NO802825L - Talkback SYSTEM - Google Patents

Description

The invention relates to a telephone system or telephone installation of the type that is sometimes referred to as a star point telephone system. Such a telephone system, which serves for private use for a number of subscriber stations or subscriber devices, for example five such subscriber stations, is arranged to carry out the internal traffic between these subscriber stations via a common intercom line, and external or external traffic can be carried out via a telephone line which is common to the subscriber stations, as each of the subscriber stations is connected to a common processing unit which is designed to control and perform the switching and signaling functions required for handling external and internal traffic.

Such a telephone system is described in the Dutch patent application No. 74 04995 which was laid out on 14 October 1975.

In such a telephone system, the improvement over previously developed systems in this area consists in the fact that each subscriber station telephone set in the system is connected to the central processing unit via a cable containing only four wires. One two-wire circuit forms the voice circuit and the circuit for transmitting ringing signals and selection data over the telephone line, and the other two-wire circuit serves solely for signaling purposes.

In this previously known system, each subscriber station telephone set is provided with a single selection key for internal call signaling. A telephone connection via the intercom line can then be selected by pressing the selection key a number of times corresponding to the identification number of the subscriber station device in the system to be called.

It is an aim of the invention to improve the convenience of operation and use of the previously known telephone system while maintaining the inherent technical advantages.

Another purpose of the invention is to carry out control practically completely by means of electronic devices, with the possibility of using C-MOS technology by using standard components.

For this purpose, a telephone system of the described type according to the invention is characterized by the fact that each of the subscriber station telephone sets included in the telephone system is arranged for each subscriber station telephone set in the system to be selected with a separate selection key which is assigned to the respective subscriber station telephone set , the selection keys being included in a control circuit which, in response to a single operation of a selection key, produces an electrical selection signal that uniquely defines the identity of a called subscriber station telephone set in the system, and that each subscriber station telephone set is further provided with an electric pulse transmitter which is adapted to a) in response to such an electrical selection signal to generate a sequence of selection pulses indicating the identity of the called subscriber station's ion telephone apparatus in the system, and to also b) to provide an initial pulse having a predetermined width and precedes each such sequence of selection pulses, and a device which serves is to open and close a signaling circuit which is connected to the central processing unit under the control of pulses produced by the pulse transmitter.

In order for a subscriber station telephone device for a telephone system according to the invention to be realized using standard components, it is a further feature of the invention that the pulse transmitter comprises a clock pulse source for generating clock pulses each of which has a width that determines the width of the selection pulses, a main counter which can be set using the selection signal and which, in response to a selection signal at its input, performs a number of counting steps corresponding to the value of the supplied selection signal increased by 1, and an auxiliary counter which, in response to clock pulses from the clock pulse source and also to an output signal from the main counter, controls the main counter's counting function in such a way that, by means of a gate control device for combining clock pulses and output signals from the main counter and the auxiliary counter and regardless of the operating period for a respective selection key, at least one is transmitted to the central processing unit complete pulse sequence consisting of a initial pulse and a number of selection pulses indicating the respective called subscriber station telephone apparatus, followed by an incomplete pulse sequence consisting of an initial pulse and one selection pulse.

In order to fulfill the desire that a telephone system according to the invention should be able to be used in combination with unmodified telephone sets of arbitrary construction, according to a further feature of the invention each subscriber station telephone set is composed of a telephone set of normal construction comprising a speech circuit and a separate auxiliary unit comprising said selection keys, a telephone line selection key, a signal lamp, said control circuit and said electric pulse transmitter, and in which current variations in the speech circuit of the telephone set and current variations caused by ongoing on-set and off-set can be detected via an opto-coupler circuit in the auxiliary unit, so that the auxiliary unit , depending on the aforementioned current variations, is or is not operatively connected to the central processing unit via a two-wire signaling circuit.

To further improve the convenience of

use of the telephone system, according to a further feature of the invention it is possible to indicate a call signal that comes in via the telephone line, on all subscriber devices that are connected to the telephone system, by means of an optical signal property of such a call that comes in via the telephone line.

For this purpose, the telephone system, and in particular the central processing unit, according to a further feature of the invention, is provided with an additional signal generator which, in response to a call signal arriving via the telephone line, is connected to a signal generator which is arranged to produce an optical signal indicating that the telephone line is busy, as the signal is then modulated by means of an additional generator with a frequency cr characteristic of the arrival of a call signal via the telephone line.

The invention shall be described in more detail below

in connection with an exemplary embodiment with reference to the drawings, where fig. 1 shows a general block diagram of an embodiment of a telephone system according to the invention, fig. 2

shows a more detailed block diagram of a subscriber station telephone apparatus included in the system shown in fig. 1, fig. 3 shows a first set of waveforms as an illustration of the operation of a pulse transmitter which forms part of a subscriber station ion telephone apparatus, when a selection key is pressed continuously, fig. 4 shows a second set of waveforms as an illustration of the operation of such a pulse transmitter when the same selection key is depressed for a relatively long period of time, fig. 5 shows a third set of waveforms as an illustration of the operation of such a pulse transmitter when another selection key is pressed, fig. 6 shows a more detailed connection core of a connection circuit which is part of the central processing unit and which is arranged separately for each subscriber station telephone apparatus which is part of the system, fig. 7 shows a connection core of a telephone line control circuit which is included in the central processing unit, fig. 8 shows a connection core of a selection register which is part of the central processing unit, fig. 9 shows a set of waveforms illustrating the operation of the selection register shown in fig. 8, and fig. 10 shows a connection core of a base unit which is part of the central processing unit.

In the embodiment of a telephone system according to the invention shown in fig. 1, each of five subscriber station telephone sets TKN1-TKN5 is connected via a cable containing only four wires to the central processing unit which is common to all these subscriber station telephone sets and is shown to the right of the dash-dotted line in FIG. . 1. This processing unit comprises a telephone line control circuit NBK which is common to all subscriber station telephone sets, a selection register KRR which is common to all subscriber station telephone sets, a base unit BED which is common to all subscriber station telephone sets, and a number of telephone set switching circuits TKG1 -TKG5, one for each separate subscriber station telephone set included in the telephone system.

The corresponding connection points or contact terminals in the subscriber station telephone sets and the telephone set connection sockets are in fig. 1 shown by two numbers separated by a period or a dot, the first number serving to indicate the respective contact terminal and the second number after the dot indicating the number of the circuit in which this contact terminal is included. Fig. 1 further shows the way in which the contact terminals on the right side of the respective telephone set connection circuits are connected to the other components of the processing unit.

Each subscriber station telephone set is connected via a two-wire signaling circuit, such as 1.1-2.1, to the corresponding telephone set switching circuit in the central processing unit via the contact terminals, such as c.l-d.l, in the telephone set switching circuit TKG1. Such a signaling circuit is used for the exchange of signals between the respective subscriber station telephone apparatus and the central processing unit, in particular the selection data for the internal call signaling, signals for telephone line traffic with subscriber-owned optical signals, such as telephone line busy signals, telephone line hold signals and telephone line call -waiting signals, as well as signals in connection with callback, transfer and earth function. Each subscriber station telephone set is further connected via a two-wire speech circuit, such as 6.1-4.1, to the associated telephone set switching circuit, such as TKG1, via contact terminals B21.1-B20.1. During normal operation, in reality, the mains voltage protection relay K501 is energized, so that contacts k501 and k'501 are connected to these contact terminals B21.1 and B20.1. Such a voice circuit serves to exchange the voice information between the respective subscriber station telephone apparatus and the central processing unit, at the same time that this circuit also serves to transmit the election data to be transmitted via the telephone lines, as well as the audio signals for internal election purposes, which are received by the respective subscriber station . In fig. 1 further shows that all telephone set connection circuits are connected directly via the respective contact terminals B16 and B18 to the telephone line which ends at the contact terminals Na-Nb.

When the handset in a subscriber station telephone set is lifted off the fork in such a telephone system, this subscriber station telephone set circuit is connected directly to the common line arranged for the termination of internal traffic (the intercom line).

When an internal connection is to be established between a subscriber station telephone device in the system, e.g. the device TKN1, and another subscriber station telephone device in the system, e.g. TKN5, the number of the desired device, in this case 5, can be selected on the calling device by pressing the respective selection key which is arranged for the device number 5 to be called. The selection pulses which are produced in the calling apparatus by pressing the selection key, and which indicate the called subscriber station telephone apparatus, are transmitted via the signaling circuit (1.1-2.1) to the central processing unit, these pulses entering the unit via the contact terminals c1-d.l. Via the associated telephone set connection circuit TKGl, which functions as an intermediate circuit (intermediate connection) between the respective subscriber station telephone set and the other components of this central processing unit which are common to these subscriber station telephone sets, the selection pulses are transferred from the contact terminal Bl.l to the respective input D10 to the election register KRR. The selection register produces an energizing signal on its output D1 which is assigned to subscriber station telephone set no. 5, via the contact terminal B3.5 in the telephone set connection circuit TKG5 which is connected to this called subscriber station telephone set. As a result of this energizing signal, the speech circuit (a.5-b.5) leading to this called subscriber station telephone apparatus No. 5 is switched to a ringing signal circuit (B9.5-B8.5) which is connected to a ringing signal generator (60 volt alternating voltage) which is included in the base unit BED and which serves to generate internal audio frequency ring signals. As a result, the call to the called subscriber station telephone apparatus is announced by means of a buzzer signal which is characteristic of an internal call and which is clearly and audibly different from a ring signal produced in response to a call coming in via the telephone line. The internal connection between the two respective subscriber station telephone devices, in this case devices 1 and 5, is established by lifting the handset of the called subscriber station telephone device from the fork. Such an internal connection is not secret. By lifting the microtelephone, any other subscriber station telephone device can be directly connected to an existing connection without any signal being heard.

Due to the non-confidential nature of such an internal voice connection, an internal conference can take place by calling the respective other subscriber station telephones in the system.

An external or external call coming in via the telephone line from contact terminals Na-Nb is announced in the telephone system by means of one or more bells which may optionally be mounted at a central location or at one or more of the subscriber station telephone sets. In a telephone system according to the invention, such a call that comes in via the telephone line can also be announced by means of an optical signal produced in the subscriber station telephone sets, the optical signal having a flashing frequency that is characteristic of such an external call. Such an external call can be forwarded or answered in each subscriber station telephone set by operating the telephone line key provided in each set. When the telephone line is busy, this is signaled in all subscriber station telephone sets by means of an optical signal, in particular a continuous burning of the respective signaling lamp.

When an external call is answered by a given subscriber station telephone set in the system, all the other subscriber station telephone sets are blocked for external traffic. The same indications and blocks apply to an outgoing connection via the telephone line.

When the telephone system is connected to a telephone exchange which has earthing key functions, the telephone line key in a respective subscriber station telephone set can further function as an earthing key after the telephone line has been assigned.

As soon as a subscriber station telephone set in the system has been connected to the telephone line, this telephone set can be connected to other subscriber station telephone sets in the telephone system by influencing in the respective subscriber station telephone set the selection key associated with the subscriber station telephone set to be called for callback purposes . As a result, the respective subscriber station telephone set is automatically connected to the intercom line while the telephone line is switched to hold. The other subscriber station telephones in the system are alerted to such a situation by means of an intermittent light signal with a flashing frequency characteristic of such a holding condition of a telephone line. At the end of the callback, the telephone line key in the respective subscriber station telephone set can be actuated to reconnect this telephone set to the telephone line in order to resume the call to be conducted over this line. Callback can take place in case of incoming as well as outgoing telephone line traffic.

It is also possible to transfer a connection established between the telephone line and a subscriber station telephone set in the telephone system to another subscriber station telephone set in the system. To this end, the same operations required for callback are performed on the subscriber station telephone set originally connected to the telephone line. When the subscriber station telephone apparatus to which the connection is to be transferred is called, this apparatus takes over the call by operating its telephone line key. The completion of the transfer of the external connection is announced in the transferring subscriber station telephone apparatus by continuous burning of the signaling lamp. The handset in the transmitting subscriber station telephone set can then be put on. Transfer is possible in case of incoming as well as outgoing telephone line traffic.

The telephone system also includes a voltage protection relay K501 which is included in the base unit BED. In the presence of mains voltage for the telephone system, this relay is energized, so that the associated contacts k501, k'501 directly connect the speech circuit in the subscriber station telephone set TKN1 with the central processing unit, contact terminals B21.1-B20.1.

In the event of a failure of the mains voltage, this relay is de-energized and its contacts switched to the rest position, and as a result subscriber station telephone set No. 1 is connected directly to the telephone line. In such a situation, all incoming calls are announced on this telephone set, as traffic via the telephone line is also possible.

The optical busy signaling of the telephone line is realized by means of a signal generator which is included in the base unit BED. The signal generator is arranged to produce a signal with a frequency of 18 kHz and its output is connected to contact terminals B7.1-B7.5 in the respective telephone set connection circuits TKG1-TKG5. The initiating or starting input terminal R501 of this signal generator is connected to the telephone line control circuit's NBK contact terminal C23 via which this signal generator, in the event of occupation of the telephone line, can be initiated from all subscriber station ion telephone devices in the installation, in particular from the contact terminals B4.1 -B4.5 via the telephone line control circuit's NBK respective input terminals C13, Cll, C8, C2 and C5.

This telephone line control circuit further contains a second and a third signal generator. The signals produced by these modulate the signal produced by the first generator in response to the establishment of a hold situation or the arrival of a call via the telephone line. In the event of the establishment of a hold situation, a hold relay K502 is energized and as a result the telephone line is shunted via the relay contact k502 by means of a resistor R550, while at the same time a hold indication is supplied from the respective telephone set switching circuit associated with the subscriber station -telephone device in which the holding situation is produced, from the respective contact terminal B6.1-B6.5 to the telephone line control circuit's respective contact terminal C15, C12, C9, C6 or C3. As a result of this, in addition to an energizing signal for the holding relay K502, a start signal is produced for the second signal generator which then modulates the signal for the first generator with a signal characteristic of the holding situation. In the case of a call coming in via the telephone line (terminals C21-C26 in the telephone line control circuit), the third signal generator can similarly be operatively coupled to the first signal generator so that the latter is modulated with a signal characteristic of the call received comes in via the phone line. The earthing relay K301 which is part of the telephone line control circuit NBK, can be energized from each of the subscriber station telephone sets via the associated telephone set connection circuit, namely from the respective contact terminal B2/5.1-B2/5.5 and via the telephone line control circuit's respective contact terminal C14, CIO, C7, Cl, C4.

The selection register KRR has five separate inputs, more specifically the contact terminals D10, D8, D6, D4 and D2, which are connected to an associated one of the telephone set connection circuits, in particular the contact terminals Bl.1, Bl.2, Bl.3, Bl.4 and Bl. 5. The respective outputs from this selection register KRR, more specifically contact terminals D9, D7, D5, D3 and D1, are connected to the respective inputs of the relevant telephone set connection circuits, in particular terminals B3.1, B3.2, B3.3, B3. 4 and B3.5.

After the previous, general description of the telephone system, the individual elements of this system will now be described in more detail.

Fig. 2 shows a detailed connection core of one

of the subscriber station telephone sets TKN1-TKN5. Such a subscriber station telephone set comprises two separate circuits, i.e. a circuit for the transmission of speech and acoustic ringing signals (internal) and which terminates in contact terminals 6.1-4.1, and a circuit for the transmission of control signals and signaling signals, and which terminates in contact terminals 1.1 and 2.1. The speech transmission circuit is of conventional construction and comprises an acoustic ringing signal generator H101 which is connected via a fork contact K109 to be affected by the microphone over the two-wire circuit which is connected to the central processing unit. If the subscriber station telephone set includes a selector dial, the conventional spark arrester circuit comprising capacitor C107 and resistor RI08 is hardwired across pulse contact K108 to be affected by the selector dial,

so that the conventional, second fork contact K107 to be affected by the microphone is available for a function in the second circuit that serves for control sig-

the nals and the signaling signals and which end at the contact terminals 1.1 and 2.1. If, instead of a selector dial, the subscriber station telephone set includes push-button keys for tone frequency selection signals, this spark arrester circuit is absent. Such a selector dial or such tone-push-button keys are used for transmission of selection data via the telephone line. .For the purpose of establishing an internal connection, the subscriber station telephone set further comprises a number of selection keys, which number is equal to the number of subscriber station telephone sets that can be connected to the telephone system. In the present embodiment, the maximum number is equal to five. These selector keys K102, K103, K104, K105 and K106 are part of a control circuit which has three output conductors which end at setting inputs 4, 12 and 13 to an adjustable up/down counter D101 which will be described later. The subscriber station telephone apparatus further comprises a telephone line key K101 and an optical signaling device in the form of a light emitting diode (LED) B101.

Various signaling signals can be transmitted from the subscriber station telephone apparatus via the signaling circuit from the contact terminals 1.1-2.1 to the central processing unit. The setting and zeroing signals, which correspond to a lift-off state and a put-on state respectively of the handset, take effect as a voltage drop over respectively an interruption of the signaling wires that end at these contact terminals 1.1 and 2.1.

When the telephone line key K101 or the grounding key is pressed, these signaling circuit wires are short-circuited, and as a result, the voltage drop across the device's power supply (via V102 and V105) is cancelled. In other words, the signaling wires 1.1 and 2.1 are short-circuited, resulting in a voltage rise at the side of the central processing unit, which voltage rise indicates the actuation of the telephone line key.

By pressing one of the selection keys K102-K106

the pulse transmitter which is part of the subscriber station telephone apparatus and which comprises the aforementioned, adjustable up/down counter D101, is affected via the aforementioned control circuit, so that

the signaling circuit which is connected to the central processing unit, as long as the respective selection key is affected,

in the form of line interruptions transmits cyclically occurring pulse sequences indicating the called subscriber station telephone apparatus in the telephone system, to the central processing unit in which unit these pulses are interpreted and

■ is counted.

The various signals which serve for optical signaling of the respective subscriber station telephone apparatus, in particular the telephone line busy signals, the telephone line hold signals and the external telephone line call signals, are transmitted respectively in the form of a sine voltage of 18 kHz, a sine voltage of 18 kHz modulated with 1 Hz and a sine voltage of 18 kHz modulated with 4 Hz, from the central processing unit via the two signaling wires and via contact terminals 1.1 and 2.1 to the subscriber station telephone set. In the telephone set, these 'signals, via a capacitor C105, an inductor T103 and a capacitor C11 forming a resonant circuit, can be reproduced by the optical signaling device B101 which is a light emitting diode.

The selection keys K102-K106 are further arranged so that the optical signaling device B101 is short-circuited in response to the influence of one of these selection keys, and as a result, selection pulses are prevented from being reproduced by this signaling device B101 when such pulses are transmitted via the signaling circuit 1.1-2.1.

The electronic section or part of the subscriber station telephone apparatus receives electrical power via a zener diode V105, a diode V104 and a buffer capacitor C104. A transistor V102 is controlled by the pulses produced by the pulse transmitter, and interrupts the signaling circuit which ends at the contact terminals 1.1 and 2.1, in time with the pulses supplied to this transistor. By means of a choke coil T101 which is connected in series with this transistor, drive signals for the optical signaling device B10.1 are prevented from affecting the operation of the pulse transmitter and its supply.

Each subscriber station telephone set in the telephone system includes an individual pulse transmitter which is composed of integrated circuits D101, D102 and D103. The integrated circuit D101 is an adjustable, binary working up/down counter of known design. Such a counter can count either in binary fashion or in decades depending on the voltage level applied to its input terminal 9. If a logical "one" is applied to this terminal, the counter counts in binary fashion. In a similar way, it can be achieved that the counter counts upwards in response to the supply of a logical "one" to the terminal 10 and vice versa. When a logical "one" is applied to the input terminal 1, the counter is free to be set via the inputs terminating at the contact terminals 4, 12, 13 and 3, to a given value and without synchronism with clock signals applied to a terminal 15. Such counter is further arranged so that it is advanced one step in response to a positive edge of the clock signal which is supplied to terminal 15, if a logical "zero" has been supplied to the inputs ending at terminals 5 and 1. The course of the counting operation is prevented if a logical "one"

.is supplied either to one or the other or to both of these clamps. Terminal 2 constitutes an output via which

one output pulse is generated for each pair of counted clock pulses.

Each of the integrated circuits Dl02a and Dl02b is

a binary up-counter of known arrangement. Each of the two identical counters D102a and D102b is a four-step counter. These counting stages are arranged as switchable flip-flops which are arranged to switch one counting stage forward in response either to a positively directed edge of a clock pulse supplied to a clock pulse input 1, 9 of the respective counter, or to a negatively directed edge of a trigger pulse which is supplied to the appropriate input 2, 10 of the respective counter. Each counter can be reset asynchronously by means of a high-level signal on the respective reset input 7, 15. Such a counter is consequently advanced one count step in response to the simultaneous presence of a positive edge of a clock signal pulse,

a "one" of the trigger signal and a "zero" of the reset signal, or the simultaneous presence of a "zero" of

the clock signal, a negative-going edge of the trigger signal and a "zero" of the reset signal. Terminals 3 and 4 are the Ql and Q2 outputs of one counter, and terminal 12

is the Q2 output of the second counter.

The pulse transmitter also comprises a clock pulse generator with two NOR gates Dl03a and Dl03b.

The control circuit in which the selection keys K102-K106 are connected is arranged so that in response to the influence of one of these selection keys, a voltage pattern is produced on the three output conductors of this control circuit which are connected to the counter's D101 terminals 4, 12 and 13. This voltage pattern is .characteristic of the identity of the subscriber station ion telephone apparatus to be called, as indicated by the actuation of the respective selection key. Actuation of the selection key K106 results, for example, in obtaining a voltage pattern +-+ on the three output conductors, which voltage pattern is representative of the number five, in other words the subscriber station telephone set which has the number five. The counter D101 can be set with the help of this control circuit so that the counter, in response to the supply of a release signal to terminal 1, is set to the value indicated by this control circuit independently of the clock pulses. which is supplied to the input terminal 15.

The mentioned counters, the clock pulse generator which is connected to the counter's D102a trigger input 2, and the two NOR gates D103c and D103d are interconnected so that each cycle of pulses produced by the pulse transmitter each time begins with a fixed pulse of 40 ms. This pulse is recognized in the central processing unit as a reset pulse for the counters included in the election register. After such an initial pulse, a number of selection pulses, each • having a width of 2.5 ms and as determined by the clock pulses, are emitted. The number of transmitted selection pulses of one cycle is equal to the number of the selected subscriber station telephone set plus one. When a respective selection key is released, either the current pulse cycle is completed or one initial pulse with one selection pulse is emitted, depending on the moment at which the respective selection key is released.

However, this latter pulse combination will not be recognized in the central processing unit. The connection between the counter's D102a Q2 output (terminal 4) and the counter's D101 input (terminal 3) prevents the "latch-up" effect when switching on the supply voltage.

The operation of the pulse transmitter described above is shown in detail in fig. 3, 4 and 5. Fig. 3 illustrates the situation in which the key K106 (for selecting telephone device no. five) is affected for a relatively short period of time (line 31). Line 32 represents the signal that is developed on the counter's Dl02b Ql output (terminal 11) in response to the action of this key. Line 33 represents the clock pulses that are developed by the clock pulse generator on the NOR gate D103a terminal 3 in response to the influence of the relevant selection key. Line 34 represents the signal developed on the counter's D101 Q4 output (terminal 2), while line 35 represents the trigger pulses developed by the counter D102a on terminal 3, which trigger pulses are fed to the counter's D101 trigger input (terminal 1). As a result of this, a signal represented by line 36 is generated on this counter Dl02a terminal 4, which results in a signal represented by line 37 being generated on the NOR gate Dl03d output, which signal is fed to the NOR gate Dl03c one input 9. The control signal for the transistor V101 as ultimately produced by the pulse transmitter is represented by line 38, from which it appears that, as a result of the action of the selection key for subscriber station telephone set No. 5, a pulse cycle consisting of an initial pulse of 40 ms is produced followed by a number of six selection pulses, while it also appears that after releasing the respective selection key, only one selection pulse is still emitted.

After releasing a selection key, the pulse transmitter will generally complete a pulse cycle that was initiated by the actuation of the key. Regardless of the moment at which the respective selection key is released, at least one complete pulse cycle (a set of selection pulses indicating the called telephone set, and a reset pulse) and a selection pulse with a reset pulse will be produced. However, a combination of the last mentioned two pulses is not recognized by the electoral register. After a selection key has been released, the internal ring signaling stops. In other words, the ringing signal generated on the called telephone set stops, and is therefore represented as a (non-intermittent) signal only as long as the respective selection key is pressed. Fig. 4 illustrates the situation in which the selection key in subscriber station telephone apparatus No. 5 is affected for a relatively long period of time (line 41), in which case two successive sequences of six selection pulses each are produced (line 48). The lines 41, 42, 43, 44, 45 and 48 which are shown in fig. 4, corresponds to each of the lines 31, 32, 33, 34, 35 and 38 in fig. 3. Fig. 5 shows the situation in which the selection key K102 for subscriber station telephone set no. 1 is affected. The lines 51, 52, 54, 55 and 58 shown in fig. 5, corresponds to each of the lines 31, 32, 34, 35 and 38 in fig. 3.

When the microphone of the respective subscriber station's ion telephone device is lifted, the fork contact K107 is closed, in which case the pulses produced by the pulse transmitter are transmitted to the central processing unit in the form of interruptions of the signaling circuit extending via the contact terminals 1.1 and 2.1.

In order to fulfill the desire that a telephone system of the present type should be able to be used in combination with unmodified telephone sets of arbitrary construction, an auxiliary unit has been developed which can be used as a console for such a telephone set, which auxiliary unit accommodates the part of that in fig. . 2 showed subscriber station telephone apparatus connected to the signaling circuit (1.1-2.1). A telephone device to be used in combination with a

such auxiliary unit can be connected to the auxiliary unit without any further adaptation being necessary. In connection with this and as a result of the fact that the fork contact function of the mechanical contact K107 (Fig. 2) must be realized by electronic means, the speech circuit of the respective subscriber station telephone set is electrically connected via a cable leading to the auxiliary unit of a light-emitting

diode included in the speech circuit, which light-emitting diode is connected in series with a current-limiting resistor to form one diagonal branch of a four-arm, rectifying bridge circuit of which the other diagonal branch is connected across the speech circuit of the subscriber station telephone set. This rectifying bridge circuit is arranged to make the signaling circuit to be connected insensitive to polarity changes in the speech circuit. A zener diode is connected in parallel with the series circuit formed by the light-emitting diode and the current-limiting resistor, to achieve that the line current flowing through the speech circuit can vary between approx. 5 and 150 mA without a current higher than the permissible maximum value flowing through the light-emitting diode. This light-emitting diode is optically coupled to a phototransistor adapted to switch on a line current as low as 4 mA. The current that flows through the light-emitting diode will then be approx. 3 mA. When the line current in the speech circuit is 100 mA, the current that in this device flows through the light-emitting diode has only increased to approx. 15 mA, and as a result this circuit arrangement is universally applicable. The fork contact function of the mechanical contact K107 (fig. 2) is taken over in the auxiliary unit by a switching transistor which is connected to the phototransistor. As a result of the optical coupling between the light-emitting diode and the associated phototransistor, the coupling transistor, when the handset of the subscriber station telephone set is lifted or put on, will connect or disconnect the wire in the signaling circuit that ends at the contact terminal 2.1 (Fig. 2) to, respectively, from the connection point between the choke coil T101 (fig. 2) and the connection with the telephone line key K101 (fig. 2). The selection pulse circuit for internal signaling and the optical telephone line signaling described in connection with fig. 2, can be used in unmodified form in this auxiliary unit. The open circuit of this coupling transistor, which is connected to the phototransistor, is further attenuated by a capacitor which is connected to the base-emitter circuit of the coupling transistor, so that the interruptions in the speech circuit caused by the influence of a selector dial when a telephone set is used together with a selector dial , does not affect the correct operation of this opto-electric switching circuit. By means of a capacitor which is connected between the emitter and collector of the switching transistor, this transistor is further short-circuited to the alternating voltage which is responsible for the optical telephone line station.

Fig. 6 shows a more detailed diagram of one of the telephone set connection circuits TKG1-TKG5 according to fig. 1.

A separate such telephone set connection circuit is arranged for each subscriber station telephone set connected to the telephone system, each telephone set connection circuit in reality forming an intermediate circuit (intermediate connection) between, on the one hand, the relevant subscriber station telephone set and, on the other hand, the other components in the central treatment unit. If less than the maximum number of subscriber station telephone sets are connected to the telephone system, the telephone set connection circuits, which are in the form of modules, for these unconnected subscriber station telephone sets can also be bypassed without affecting the correct operation of the remaining components and without any adaptation of the system being necessary.

A telephone set switching circuit is operatively involved in the following system functions: the telephone line function, the transmission of selection pulses for internal signaling, the control of the hold relay in connection with the telephone line hold condition, the recognition of a circuit break caused by a handset jack, the control of the ground relay in connection with ground line functions, the control of an energizing circuit for the internal ringing signals and the transmission of signals for the optical signaling in a subscriber station telephone apparatus.

The one in fig. 6 showed telephone set circuit

is assumed to be connected to the subscriber station telephone set TKN1, the contact terminals of this telephone set connection circuit being provided with the same reference numbers as the telephone set connection circuit TKG1 which is shown in the block diagram of fig. 1.

The one in fig. 6 shown telephone set connection circuit comprises a contact terminal B19.1 via which signaling signals transmitted from the associated subscriber station telephone set as a result of the action of the fork contact, one of the selection keys or of the telephone line earthing key can be received and signals for the optical signaling in the respective subscriber station telephone set can be transferred to this. Two voltage-sensitive input circuits comprise transistors V202 and V201 is connected via a choke coil T201 to this terminal B19.1. When the fork contact K107 in the associated subscriber station telephone set is open, in other words when the handset is on, the voltage for the input circuit of the transistor V202 which occurs at the connection point between two resistors R208 and R209 is equal to zero, while at this connection point, when this fork contact K107 is closed and this signaling circuit does not open as a result of an interruption as a result of a selection pulse for the internal ringing, a voltage in the range from 6 to 10 volts is present,

depending on the resistance of the connected signaling circuit. Since a threshold circuit is included in the input circuit of the transistor V201 (a zener diode V205 forms an input threshold of 13 volts), this transistor V201 does not respond to such voltages in the range of 6 to 10 volts. When the transistor V202 is made conductive as a result of such a voltage in the range of 6-10 volts at the connection point between the resistors R208 and R209, two controllable flip-flops D203a and D203b become

which are arranged as identical JK flip-flops, triggered via two flip-flops D204a and D204b and an AND gate D202b. At the same time, an AND gate D202c is blocked via a flip-flop D204c.

When the telephone line key K121 is actuated in the associated subscriber station telephone apparatus, as a result of this the signaling circuit terminating at the contact terminals 1.1-2.1 (Fig. 2) is short-circuited, resulting in an increased voltage in the range of 15 - 18 volts, depending on the resistance of the signaling circuit connected to this occurs at terminal B19.1 of the telephone set connection circuit. As a result, the zener diode V205 is made conductive when the applied voltage exceeds the threshold voltage of 13 volts, so that the controllable flip-flop D203a switches via the transistor V201, delay and disturbance cancellation circuits comprising a capacitor C203, a resistor R203 and a flip- flop D204d, and an AND gate D202a, resulting in energization of telephone line relay K201. As a result of this, relay contacts k201-k'201 will be switched, so that the speech circuit that ends at contact terminals B21.1 and B20.1 is connected via terminals B16.1 and B18.1 to the telephone line (Na-Nb, fig. 1). As a result of the influence a<y>this telephone line relay K201

in other words, the associated subscriber station telephone device is connected to the telephone line. As a result of the switching of the flip-flop D203a, this flip-flop is at the same time blocked, so that the flip-flop remains in the switched state. Such blocking is likewise realized when another subscriber station telephone set connects itself to the telephone line by acting on the telephone line key in this telephone set, in which case the respective blocking signal enters this telephone set connection circuit via terminal B17.1. As a result of such blocking, such a connection established via the telephone line will remain secret.

The blocking signal produced by the switching of flip-flop D203a leaves the telephone set switching circuit via line B4.1, resulting in the initiation of the signal generator for the optical telephone line indication, as will be described later.

For completeness, it should be noted that the flip-flop D203b is also switched during the selection of the telephone line.

The pulses sent by the pulse transmitter in the associated subscriber station telephone apparatus and which were discussed in connection with fig. 2, comprises a number of selection pulses, which number is equal to the number of the called subscriber station telephone set multiplied by one, each of the selection pulses having a width of 2.5 ms. Each such group of selection pulses is followed by a pulse with a width of approx. 40 ms which is operative as a reset pulse for the selection register. The total duration of such a group of selection pulses and an associated reset pulse is a maximum of approx. 60 ms, so that the internal selection is carried out with a repetition rate of

at least approx. 17 times per second. Such selection pulses act as interruptions of the wires in the signaling circuit and are formed into square pulses via the transistor V202 and the flip-flop D204a, and the pulses are later supplied via the flip-flop D204b and the AND gate D201a via the line Bl.1 to the selection register KRR which will be discussed below.

When a subscriber station telephone set is connected to the telephone line, as already stated above, both flip-flops D203a and D203b are switched and maintained in the switched state. When these two flip-flops are switched, no change occurs at the output of the AND gate D201c which is connected via line B6.1 to the hold relay K502 (Fig. 7) which serves for telephone line hold switching, so that the hold relay K502 is not energized when a respective subscriber station telephone device is connected to a telephone line. When, however, e.g. by pressing the selection key, the respective subscriber station telephone set is again disconnected from the telephone line and again connected to the internal line common to all subscriber station telephone sets, the flip-flop D203a will be switched back again by means of the selection pulses as on

new arrives at terminal B19.1 via flip-flop D204b. However, the flip-flop D203b is now not switched back as the delay circuit with resistors R211, R212 and a capacitor C206 blocks the pulses that are now transmitted from the subscriber station telephone apparatus, so that no flip-flop reset signal is generated via the AND gate D202b -flop D203b. As the flip-flop D203a is now switched back and the flip-flop D203b is not switched back, a status change will be produced at the output of the AND gate D201c by means of which the holding relay K502 is energized and the telephone line is switched to the holding position via the relay contact k502. Likewise, the aforementioned second signal generator is operatively connected to the first signal generator, so that an optical signaling characteristic of the holding situation can also be provided.

The hold relay will again be triggered when the telephone line later, from the respective subscriber station telephone set,

is again selected, whereby the flip-flop D203a is again switched.

When the microphone is applied and as a result the fork contact K107 is open/the flip-flop D203b will also be switched back, so that the original idle state has returned.

The resistance connected through the speech circuit during the energization of the holding relay K502 has a magnitude of 560 ft.

As already explained above, the controllable flip-flop D203a is switched back as a result of selection pulses arriving via the terminal or line B19.1 for the internal ring signals. The flip-flop D203a will also be switched back when the respective subscriber station telephone set jack K107 is opened as a result of hanging up the handset. However, the controllable flip-flop D203b is switched back only as a result of an interruption of the signaling circuit produced by the respective subscriber station telephone fork contact. The delay circuit R211, R212 and C206 are in fact dimensioned for a delay of 100 ms, which delay time is not achieved with the pulses transmitted by the respective subscriber station telephone apparatus pulse transmitter. A reset pulse of 40 ms produced by the aforementioned pulse transmitter is therefore exclusively operative for zeroing the yet-to-be-mentioned counter which is linked to the selection register.

"Flip-flop D203b can also be switched back from

an AND gate D201d through which the output signals from the flip-flops, such as D203a, which are, however, included in the telephone set switching circuits associated with each of the other subscriber station telephone sets, are compared with the output signal from the flip-flop D203a in the telephone set switching circuit for the respective subscriber station telephone apparatus, to prevent the telephone line from being switched into the hold position if another subscriber station telephone apparatus were to break the connection with the telephone line.

Under given conditions, it is desirable to connect one or both wires in the telephone line to earth, and for this purpose the telephone set system is provided with an earthing relay K301 (fig. 7). From each of the subscriber station telephone sets, this earthing relay can be actuated via the associated telephone set switching circuit, namely by again actuating the telephone line key after the said telephone line key, such as K101, has been actuated for the first time from the respective subscriber station ion- telephone set. When the telephone line key is actuated for the first time, as already explained above, the controllable flip-flop D203a is blocked while at the same time the AND gate D20 2a is also blocked. AND gate D201b now combines a signal level change produced by a second and possible subsequent operations of the telephone line key with the signal produced at the output of flip-flop D204f,

so that when the telephone line key is depressed for the second time, a status change is produced at the output of the mentioned port D201b which via the line B2/5.1 and via the not yet mentioned telephone line control circuit NBK energizes the earthing relay K301. In this way, the relay contacts k301 and/or k'301 are switched, so that the desired earth connection is formed.

Each telephone set connection circuit further comprises a ring signal relay K202 for the internal, acoustic ring signal. The binary control signal for the ring signal relay is produced by the selection register KRR, and this signal is supplied via line B3.1 to the transistor V203 and a control circuit comprising an AND gate B202c for the aforementioned ring signal relay K202. When the relay is energized, the relay contacts k202 and k'202 are switched, so that the speech circuit for the respective subscriber station telephone device is connected to an alternating voltage of approx. 60 V and a frequency of 50 Hz produced by a generator connected to the base unit BED for producing the acoustic ringing signal for the internal ringing signalling. When the microphone for the respective, thus called subscriber station telephone device is lifted, the port D202c becomes blocking, so that the mentioned ringing signal relay K202 is triggered.

As already mentioned above, the generator for the optical signaling produces a sinusoidal voltage with a peak-to-peak value of 20 V and a frequency of 18 kHz, such a signal being operative for the optical signaling being transmitted via conductors B7.1 in the respective telephone set connection circuit. In said conductor is connected a tuned circuit comprising a resistor R219, an induction coil T202 and a capacitor C209 to hold high frequency radiation produced by it. said signal of 18 kHz within the given norms. The capacitor C201 forms an alternating voltage separating capacitor by means of which the alternating voltages produced in the respective subscriber station telephone apparatus's signaling circuit are separated from the aforementioned signal generator's output amplifier. By means of the choke coil T201, the signal with the frequency of 18 kHz is produced with such a high impedance that the sine signal does not exert any influence on the digital control. Resistor R219 also has a current limiting function.

To exclude damage and/or errors in a speech circuit, two protection resistors R215 and R218 are connected. Likewise, protective resistors R216 and R217 are arranged for the internal ringing.

Fig. 7 shows a more detailed diagram of a telephone line control circuit NBK which is common to all subscriber station telephone sets and telephone set connection circuits. The control circuit NBK forms part of the central processing unit and is operatively linked to the implementation of the following functions: Provision of the blocking in connection with the telephone line function, control of the holder relay, control of the earthing relay, processing of a call coming in via the telephone line or the external connection, start of the optical telephone line busy signal, generating an optical signal characteristic of the call coming in via the telephone line, and generating an optical signal characteristic of the hold state.

When a subscriber station telephone set is connected to the telephone line, a characteristic indication for this is emitted at one of the respective inputs C5, C2, C8, Cll, C13, and this from the telephone set switching circuit associated with the subscriber station telephone set that has been connected to the telephone line. As a result of such a telephone line indication, at the output of an AND gate D305a, a change of status will occur which will be transmitted without delay via wires C20 and C24 to all telephone set connection circuits (contact terminals B15.1 - B15.4 and B17 .1 - B17.5). As a result, the call connection established through the telephone line remains confidential. Via a circuit comprising a diode V315, two resistors R320 and R321, a capacitor C309 and a flip-flop D307e, a connection is introduced so that the blocking signal on wire C19 will only be triggered 1.5 seconds after the termination of the telephone line's busy condition. Such a release signal is supplied to all telephone set connection circuits, to the respective contact terminals B14.1 - B14.5. Within this time interval, the public switchboard to which the telephone line is connected will be disconnected, so that a call as soon as it has been terminated cannot be taken from a different subscriber station telephone set.

The hold relay K502 which is provided for the hold state of the telephone line is energized from the telephone line control circuit via its output wire C22. Contact terminals B6.1 - B6.5 in the respective telephone set connection circuits TKG1 - TKG5 are connected to inputs C15, C12, C9, C6 and C3 in an input circuit comprising AND gate circuits D306a and D301a in the energizing circuit for this holding relay K502. The output signals from these input port circuits control a switching transistor V302, the arrangement being such that, when the telephone line is switched to the hold state from one of the subscriber station telephone sets, - a change of state occurs at the respective of the aforementioned inputs C15 - C3, and as a result of this switches the transistor V302 to the conducting state and the holding relay K502 is energized. This relay K502 is included in the basic unit BED.

The telephone line control circuit also provides for energizing the grounding relay K301, specifically via an input circuit comprising AND gate circuits D305b and D303a in this energizing circuit. Contact terminals B2/5.1 - B2/5.5

in the respective telephone set connection circuits TKG1 - TKG5 are connected to the inputs C14, CIO, C7, Cl and C4 in this input circuit, so that a change of status occurs on the

respective of these inputs when a ground key function is initiated from one of the subscriber station telephone sets, and as a result the switching transistor V303 in this energizing circuit is switched to the conducting state so that the ground relay is energized and the desired ground connection is made. If desired, only the a wire in the telephone line can be connected to ground by looping a wire bridge.

If no grounding button function is required, the grounding relay K301 can be switched out of operation by removing the respective wire bridge from its plus wire. This prevents unwanted connection clicks and unnecessary energy consumption.

In this connection, it should be noted that the input circuits described above can be built with standard building blocks in C-MOS technology, and this due to the fact that every fifth input to these input circuits is fed to one input of a separate AND gate circuit.

From the input circuit consisting of gates D305a and D301c, it is also achieved, via one of the circuit's inputs C13-C5, that the switching transistor V301, via a flip-flop circuit D307e and two AND gates D306b and D303b, is switched to the conducting state, and which as a result, a start signal is produced via wire C23 for the signal generator included in the base unit BED for providing the optical telephone line busy signal. As stated above, such a busy indication is provided by a signal lamp which lights up continuously in the relevant subscriber station telephone set.

The telephone line control circuit is also provided with a signal generator with an associated input circuit as a result of which it is possible, in the event of a call arriving via the telephone line, for the signal generator in response to the ringing signal thereby received to be operatively coupled to the above-mentioned signal generator which provides the optical telephone line - busy signal, so that a resulting signal is produced which is characteristic of the incoming call via the telephone line. As a result, this situation can be indicated in the respective subscriber station telephone sets by means of an optical signal with a characteristic flashing frequency (4 Hz). The input circuit is connected to the telephone line via wires C21 and C26. During an existing call or conversation connection, this circuit remains connected to the telephone line as this circuit represents a high-ohmic input impedance. This circuit comprises a four-arm diode bridge circuit with diodes V306, V307, V308 and V309. This bridge circuit rectifies a ringing signal (frequency 25 or 50 Hz) that comes in via the telephone line, and the rectified signal is operative for connecting an opto-coupler D302

(of similar construction to the one used in the auxiliary unit mentioned above), which is the result of which a triac V311 is connected via resistors R312 and R310, a transisotr V304 and a resistor R311. As a result of this becomes

the connected telephone line bells (not more than five) supplied with ring current from the supply transformer included in the base unit BED, for providing acoustic signals that a call is coming in via the telephone line.

During an existing telephone line connection, the opto-coupler D302 is disconnected via the blocking lines and the flip-flop D307d, so that selection pulses do not affect the signaling functions.

As a result of the switching of the transistor V304 in response to a call coming in via the telephone line, it is also achieved that the previously mentioned signal generator for optical signaling of the situation that a call has come in via the telephone line is operatively connected to the signal generator h for the optical telephone line busy signal . For this purpose, the output of this transistor V304 is also connected to a delay circuit comprising a resistor R309 and a capacitor C305, whereby the intervals of the ringing signal arriving via the telephone line are filled in, so that when such a telephone line call occurs there is a constant signal at the output of the flip-flop circuit D307f. This signal causes the signal generator comprising AND gates D304c and D304d to produce a square wave signal with a frequency of 4Hz. This signal generator is started via gate D304b, the output signal being supplied via AND gate D306b (input contact 11) and via gate D303b and transistor V301 as a modulation signal to the signal generator to produce a sine wave with a frequency of 18 kHz. Resistors R304 and R305 limit the voltage on the gate inputs of this modulation signal generator.

For optical telephone line hold signaling, the telephone line control circuit further comprises a further modulation signal generator which is dimensioned so that it is capable of producing a square wave output signal with a frequency of 1 Hz, so that an optical signal characteristic for the hold condition can be produced by means of this. In response to an energizing signal generated for the above-mentioned holding relay K502, this further modulation signal generator is started from the gate D301a, so that this square-shaped modulation signal via the AND gate D303b and the switching transistor V301 is combined with the signal from the above-mentioned signal generator to generate a sine wave with frequency 18 kHz.

The telephone line control circuit also makes it possible to use the telephone system in combination with a different (household) automatic device, such as a WB device. The

is it then possible that the telephone system's optical simulation can be switched from the other system. This possibility is provided via an input circuit which comprises a switching transistor V317. For this purpose, lead wires C30 and C31 are connected to contact terminals BSa and BSb to which the second system is connected. When these contacts as a result of a coupling function in the second system are connected together (to a maximum impedance of 10 kfi), the transistor V317 starts the aforementioned signal generator to produce a sine wave with a frequency of 18 kHz via the gates D304a , D306b and D303b and the transistor V301. Telephone line call signaling

and telephone line hold signaling has priority over this busy signaling (D304a and D303b).

Fig. 8 shows a more detailed diagram of the aforementioned selection register KRR which serves for internal ringing. Like the telephone line control circuit and each of the telephone set connection circuits used, this selection register is a module unit which forms part of the central processing unit.

The selection register comprises five identical input circuits with blocking possibilities, a counter, a read/zero position circuit and an output circuit. Each of the input circuits is connected to an associated one of the telephone set connection circuits. In a system with five subscriber station telephone sets, terminals Bl.1 - Bl.5 in the respective telephone set connection circuits are therefore connected to the selection register inputs D10, D9, D6, D4 and D2.

Each of these input circuits comprises a controllable, bistable circuit (J-K flip-flop), such as D401b, D401a, D402b, D402a and D403a. Using a delay circuit consisting of a diode, two resistors and a capacitor, e.g. diode V401, resistors R401 and R402 and capacitor C401 in the case of flip-flop D401d, the respective input circuit is rendered insensitive to spurious pulses, and the respective flip-flop is not triggered via input R until approx. 20 ms after an incoming switching edge.

Since a pulse sequence emitted by the respective pulse transmitter for internal ringing, as stated above, always begins with an initial pulse that acts as a reset pulse (approx. 40 ms), the respective flip-flop, e.g. D401b, always be in such a state that it lets through the first selection pulses of the pulse sequence via the associated AND gate D404c. The flip-flop 401b is further arranged so that upon receipt of such a pulse sequence, it blocks the selection register's other input circuits, so that the selection register cannot receive more than one pulse sequence at a time. Such blocking is achieved as a result of the fact that the respective outputs from these flip-flops, which form part of the input circuits, are connected to 0G gates D405a and D409b, the input flip-flops being blocked via the flip-flop circuit D409c and via their respective J and K inputs. A sequence of pulses transmitted by the respective input flip-flop, such as D401b, can reach the counter's D408 count input via gates D405b and D409a. A pulse sequence supplied to this counter input consists of two selection pulses and one reset pulse when the subscriber station telephone set is to be called. The two selection pulses give three edges from zero to one, so that when subscriber station telephone set No. 1 has been selected, this output is activated from the counter D408 which corresponds to this telephone set (wire 7).

Each of the counter's outputs corresponds to one of the subscriber station telephone sets in the telephone system and is connected to an associated, separate input to an output circuit designated as a 6D flip-flop which is operative as a memory circuit. Counter D408 reset input R and read input Cl and reset input R of said output circuit D407 are connected to a read/reset circuit comprising gates D406a, D406b and D409b. A diode V406, a resistor R411, a capacitor C406 and a resistor R412 constitute a delay circuit by means of which the selection pulses (2.5 ms) coming from the gate D4 09a are suppressed, so that on the input 2 of the gate D406a exclusively reset pulses be present. As a result of such a reset pulse, a one-level with a duration of approx. 35 ms. However, when selection pulses are supplied from the gate D409a, the gate D406b's input 5 is at zero level, so that the said selection pulses have no influence on the output signal of the gate D406b. The aforementioned one-level which is produced on the gate D4 06b input 5 is used for reading the memory D407. In response to the positive edge of the read pulse supplied from input 5 of gate D406b to input Cl of 6D flip-flop D4 07, more specifically flip-flop D407 assumes the position of counter D408, while maintaining said position on the respective of the outputs D9, D7, D5, D3 and D1 until the later, positive edge of a read pulse appears. In other words, when subscriber station telephone set No. 1 has been selected, output D9 leading to telephone set switching circuit TGK1 will be constantly at one.

The resistor R413 and the capacitor C407 further form a delay circuit by means of which a reset pulse which is linked to a pulse train is delayed in relation to a reset pulse which is supplied directly to the input 6 of the gate D406b, in such a way that at the output of the gate D406b a differential pulse with a duration of approx. 1 ms, with the help of which the counter D408 is precisely zeroed

to emit new selection pulses.

The above-mentioned blocking signal produced by a respective one of the input flip-flops, such as D401b, is also supplied to input 1 of the gate D406a, so that the counter D408 is reset automatically also after completion of a pulse train cycle.

The aforementioned input blocking is likewise operative on the output circuit's D407 reset input R, so that this memory is also reset automatically.

As already discussed above, an output signal produced on one of the outputs of the output memory D4 07 is operative via the respective telephone set connection circuit for energizing the ring signal relay K202 for the internal ringing, for the called subscriber station telephone set. Fig. 9 shows a set of waveforms A-f which illustrate the operation of the selection register described above. Fig. 9A shows (viewed from left to right in the drawing) a rest interval 1, a set of selection pulses 2 and a reset pulse 3 which are supplied to the counter's D418 input 14. Fig. 9B shows the waveform of the corresponding signal which is developed via the capacitor C4 06 , but the resulting signal on port D406a output 3 is shown in fig. 9C. Fig. 9D shows the waveform of the signal which is supplied to the input 9 of the output circuit D4 07 and which is generated on the spot as a result of the signal developed via the capacitor C407 (Fig. 9E). The signal formed at the output of gate D4 06b is shown in fig. 9F. This signal is produced as a result of the signals shown in fig. 9A and 9E. During the time interval t1~t2, the selection pulses are counted by counter D408. At time t3 (positive edge of the pulse shown in Fig. 9D), the position of the counter D408 is supplied to the D407 input of the output circuit, and this information is transferred to the circuit's outputs. This information remains in place until the subsequent pulse (Fig. 9D-) occurs. The aforementioned output information does not change when it appears from the following pulse (fig. 9D) that the counter D408 is in the same counting position, as this information offered at the output circuit's D407 inputs is then the same as in the previous reading.

At time t^ a reset operation begins.

Fig. 10 shows a further detailed connection diagram of the base unit BED which is also connected to the central processing unit and which forms a connection between the insertable printed circuits, such as the telephone set connection circuits, the telephone line control circuit and the selection register.

The base unit, which is also arranged on a

printed plate, further comprises the signal generator for the optical signaling (18 kHz), the power for the voice circuit, the power for the signaling emanating from a subscriber station telephone set, the power for the aforementioned signal generator for the optical signaling, the power for the integrated circuits and the associated relays, the effect for the acoustic signaling, the holding relay K502, the mains voltage monitoring relay K501 and contact closures and protection devices.

The supply system transformer is arranged outside the printed circuit board.

Said signal generator comprises an operational amplifier D502, capacitors C504 and C505 and a resistor R515 being frequency-determining parts. Two diodes V506 and V507 connected in anti-parallel form an amplifier arrangement with resistors R503, R505 and R506.

When a start signal which is operative for the signal generator is received via a resistor R501, the oscillation, as the input C23 then gets a zero level, will increase relatively slowly to full amplitude, so that no switching spikes or unwanted disturbances will occur. Likewise, the gain will gradually decrease when the signal generator is switched off. The connection time is 250 ms and the disconnection time is 300 ms. The sine signal with a frequency of 18 kHz produced by the signal generator is power amplified by means of an amplifier D501 and a counter clock output stage with two transistors V501 and V502. Together with the tuned circuit that was processed in connection with the telephone set switching circuit (resistor R219, inductor T202, capacitor C209) the signal path of the aforementioned sine wave of 18 kHz provides such a high frequency attenuation that unwanted radiation is prevented.

The speech circuits that serve for internal traffic in the telephone system are fed from a conventional power source which - based on a supply system voltage of 220 V - has a minimum voltage of 4 9 V. When the mains voltage increases, the said voltage will be limited to a value of 51 V.

The transformer T502 provides a high impedance to the AC voltage component and likewise transforms the ring voltage so that an acoustic call is also audible at the calling subscriber station telephone set to verify that the called subscriber station telephone set is receiving ring power. Zener diodes V508, V509, V514 and V515 limit inductive spikes that could be produced during the internal connection in the event of dial operation.

The base unit also includes a supply part with a view to the signaling emanating from a subscriber station telephone set, and the electronic part of such a subscriber station telephone set. The aforementioned supply part comprises the integrated circuit D503 and transistors V526 and V504 by means of which a stabilized voltage of 27 V is supplied. The aforementioned voltage output is high-frequency coupled by means of capacitors C508 and C511. A limited integrated circuit supply of 33 V is thereby provided, while the voltage of 27 V is stabilized to a current value of approx. 500mA. Two resistors R521 and R522 act as current limiting devices, and two resistors R524 and R529 determine the supplied voltage.

Since the operational amplifiers and the counter clock output stage of the signal generator for generating the signal voltage with a frequency of 18 kHz require a positive-negative supply, the available voltage of 27 V is divided by means of a voltage divider formed by two resistors R520 and R528.

At the connection point between the mentioned resistors, a voltage of 13.5 V is thus produced which can serve as a zero level for the supply to the signal generator, so that in relation to the mentioned zero voltage a voltage of -13.5 V and a voltage of +13 are available .5 V. With the help of capacitors C508 and C511, it is achieved that the circuit has a minimal internal impedance for the supply part that serves as a signal generator.

The supply required for the integrated circuits and relays is provided by means of a supply section with an integrated circuit D504 and a transistor V505. The supply voltage produced by the aforementioned supply part has a magnitude of 10 V and is stabilized within a range of 0.2 V

at a current consumption between 0 and 250 mA. The maximum source voltage is thus only 1.3 mV. Together with a high-frequency suppression circuit with capacitors C514 and C513, this part of the supply power suitable for the integrated circuits is made available. As long as the voltage of 10 V is present, as already mentioned, the mains voltage monitoring relay K501 is energized, while this relay, in the event that the mentioned voltage disappears, has a switching function that has already been mentioned before.

If the mains voltage were to be interrupted, the relay contacts k501 and k'501 would therefore connect the voice wires for subscriber station telephone set no. 1 directly to the telephone line, so that said subscriber station telephone set no. 1 can function as a normal telephone set even if the telephone system is inactive , so that calls coming in via the telephone line are signalled, so that calls to the public telephone exchange are made possible.

For the internal ringing signals, a bell or buzzer in the respective called subscriber station telephone set will produce an acoustic signal. The AC voltage (60 V) required for this signaling is derived from the supply system transformer. As the additional telephone line clocks are also fed from the said transformer in the event of a call coming in via the telephone line, 60 V is also derived for the winding T501. When the triac V311 is switched on the latter signaling, one side of the AC voltage source is likewise connected to the AC voltage terminals' zero conductor for 10 and 27 V. This zero point is chosen centrally on the printed board to avoid hum voltages.

All incoming and outgoing wires can be clearly arranged and connected on the base circuit board, more specifically the telephone line to ground, if there is one; the telephone line clock or telephone line clocks; the optical busy signaling from outside the telephone system; the five subscriber station telephone sets to ground, if any; and the mains voltage.

The four secondary windings of the supply system transformer T502 are protected by means of safety fuses F501, F502, F503 and F504.

The resistors R530 - R549 which are present on the base circuit board, cause the input lines to the various circuits to be kept at one level (10 V) so that the correct operation of the telephone system is ensured if one or more of the telephone set connection circuits should be absent.

The double zener diodes V528 - V533 protect the inputs to the cabling against extremely high voltages and lightning discharges.

A resistor R551 together with a capacitor C516 forms a filter by means of which disturbances which may be produced by one or more of the telephone line clocks are eliminated.

The supply system transformer</>is placed outside the printed circuit board on the base plate of a housing formed of plastic material. On the secondary side, four windings are fitted for the supply measures described above, while on the primary side a temperature limiter is fitted which disconnects at 115° C and which cannot be restored or reset. The power at 220 V and when the microphones of the subscriber station telephone sets are charged is 15 W.

1. Telephone system for private use for a number of subscriber stations or subscriber devices, where mutual or internal traffic between these subscriber stations can be terminated via a common intercom line, and external traffic can be terminated via a telephone line that is common to the subscriber stations, each of the subscriber stations being connected to a common processing unit which is designed to control and perform the switching and signaling functions required to handle external and internal traffic, characterized in that each of the subscriber station telephone sets which are part of the telephone system is designed to be called with a separate selection key which is assigned to such subscriber station telephone apparatus to be called, each subscriber station telephone apparatus comprising a control circuit which, in response to a single operation of one of its associated selection keys, produces an electrical selection signal which uniquely defines the identity of

a called subscriber station telephone apparatus in the system, and that each subscriber station telephone apparatus is further provided with an electrical pulse transmitter which is arranged to a) in response to such an electrical selection signal generate a sequence of selection pulses indicating the identity of the called subscriber station -telephone apparatus in the system, and to also b) providing an initial pulse having a predetermined width and preceding each such sequence of selection pulses, and a means serving to open and close a signaling circuit coupled to the central processing unit under the control of pulses produced by the pulse transmitter. 2. Telephone system according to claim 1, characterized in that the pulse transmitter comprises a clock pulse source for generating clock pulses each of which has a width which determines the width of the selection pulses, a main counter which can be set using the selected selection signal and which,

in response to a selection signal at its input, performs a number of counting steps corresponding to the value of the applied selection signal increased by one, and an auxiliary counter which, in response to clock pulses from the clock pulse source and also to an output

Claims (1)

signal from the main counter, controls the main counter's counting function in such a way that, by means of gate circuit devices for combining clock pulses and output signals from the main counter and the auxiliary counter, regardless of the operating period of a respective selection key, at least one complete pulse sequence consisting of a initial pulse and a number of selection pulses indicating it. respective,- called subscriber station telephone set, followed by an incomplete pulse sequence consisting of an initial pulse and a selection pulse. 3. Telephone system according to claim 1 or 2, in which each subscriber station telephone device is provided with a signal lamp, characterized in that each of the selection keys is arranged to also form a short-circuit arrangement for the signal lamp in the relevant subscriber station when pressed phone device. 4. Telephone system according to one of claims 1-3, characterized in that each subscriber station telephone set comprises a telephone set of normal construction which contains a speech circuit and a separate auxiliary unit which comprises the said selection keys, a telephone line selection key, a signal lamp, the said control circuit and the electric pulse transmitter, and in which current variations in the speech circuit of the telephone device and current variations caused by putting on and taking off the handset can be detected via an opto-coupler circuit in the auxiliary unit, so that the auxiliary unit depending on the said current variations is either connected or not operatively connected to the central processing unit via a two-wire signaling circuit. 5. Telephone system according to one of claims 1 - 4, in which the central processing unit comprises a signaling device for internal ringing, the signaling device comprising a selection pulse counter and is operative in response to a received selection pulse sequence to supply a switching signal for the subscriber's call - te.Lophone device which is characterized by the aforementioned selection pulse sequence, to a separate switching circuit which is connected to the respective called subscriber station telephone device, the switching circuit, in response to such a switching signal, disconnects the speech circuit from the respective called subscriber station telephone device and connects the device to a ringing signal generator that is common to all • subscriber station telephone devices, in order to produce an audio signal that characterizes internal ringing, characterized in that the output of the selection pulse counter (D408) is connected to a selection pulse memory (D407) of which one read signal input (9) is connected. a read signal/reset signal circuit (D406a, D406b, D409b) which is also connected to the selection pulse counter's reset input (15), the arrangement being such that in response to a read signal produced by the aforementioned read signal/reset signal circuit, a switching signal is produced on a separate output from the selection pulse memory, which output is indicated by the selection pulse counter's count, and each time after the end of a received selection pulse sequence, a reset signal is supplied to the selection pulse counter's and the selection pulse memory's reset inputs via the read signal/reset signal circuit. 6. Telephone system according to claim 5, in which the signaling device comprises a number of separate input circuits which can be connected via a gate device one at a time to the input of the selection pulse counter, characterized in that each input circuit comprises a controllable, bistable circuit (D401a, D401b, D402a, D402b ,D 403a) which, in response to selection pulses applied to the circuit, on the one hand switches gate circuit devices connected to the output of the respective controllable bistable circuit so that the selection pulses are able to reach the selection pulse counter input, and on the other hand, produces a blocking signal so that all the other bistable circuits block the path extending through the circuits of the select pulse counter. 7. Telephone system according to claim 6, characterized in that all outputs of the controllable, bistable circuits on which a blocking signal for the other of the bistable circuits can be produced, are connected to further gate circuit devices (D405a, D409b, D409c) by means of which, after completion of a reception of selection pulses, a reset signal is produced for the selection pulse memory and the selection pulse counter. 8. Telephone system according to one of claims 1 -7, in which the central processing unit comprises a telephone line control circuit which participates in the termination of telephone line traffic, which telephone line control circuit a) in response to connection of a. subscriber station telephone set to the telephone line, connects a first signal generator for producing an optical signal characterizing the busy condition of the telephone line to all two-wire signaling circuits connected to the subscriber station telephone sets in the system, thereby producing an optical signal characterizing such busy condition in said subscriber station telephone apparatus, and b) in response to a switching function in a subscriber station telephone apparatus by means of which the telephone line is switched to a hold state, a second signal generator couples to the first signal generator such that an optical signal characterizing the telephone line's hold state is emitted in all subscriber station telephone sets, characterized in that the telephone line control circuit is further arranged to, in response to a call signal received via the telephone line, connecting a third signal generator (D304d, D304c) to the first signal generator (D502, C504, R515, C505) to produce an optical signal characteristic of such a call coming via the telephone line, for the respective signaling circuits connected to the respective subscriber station telephone sets. 9. Telephone system according to claim 8, characterized in that a call signal that arrives via the telephone line is transformed via an opto-electric circuit (D302) into a start signal for the third signal generator. 10. Telephone system according to one of claims 1 - 9, in which the central processing unit for each subscriber station telephone device in the system comprises a separate connection unit which serves as an intermediate connection between such a subscriber station telephone device and the other parts of the central processing unit , characterized in that each intermediate connection comprises two controllable, bistable flip-flops (D203b, D203a) which are respectively included in a first voltage-sensitive circuit (V202) which reacts to voltage variations caused by switching functions of the associated subscriber station telephone set fork contact or internal ring selection pulses emitted from this telephone set, and in a second voltage sensitive circuit (V201) which responds solely to voltage variations caused by operation of the telephone line key in the associated subscriber station telephone set, which two flip-flops in combination control a telephone line relay which serves to establish connection with the telephone line, a holding relay for omko pinging of the telephone line to the hold position, and also blocking the other flip-flops (D203a), all depending on the control voltages supplied to the voltage-sensitive circuits. 11. Telephone system according to claim 10, characterized in that if a second control voltage, after operation of a subscriber station telephone set's telephone line key, is supplied to the second voltage-sensitive circuit during the period when the telephone set's microphone is lifted, it becomes the input of this circuit, second flip-flop (D203a) not switched, whereby the output signal from the andro flip-flop, in combination with the other control voltage, energizes a grounding relay (K301) to connect one or both voice wires in the relevant subscriber station telephone apparatus voice circuit to ground.