GB2116807A

GB2116807A - Remote switching unit

Info

Publication number: GB2116807A
Application number: GB08206276A
Authority: GB
Inventors: John Roger Kerfoot Hughes
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-03-03
Filing date: 1982-03-03
Publication date: 1983-09-28
Also published as: GB2116807B

Abstract

Apparatus for remotely controlling an electrical circuit via a telephone network has a first relay operable to simulate an off-hook condition when a ringing signal is received, a timer which is actuated when the off-hook condition is established, and an output relay for switching the electrical circuit in response to the apparatus remaining connected to a calling telephone for longer than a predetermined period. The apparatus includes a tone generator for indicating the state of the output relay to the caller. Disconnection of the calling telephone is detected by sensing the dialling tone. Switching of the electrical circuit therefore only occurs if the caller waits until the tone transmitted by the tone generator indicates that the circuit has been switched.

Description

SPECIFICATION Remote switching unit This invention relates to a switching unit for the remote switching of an electrical circuit by means of the telephone network.

The remote control of circuits by a switching device connected to a telephone line is known. In a number of such known devices the ringing signal transmitted by the exchange is detected and then the caller is required to produce a predetermined sound such as a whistle with a certain frequency range in order to cause the switching device to respond. The device may be connected for example to a central heating system in a home so that the house can be heated some time prior to the caller's arrival by telephoning from the remote location.

It is an object of this invention to provide a switching unit which does not require the caller to produce a sound signal by whistling or with a pocket "bleeper" in order to perform the switching operation.

According to this invention there is provided a switching unit for the remote switching of an electrical circuit by means of the telephone network, the unit comprising switch means in the electrical circuit responsive to an incoming call to open or close the circuit, the switching action being dependent on the instant at which the handset of the calling telephone is replaced. The unit may include detector circuit operable to sense the presence of the dialling tone transmitted by the exchange when the handset of the calling telephone is replaced. Preferably the unit transmits a tone signal indicative of the state of the circuit to be switched so that the caller can relatively easily determine the moment at which the handset should be replaced, the unit being adapted to perform a switching operation only if the caller waits for a predetermined time interval before hanging up.

A preferred embodiment of the invention will now be described with reference to the drawings in which Figs. 1 and 2 are circuit diagrams of a switching unit in accordance with the invention.

Referring to Fig. 1, the apparatus includes a circuit arrangement 1 for interfacing appliance switching circuitry with the telephone line 2 and for detecting a ringing signal transmitted from the telephone exchange. The arrangement 1 is adapted to present impedances to the line which are similar to those exhibited by a standard telephoning during on-hook and off-hook conditions. The ringing signal comprises a 1 7 Hz a.c. signal transmitted in bursts. When simulating the on-hook condition, the relay RLA de-energised and contacts RLA2 are open and the line is open-circuited to d.c. When the ringing signal is transmitted, C2 charges progressively via C, and D, until the voltage on C2 reaches a level sufficient to switch transistor TR2 on. Transistor TR, is normally off.If the ringing signal stops before the required level is reached C2 discharges slowly via R3 so that the circuit is reset. The time taken to reach the required level can be adjusted to deter other callers by choosing suitable values for R1, R2, R3 and C2. Transistor TR2 energises the relay RLA and is latched on by the closing of contacts RLA,. Contacts RLA2 close to connect R7 and transformer T, to the line. R7 is chosen to simulate the microphone impedance of the normal telephone.

By detecting the ringing signal, the relay RLA is caused to connect a d.c. circuit across the line and to generate a START signal whose function will be described below. The exchange will therefore detect an off-hook condition and connect the caller to the line and thus also to the transformer T,. A tone signal, indicating the state of an appliance connected to the apparatus, is fed via C3 and R9 to'the transformer T, and is heard by the caller.

Should the caller hang up, the dialling tone transmitted by the exchange is amplified by an amplifier A1, and detected by a bandpass filter F, tuned to the dialling tone frequency and a comparator CP1, producing a positive edge dial tone signal DS.

The START signal is fed to the appliance sitching circuitry shown in Fig. 2. It is first inverted and then used to trigger a first integrated circuit timer TM, which has been connected to produce a negative-going 30 second pulse when triggered. The trailing edge of this pulse is in turn used to trigger a similar timer TM2 connected to produce a negative-going 10 second pulse at its output. The end of the 10 second pulse is detected by the differentiating and rectifying arrangement of D2, C4 and D3, the resulting positive spike being fed to a schmitt trigger ciruit ST, to activate a flip-flop circuit FF,. As a result of the flip-flop circuit FF, changing state, TR4 also changes state to operate a second rely RLB whose contacts RLB, and RLB2 move to either connect or disconnect the appliance to or from the mains supply.If the appliance was on (flip-flop output Q high) then the end of the ten-second pulse will cause the flip-flop to change state (Q low) and turn the appliance off. The reverse happens if the appliance was originally off. The same change of state can be produced manually by operating a push switch S,.

The choice of a 30 second period followed by a 10 second period means that the caller must wait 40 seconds before replacing his handset if he wishes the appliance to be switched. If on the other hand he does not wish to switch the appliance he must replace the handset before the end of the 40 second period. This results in the dial tone signal DS being generated and fed to TR3 which immediately shorts out the input to schmitt trigger ST, so that the flip-flop FF, cannot be activated. At the same time the signal DS is fed to a pair of delay circuits M1 and M2 arranged to subsequently reset the timers TM1 and TM2, and then to generate a STOP signal returning the circuit arrangement 1 (Fig. 1) to the on-hook state by switching off TR2 via TR and de-energising relay RLA.

Whilst the caller is connected to the switching ciruitry by the relay RLA, a tone is fed to him indicating the state of the appliance. The tone sequence is as follows: Appliance ON - 256 Hz tone Appliance OFF - 2048 Hz tone During the 10 second period preceding the switching of the appliance the above tones are repeatedly switched by a 2Hz warning signal indicating that the switching instant is approaching. The required tones are generated by an integrated circuit oscillator and divider OSC1 and are switched in response to the flipflop outputs and the ten-second pulse by a series of NOR gates G1 to G5. The tone signal is amplified, (and may also be filtered if required) by amplifier A2, and fed to the telephone line via the transformer T,.

It will be understood that the various time periods and tone frequencies chosen above could be varied to suit the user's requirements.

In an alternative embodiment, the unit includes a microphone similar to that of a conventional handset for picking up the sound of a mechanical sound generator, such as a disc rotated by a motor. The motor is set in operation by the incoming call and a vibrating strip engaging serations on the disc emits a sound dependent on the position of the disc.

The motor also rotates a cam for actuating the switching means controlling the appliance, this being arranged so that the state of the switch means corresponds to the presence or absence of a sound from the vibrating strip.

The ringing tone causes the motor to start and the telephone line is connected to the microphone , so that the caller is made aware of the switch state. After 1 5 seconds the motor stops and the line is closed. The cam is arranged so that if the caller rings again the switch means is made to change state. The caller thus has the option of leaving the switch means in its original state, or changing the state by calling again.

Claims

1. Apparatus for remote controlling an electrical circuit via a telephone network, wherein the apparatus comprises an input for connection to a telephone line and a switched output for connection to the electrical circuit, and means coupled to the input responsive to the termination of an incoming call to change the state of the output depending on the duration of the call.

2. Apparatus according to claim 1, wherein the means responsive to an incoming call comprises a detection circuit arranged to sense the presence of a dialling tone on the line, indicative of the termination of the call.

3. Apparatus according to claim 2, includ ing a ring sensor operable to connect a direct current path across the line when a ringing signal is transmitted to the apparatus via the line thereby to put the apparatus in a con nected state which simulates an off-hook con dition, and a timing circuit coupled to an output switching device for operating the out put switching device at the end of a predeter mind time interval commencing with the establishment of the connected state, the said operation of the switching device being condi tional on the apparatus remaining in the con nected state for the duration of the time interval.

4. Apparatus according to claim 3, wherein the dialling tone detection circuit is coupled to means for disconnecting the direct current path to simulate an on-hook condition.

5. Apparatus according to any preceding claim, including a signal generator for transmitting audio signals via the line to a calling apparatus when the apparatus is in the connected state, the signals being indicative of the output state.

6. Apparatus according to claim 5, wherein the signals comprise two tone signals having different frequencies.

7. Apparatus according to any preceding claim, wherein the unit includes a relay con nected to the output for rendering the output alternately open circuit and short circuit.

8. Apparatus according to claim 3, wherein the output switching device includes an input circuit coupled to an output of the timing circuit, and wherein the dialling tone detector circuit is coupled to the said input circuit so as to disable the input circuit in response to sensing a dialling tone.

9. Apparatus according to claim 8, includ ing means for resetting the timing circuit in response to the detector circuit sensing a dialling tone.

10. Apparatus according to claim 9, wherein the resetting means includes a delay element for delaying the resetting of the timing circuit until after the switching device input circuit has been disabled.

11. Apparatus according to claim 10, wherein the dialling tone detector circuit is coupled to means for disconnecting the direct current path to simulate an on-hook condition, the disconnecting means including a delay element for delaying the disconnection until after the switching device input circuit has been disabled.

1 2. Apparatus according to claim 3, in cluding a transformer having a primary winding connectible to the input when the unit is in its connected state, and a secondary winding connected (a) to the dialling tone detector and (b) to the output of a tone generator for indicating to a caller the state of the output switching device.

1 3. Apparatus according to claim 12, wherein the detector circuit includes a filter tuned to a dialling tone frequency.

14. Apparatus for remotely controlling an electrical circuit via the telephone network, the apparatus being constructed and arranged substantially as herein described and shown in the drawings.