the control signal of figure 4(i) when transmitted through the telephone line 15 will appear as shown in Figure 4(a), the control code and the clicking noise being in the form of tone/signal bursts.

Each tone burst corresponds to an abrupt edge of the control code pulses and the clicking noise pulses, and has a sharp rising edge. The background noise consisting mainly of speech signal or the like will remain substantially undistorted, having a slow rising amplitude profile.

Figures 4(a) to 4(f) show the signal waveforms at corresponding circuit points A to F of the filter 13 shown in Figure 3. To distinguish the control code from the noises, the difference in amplitude profiles is made use of. The noise discriminator 24 comprises a high level detector 26, a low level detector 27, a rising edge detector 28 and a time shift comparator 29. The high level detector 26 detects the duration of a certain comparatively high level amplitude of the telephone line signal bursts, whilst the low level detector 27 detects that of a certain low level amplitude of the signal bursts, the latter duration being substantially the duration of the signal burst. The output waveforms of the detectors 26 and 27 are shown in Figures 4(b) and 4(c).

The rising edge detector 28 detects rising edges of the output of the low level detector 27 to facilitate the operation of the time shift comparator 29. The output waveform of the rising edge detector 28 is shown in Figure 4(d).

For each signal burst of the control code and the clicking noise, the output pulses of the two detectors 26, 27 occur substantially at the same time instant because of the sharp rising edges, whilst for the background noise, the corresponding output pulses occur at separate time instants because of the low rising amplitude profile. The time shift comparator 29 detects the difference in timing of the pulses in the waveforms 4(b), 4(c), and outputs a pulse when the difference in time is less than a predeterminded amount. Each time comparison cycle of the comparator 29 is initiated by a rising edge of the output pulses of the detector 28, and terminated by the trailing edge of the pulses. The output waveform of the time shift comparator 29 is shown in Figure 4(e), from which it can be seen that the background noise has been eliminated.

The pulse processor 25 is a frequency divider having a division factor of two. Each division cycle is initiated by a pulse appearing at the input of the pulse processor 25, and a pulse is produced on the occurrence of a second pulse at the input within a predetermined time interval, or the processor 25 resets at the end of the time interval in the absence of a second pulse.

Each control code pulse Figure 4(i)] has a duration long enough to cause it to appear at the receiving end of the telephone line 15 as two distinct signal bursts, and hence two distinct pulses at the output of the time shift comparator 29. However, the clicking noise pulse has a very short duration and hence the two signal bursts at the telephone line receiving end (due to the rising and falling edges) overlap, and so only a single pulse is produced at the comparator output [Figure 4(e)).

Consequently, interference by the clicking noise is eliminated by the pulse processor 25, the output waveform being shown in Figure 4(f). Figure 4(f) when compared with Figure 4(i) shows that only the control code among the telephone line signals on the telephone line 15 passes through the filter 13, and this is regenerated into digital pulse form.

The control code [Figure 4(f)] is fed to the detector 14.

For security reasons it is preferable to use an at least two digit control code, and a system for using this is described. To accept a two dialling digit control code, the detector 14 of the control system 10 shown in Figure 3 comprises two presettable decimal counters 30, 31, a counter selector 32 and an output delay timer 34. The counter selector 32 sequentially enables the two counters 30, 31 to receive respective digits of the control code from the pulse processor 25. Each of the two counters 30, 31 provides a logic "1" output to a logic NAND gate 33 when the received control code digit coincides with its preset value, or else a logic "0" output. The NAND gate 33 sends an enabling signal to the output delay timer 34 when the two counters 30, 31 receive respective correct control code digits.

The two counters 30, 31 are serial input shift counters each having ten modified output pins corresponding to decimal dialling digits "1" to "9" and "0". Before receiving the control code when the control system 10 starts to operate, the two counters 30, 31 are reset by the reset control 21 so that none of the output pins is enabled. The reset control 21 simultaneously resets the counter selector 32 to enable the first counter 30 to receive the first control code digit. The first counter 30 enables its output pins sequentially from "1" onwards until the complete pulse train of the first digit has been received, leaving only the output pin corresponding to the control code digit enabled. For example, when the digit "5" is received, pin 1 goes high on receiving the first pulse. On receiving the second pulse, pin 1 goes low, and pin 2 goes high, and so on.A presettable selector switch 30' is provided to connect a selected output pin of the counter 30 to the input of the NAND gate 33 and hence select the control code. Hence the counter 30 sends a logic "1" output to the NAND gate 33 only when the selected output pin is enabled by receiving a corresponding control code digit.

After receiving a complete first control code digit pulse train, the counter selector 32 selects the second counter 31 to receive the second control code digit. The selector 32 comprises a timer for detecting the time interval between the receipt of pulses. When this time interval exceeds a predetermined valve, the selector assumes that the digit is finished and so selects the second counter 31. The second counter 31 has a presettable selector switch 31' and operates in the same manner as the first counter 30 does. After the complete second digit is received, the counter selector 32 enables the output delay timer 34 and inhibits the two counters 30,31.

The output delay timer 34 triggers a muting circuit 35 and the apparatus 16 after a short time delay of, say, one second in response to an enabling signal received from the NAND gate 33. This time delay is provided to ensure the second counter 31 receives the complete second control code digit pulse train before the muting circuit 35 and the apparatus 16 are triggered. Otherwise, premature triggering may occur when the second control code digit pulse train is longer than the one preset, i.e. the second counter 31 is temporarily triggered as the output pins. are cycled through, which temporarily gives an enabling output.

In a particularly preferred embodiment, the apparatus 16 to be controlled by the control system 10 is a telephone 16' having a bell signal generator 36 and a piezo-electric buzzer 37. The bell signal generator 36 is formed by a pair of low frequency oscillators 38 and a high frequency oscillator 39 for generating a bell signal consisting of separate pairs of high frequency signal bursts, as generally known in the art.

To enable the calling user at the remote end of the telephone line 15 to confirm that a correct control code is dialled, an answer back generator 40 is provided to transmit the bell signal given by the buzzer 37 via the line coupler 23 and the telephone line 15 to the calling user. The muting circuit 35 mutes an input channel of the line coupler 23 to prevent any background noise from entering into the telephone line 15 at the calling user end when the answer back bell signal is being transmitted.

Figure 5(a) shows a telephone 16' comprising a telephone circuit 41, a handset 42, a bell circuit 43, and a switch 44 operable by the handset 42 to connect either the telephone circuit 41 or the bell circuit 43 to the telephone line 15. In use, the control system 10 and a separate bell circuit 45 comprising the muting circuit 35, the bell signal generator 36, the buzzer 37 and the answer back generator 40 are connected by a manual switch 46 to the telephone 16', as shown in Figure 5(b).

In operation, with the two switches 44, 46 in respective positions as shown in Figure 5(b), the control system 10 receives a ringing signal from the telephone line 15. The line coupler 23 operates after 15 and 20 seconds to couple the telephone line 15 with the filter 13 of the control system 10, and the calling user is notified accordingly by the absence of the ringing signal from the telephone line 15. The calling user then dials the two digit control code, and subsequently receives an answer back bell signal given by the bell circuit 45 when the control code is acknowledged by the detector 14. The bell signal also alerts a user of the telephone 16' who then picks up the handset 42 to connect the telephone line 15 to the telephone circuit 41 to answer the telephone call.The control system 10 may be bypassed by means of the switch 46 so that the telephone set 16' operates as usual with the internal bell circuit 43.

The telephone 16' when combined with the control system 10 constitutes to a "No Disturb Telephone System" with which a user may select so as to receive telephone calls only from persons to whom the preset control code has been given.

The control system as hereinbefore described is not limited to use for controlling a telephone. It may also be used to control remotely any other apparatus, such as a video tape recorder, through commercial telephone lines.

Furthermore, the control system may have a paralled circuit of detectors 14 presettable with different control codes for controlling more than one apparatus.

The invention is given by way of example only and various improvements and/or modifications may be made without departing from the scope of the invention defined by the appended claims.

Claims (14)

1. A control system for the remote control of an apparatus by a remote telephone of a telephone system using loop-disconnect signalling, the control system comprising a receiver for coupling to a telephone line of the telephone system to receive a signal placed on the line from the remote telephone, a filter for detecting a loop-disconnect signal corresponding to a dialling digit on the line and transforming the signal into digital pulse form, and a detector for detecting the transformed signal and issuing a command signal to a said apparatus.

2. A control system as claimed in claim 1, wherein the filter comprises pulse detecting means for detecting the pulses of the loop-disconnect signal and means for generating a digital signal corresponding to the loop-disconnect signal.

3. A control system as claimed in claim 2, wherein the pulse detecting means comprises means for detecting on the line signal bursts corresponding to the start and finish of each pulse of the loop-disconnect signal transmitted by the remote telephone.

4. A control system as claimed in claim 3, wherein the pulse detecting means comprises first amplitude detecting means for detecting when a signal on the telephone line exceeds a predetermind low level of amplitude, second amplitude detecting means for detecting when a signal on the telephone line exceeds a predetermind high level of amplitude, first timer means for indicating when the signal exceeds the low and high levels of amplitude within a first predetermind time interval.

5. A control system as claimed in claim 4, wherein the pulse detecting means further comprises second timer means for detecting when the signal exceeds twice within a second predetermined time interval the low and high levels of amplitude within the first predetermined time interval within a second predetermined time interval.

6. A control system as claimed in any one of claims 1 to 5, wherein the transformed signal detector comprises a presettable counter for counting the number of digital pulses of the transformed signal and provides a command signal on receiving a number of pulses equal to the count preset in the counter.

7. A control system as claimed in claim 6, wherein two presettable counters are provided to detect respective digits.

8. A control system as claimed in any one of the preceding claims, further comprising means for generating an alert signal in response to the command signal provided by the detector.

9. A control system as claimed in claim 8, further comprising means for transmitting an acknowledgement signal to the remote telephone.

10. A telephone incorporating a control system as claimed in any one of the preceding claims.

11. A no disturb system for a telephone, comprising means for receiving a call from a remote telephone, means for detecting a code signal placed on the telephone line by means of the remote telephone, and means for activating the telephone on receipt of the code signal.

12. A control system as hereinbefore described with reference to the accompanying drawings.

13. A telephone as hereinbefore described with referece to the accompanying drawings.

14. A no disturb system for a telephone as hereinbefore described with reference to the accompanying drawings.