AU600523B2 - Apparatus for simulating the dialling pulse switch in a two-loop telephone - Google Patents

Description

6005 23 S F Ref: 33735 FORM COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE: Class Int Class Complete Specification Lodged: Accepted: Published: Priority: Related Art: i~i~i--ELI- Name and Address of Applicant: Address for Service: Siemens Aktiengesellschaft Wittelsbacherp;atz 2 D-8000 Munich 2 FEDERAL REPUBLIC OF GERMANY Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia I. Complete Specification for the invention entitled: Apparatus For Simulating The Dialling Pulse Switch In A Two-Loop Telephone The following statement is a full description of this invention, including the best method of performing it known to me/us 5845/4 _i 1 1 -1

ABSTRACT

APPARATUS FOR SIMULATING THE DIALLING PULSE SWITCH IN A TWO-LOOP TELEPHONE In a holding circuit HI of a two-loop telephone, the current path (Ty, RL, TI) between the wires (al, bl; a2, b2) of the subscriber line, which is provided with a load resistor RL in order to terminate the subscriber line, can be opened and closed with the timing of the dialling pulses by short-circuiting the load resistor for closure. The control of the current path takes place by means of ,O transistors (Ty, Ti, T3, T4) which are controlled by the microprocessor via optical links (Ty, T2, 1 -1IA- APPARATUS FOR SIMULATING THE DIALLING PULSE SWITCH IN A TWO-LOOP TELEPHONE The invention relates to a circuit arrangement for simulating the dialling pulse switch (herein referred to as the NSI-switch) in a two-loop telephone.

Telephone stations of the type known as two-loop telephones ("Two-Loop Telephones", operating instructions published by the West German Post Office FeTAp 2L-716-796), are arranged such that the individual subscriber lines can be selectively connected for example to by means of locking push-buttons and where, for consultation or brokers' calls, holding resistors required between a/b-wires can be o, connected and disconnected hy contacts of the push-buttons or by 'a relay contacts.

In order to avoid the need for relays and structurally elaborate locking push-buttons, it has already been proposed that the requisite holding circuit be constructed electronically so that it can be controlled, by means of a microprocessor contained in the telephone station, via the keyboard (push-button block) of the telephone station. This means that in the hold state a subscriber Q.O line is terminated via a current path containing a holding resistor, and that in the fjllowing operating state (conversation state) of this subscriber line the current path is blocked.

It is an aim ol the present invention to provide apparatus for simulating a dialling pulse switch for use in operation, where the apparatus can be formed as an integrated circuit.

L,

According to the present Invention there is disclosed dial pulse simulating apparatus for a two-loop telephone having first and second sets of subscriber line wires, a microprocessor and a speech circuit adapted to be switched to either set of subscriber line wires, said apparatus comprising: first and second line holding circuits each having a current path arranged between a respective set of said subscriber line wires and that can be switched open and closed by means of a first electronic switching arrangement connected In series with a load resistor of the current path and arranged to be controlled by means of the microprocessor, the load resistor being arranged for conducting current in the line-hold state of the line holding circuit, a second electronic switching arrangement being connected in parallel with the load resistor and being capable of being switched by the microprocessor when said current path is conductive to short-circuit the load resistor to simulate closure of the dialling pulse switch, the opening of said current path by means of said first switching arrangement serving to simulate opening of the dialling-pulse switch.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawing in which the sole figure is a circuit diagrari of a two-loop telephone embodying this invention.

Referring to the drawing, a two-loop telephone has a speech circuit SS comprising a microprocessor M, two holding circuits HI and H2, rectifier bridges Gll and G12 wnich are intended to provide reverse polarity protection, two subscriber lines al/bl and a2/b2 and two line switch-over contacts 11 and 12. The two holding circuits Hl and H2 are of identical construction. The holding circuit Hl is shown

V.'

IAD/986o in detail comprising a thyristor Ty having a holding circuit C/R1, a holding resistor or load resistor RL, a series transistor Tl, transistor opto-couplers T2 and T5, and switching transistors T3 and T4. Also shown are control terminal points for the microprocessor which are referenced ml, m2 and m3 (m4, m5 and m6 for H2).

The operation of the apparatus will now be described: 1) Operation as a holding circuit.

In the rest state of the apparatus, e.g. for the holding circuit HI, no potential is connected to the control points ml, m2 IO and m3. It will now be assumed that dialling and speech is firstly conducted via subscriber line al/bl, and that then, by the actuation of a push-button selected for this purpose, in the .ph-buttn C \o 'UAv O t-e. +&lepVSC"'a block a switch-over is initiated, for example, in order to consult the subscriber line a2/b2, whereby, as a result of the operation of the selected push-buttony it is also indicated that the subscriber line al/bl is to be kept in the hold state. The microprocessor M recognises the subscriber request and switches the switch-over contacts 11 and 12 to the position shown in the drawing. The optically-controlled thyristor Ty receives an ignition pulse via the >0 control terminal ml, as a result of which it switches through and remains switched through by a holding current governed by C and R1.

The current path for the d.c. current connected via the rectifier bridge G11 extends via the thyristor Ty, the load resistor RL and the series transistor T1. The latter is switched conductive since a part of the holding current is diverted from Ty and serves as the base current t the transistor Tl, whereby the holding current for Ty is maintained.

At the same time a continuous potential is connected to the control point m3, so that the transistor opto-coupler T5 is switched through. This switching through means that no base voltage can build up on the base of the transistor T4 via the resistor R2, so that the transistors T3 and T4 are kept in the non-conductive state. As a result the load resistor RL is not short-circuited and can operate as holding resistor.

If the subscriber line al/bl is now reconnected by the SVj VC k SJ k actuation of a push-button/on the pu~sh-but-~el block, to conversation operation (with the waiting subscriber), a pul:se is fed to the transistor opto-coupler T2 via the control point m2. The transistor opto-coupler T2 is switched through and thus diverts the base current from the series transistor TI so that the latter assumes the non-conductive state and thus interrupts the holding current for the thyristor Ty which now in turn also interrupts the current path. As a result, the load resistor RL is disconnected from the subscriber line al/bl. The potential connected to m3 can likewise be disconnected.

The holding circuit H2, which has control points m4, m5 and m6, operates appropriately.

If a holding circuit e.g. H1 is to function as an NSI-switch, it must isolate and short-circuit th wires al/bl of the 4. subscriber line with the timing of the dialling pulses.

In order to short-circuit the wires al/bl, a pulse is fed via the control point ml to the optically-controlled thyristor Ty so that the latter, as already described, switches through, and forms its holding current and the base current for the series transistor L( Tl, whereby the latter likewise switches through. The current path is now switched through. The load resistor RL is now bridged via the diodes Di and D2 and the transistors T3 and T4 (in the form of an arrangement of semiconductor modules), since no potential is connected to the control point m3 and the transistor opto-coupler remains in the non-conductive state and via the resistor R2, from the holding current and from the current flowing through the holding current path, a base voltage can form which switches through the transistors T3 and T4 to short-circuit the resistor RL. The two IO diodes DI and D2 serve to determine the voltage drop which can take place across the resistor R2.

The opening of the NSI-switch, in correspondence with the dialling clock rate, takes place when a control pulse is fed to the control point m2, whereby the transistor opto-coupler T2 switches through, and the base current of the series transistor TI is again diverted so that the series transistor T1 assumes the non-conductive state. As a result the current path is interrupted and the thyristor Ty is switched into the non-conductive state.

The holding circuit H2 functions in a similar fashion for go subscriber dialling via the subscriber line a2/b2. The voltage +UB in the figure is the respective operating voltage of the semiconductor elements Ty, T2 and T3.

It will be clear from the above description that the electronic holding circuit in a two-loop telephone can additionally be used in a simple fashion as an NSI-switch. An NSA-switch (hook switch), which has not been dealt with here, can be formed for example by a switching element of the preferably electronic cradle switch.

-6- The apparatus described above has the advantages that a short-circuit between the a/b wires, which correspond to the closed NSI-switch, and the complete muted isolation of the a/b wires which correspond to the open NSI-switch is provided by means of the holding circuit, that the circuit arrangement can be formed as an integrated circuit, that control of these switching functions is possible using low-power operating elements, and that the subscriber line and speech circuit are electrically isolated.

Claims (8)

1. Dial pulse simulating apparatus for a two-loop telephone having first and second sets of subscriber line wires, a microprocessor and a speech circuit adapted to be switched to either set of subscriber line wires, said apparatus comprising: first and second line holding circuits each having a current path arranged between a respective set of said subscriber line wires and that can be switched open and closed by means of a first electronic switching arrangement connected in series with a load resistor of the current path and arranged to be controlled by means of the microprocessor, the load resistor being arranged for conducting current in the line-hold state of the line holding circuit, a second electronic switching arrangement being connected in parallel with the load resistor and being capable of being switched by the microprocessor when said current path is conductive to short-circuit the load resistor to simulate closure of the dialling pulse switch, the opening of said current path by means of said first switching arrangement serving to simulate opening of the dialling- pulse switch.

2. Apparatus according to claim 1, wherein said first switching arrangement includes a thyristor and a transistor having their main conductive paths connected in series with the load resistor and being independently switchable by means of the microprocessor.

3. Apparatus according to claim 1 or claim 2, wherein said second switching arrangement comprises semiconductor modules which are arranged to provide a normally closed short circuit path across the load resistor.

4. Apparatus according to any one of the preceding claims, wherein the microprocessor is arranged to control said switching arrangements entirely via optical links so that the subscriber line wires are electrically isolated from the microprocessor.

Apparatus according to any one of the preceding claims, wherein each set subscriber line wires is connected to a bridge rectifier circuit for connection to an external subscriber line.

6. Apparatus according to any one of the preceding claims, wherein said line holding circuits are connected to said microprocessor so that D/9o -8- when one of the line holding circuits serves for line holding the other line holding circuit can be contirolled to simulate a dialling-pulse switch.

7. Dial pulse switch simulating apparatus for a two-loop telephone substantially as described herein with reference to the drawing.

8. A two-loop telephone including apparatus according to any one of the preceding claims. DATED this FOURTH day of JUNE 1990 Siemens Aktiengesellschaft Patent Attorneys for the Applicant SPRUSON FERGUSON IA9 /i IAD/986o S\A