DE29820869U1 - Intercom system with two wires - Google Patents

Description

Bitron Video S.r.l., Via Torino 21 /b, 10044 Pianezza (TO), Italy

Two-wire intercom system

The present invention relates to an intercom system with only two wires to connect all internal intercoms to the external station.

Two-wire intercom systems, also called "bus systems," are intercom systems that use only two wires to connect internal intercoms, e.g. a line of internal intercoms in an apartment building to an external station, where the external station has a keypad for visitors to call a desired internal intercom. Therefore, the two wires must carry both the conversation or speech and other signals, such as a door opening signal.

Systems are already known that use only two wires to connect the external station to internal intercoms, and allow selective communication from an external intercom side to a desired internal intercom, as well as opening the street door from an internal intercom. In such systems, a switch block structure provided for each internal intercom will, upon receipt of a corresponding call ID code, connect the internal intercom to the external station, while the other internal intercoms that are not called are connected to the

both wires of the line remain unconnected. This switch, which is essentially a relay associated with a microprocessor to detect the call ID code, will remain on as long as the main unit is sending a certain operating current to both wires in the line. If the operating current fails, the switch block will open and disconnect the internal intercom. The supply of operating current will only be terminated if a call is not answered or if a conversation is terminated.

Other intercom systems that improve on the systems described above are also known. In particular, a comparison circuit located in their internal intercoms identifies all voltage-modulated codes and transfers them to the internal intercom microprocessor. The internal intercom microprocessor is also able to issue commands by modulating the voltage in the wires of the line to cause a higher current to be supplied when speech is present. In addition, the two connecting wires in the systems can be interchanged using appropriate diode bridges without jeopardizing the operation of the system.

However, careful impedance balancing steps are necessary to achieve the desired result due to the variety of intercoms connected during voice operations, as similar voice interference problems may arise. In addition, such systems also require the provision of each internal intercom with an appropriate identifying code. However, inserting an appropriate call ID code into each intercom of each apartment or location during system installation is a relatively complex and time-consuming operation, especially when performed in apartment buildings with many floors and therefore many intercoms.

Moreover, these problems do not solve the problem of supplying the working current. On the contrary - as mentioned above - they require an additional power source when the circuit is connected to high loads, such as a loudspeaker or an electric bell.

It is the main object of the present invention to solve the above-described drawbacks and to provide an efficient intercom system which uses only two wires to connect all internal intercom stations to the external intercom station.

It is a further object of the present invention to provide an intercom system in which internal intercoms are activated only during required steps.

It is a further object of the present invention to provide an intercom system with a simplified circuit during the speech step, which does not require impedance compensation.

It is another object of the present invention to provide an intercom system which has low power consumption.

It is a further object of the present invention to provide an intercom system which allows parallel connection of a large number of intercoms.

It is a further object of the present invention to provide an intercom system which is quick and easy to install, especially with call ID code programming. ,

In order to achieve these objectives, it is an object of the present invention to provide an intercom and/or an intercom communication procedure as defined in the appended claims, which form an integral part of the description.

Further objects, characteristics and advantages of the present invention will become clear from the following detailed description and the accompanying drawings, which are given as a non-limiting example, in which

Fig. 1 shows the block diagram of an intercom system according to the present invention;

Fig. 2 shows the block diagram of an external intercom station according to the present invention;

Fig. 3 shows schematically the signals sent from the external intercom station of Fig. 2 to the line;

Fig. 4 shows the block diagram of an internal intercom station according to the

present invention;

Fig. 5 shows a detailed circuit of the internal intercom station according to the present invention;

Fig. 6 shows another embodiment of the circuit of Fig. 5;

Fig. 7 shows another embodiment of the intercom system of Fig. 1. I

With reference to the above figures, Fig. 1 describes a basic diagram of an intercom system according to the present invention. It is clear that the intercom system SI comprises an external station PE connected to a call keypad KEY containing an electric street door lock AP, a transformer T. Two line wires LN connected to a plurality of internal intercoms Pl leave the external station PE, which is the unit where the user makes the calls through the keypad KEY. In addition, each internal intercom Pl has a corresponding call line on the floor P, i.e. for the call normally made at the door of the apartment to be visited, which is connected to a corresponding call identification key on the floor TP, in order to make the call on the floor using the bell of the internal intercoms Pl instead of an independent bell. The transformer T is used to convert 220 volt supply voltage into 1 2 volt and 24 volt voltages.

As can be seen, the call keypad KEY has a large number of switches TK that are able to close different circuits between some connections of the external station PE.

Fig. 2 shows the basic diagram of the external intercom station Pl. As can be seen, the external station PE is connected to the call keypad KEY. When one of the switches TK shown in Fig. 1 is activated, a corresponding signal is sent to an external microprocessor MPEXT. This external microprocessor MPEXT controls a three-stage supply block MAL, which is supplied with 24 volts by the transformer T through the two signals TX and TXI. The MAL block is connected to the two line wires LN leading to the internal intercoms Pl through a first circuit block SW1 and a second circuit block SW2, as will be described in detail later. Both the first circuit block SW1 and the second

Circuit block SW2 are each controlled by the external microprocessor MPEXT. The external microprocessor MPEXT receives its own 5 volt supply voltage from a power supply unit POW, which is also connected to the 12 volt output of the transformer T. In addition, the external station PE contains a speech block BF11 suitable for bidirectional communication, including a loudspeaker SP and a microphone MC, which are connected to their respective amplifiers A1 and A2. The amplifiers A1 and A2 are connected to a two-wire disconnect circuit, which is similar in function to a hybrid coil, also called a hybrid circuit F, to separate the two communication directions. Finally, the external station PE contains a reset and reset circuit IOR, which is connected to a reset line R and is controlled by the external microprocessor MPEXT and a door opener block BAP.

When in stand-by, the external station PE must generate a first stand-by voltage V1 on both LN lines, i.e. approximately 15 volts DC, which is used as stand-by voltage for all internal intercoms Pl. The diagram in Fig. 3, which represents the voltage-time diagram VLN on both LN lines, is now taken into account as a reference. This function is performed by the three-stage supply block MAL, which, based on the TX and TXE signals received from the external microprocessor MPEXT, is able to generate DC voltages of 1 5, 24 or 12 volt amplitude. During this step, the external microprocessor MPEXT will also light up the signal LED L1 green to indicate the operating status of the system.

Whenever visitors make a call, i.e. they press a key on the call keypad KEY which identifies the user they wish to call, the external microprocessor MPEXT will generate a suitable call ID code CODE according to the circuit closed by the switch TK of the call keypad CODE. Before sending the call ID code CODE, the external microprocessor MPEXT will turn the LED L1 red to indicate the call and will bring the voltage VLN to a 24-volt DC call voltage level V2 for approximately two seconds on both line wires LN, controlling the three-stage feed block MAL accordingly. This allows all internal intercoms Pl to light up. The external microprocessor MPEXT will then generate the call ID code CODE in digital form in pulses (approximately at a frequency of 1000 Hz), which varies according to the internal intercom to be called. Such a call ID code CODE will be five consecutive

Repeated times to ensure automatic correction of similar transmission or reception indifferences. The call ID code CODE has the form of a pulse chain which is then sent to the two line wires LN with approximately 23 volts peak-to-peak voltage (1.2 to 24 volts), as can be seen from Fig. 3.

During this step, each internal intercom Pl compares the call ID code CODE transmitted with an appropriate identifying code PCODE, and only the internal intercom Pl involved will activate its own bell. During a further three-second interval, the three-stage supply block will again generate a supply voltage of approximately 24 volts in order to supply the required voltage to the internal intercom Pl that is to ring.

After these three seconds, the external microprocessor MPEXT will switch the signal LED L1 to yellow light to signal the switch to voice. The execution command is transmitted to a relay RL1 contained in the second switch block SW2, which causes the disconnection of the three-stage supply block MAL from the two line wires LN to connect the voice block output BF11. The three main functional elements of the voice block BF11 are the two amplifiers A1 and A2 required to feed the audio signals of the microphone MC, the loudspeaker SP, and the hybrid circuit F, which essentially consists of a transistor Q4 whose main function is to prevent the audio signal generated by the microphone MC from reaching the amplifier input A1, thus enabling a bidirectional conversation using only two system lines, i.e. the two line wires LN.

According to this operating configuration, a voice voltage level VF remains on the line wires LN until the called user responds. The voltage level VF consists of a direct voltage of about 1 2 volts, which is also taken from the power supply POW, the voltage drops to about 8 volts modulated voltage VFN, with a superimposed voice modulation, when the conversation between the internal intercom Pl and the external station PE starts. The conversation time is limited by the external microprocessor MPEXT, which supplies the relay RL1 with power for about one minute. However, it is switched off by the door opener block BAP when the user activates the electric lock AP of the door. This automatic switch-off can

by switching a special switch JP2, which is provided within the external station PE.

When the door release key P1 of the internal intercom Pl is pressed, the two LN wires are short-circuited and the VLN voltage drops to an opening voltage level VAP of about one volt. This opening voltage level VAP is detected by a voltage comparator CMPAP inside the door opening block BAP, which activates the timer TIM, which drives a relay RL3, which activates an opening of the electric door lock AP. When the switch JP2 is closed, a signal from the opened electric door lock AP is also sent to the external microprocessor MPEXT, which immediately deactivates the relay RL1 and restores the stand-by condition, i.e. the stand-by voltage on both LN wires.

The first circuit block SW1 and the reset block lOR are used to achieve multi-input systems connected to a plurality of external stations PE according to an on-off configuration as described in Fig. 6.

The first circuit block SW1, which essentially consists of the relay RL2 driven by the external microprocessor MPEXT, is connected to or disconnected from the line wires LN only when the external station makes a call.

The reset and switching circuit lOR outputs a positive voltage to the reset line when a call is made to the external station PE. This voltage, which is maintained during the entire conversation time, is sent to all other external stations connected in parallel with the external calling station PE. It is also sent through the same reset and switching circuit lOR to any external microprocessor MPEXT, which will block the call possibility and which will cause the LED L1 to flash red, i.e. provide a "busy" signal.

The external microprocessor MPEXT causes the LED L1 to flash red even if a switch TK on the call keypad KEY remains blocked in its closed position for more than two minutes, i.e. signals a fault condition.

All other power supplies for the circuit (1 2 volt or 5 volt DC) are provided by power supply unit POW, which can supply both 12 volt and

5 volts DC voltages are generated as required for the operation of the circuit. provided.

Fig. 4 shows the block diagram of an internal intercom system Pl according to the present invention.

As can be seen, both line wires LN are connected in parallel with a diode bridge DBR to prevent polarity inversion, with a comparator block CMP, an analog switch block 2 and a tone buffer block TON connected to a bell S, and with an internal switch block SW. The comparator block CMP essentially contains a Zener comparator circuit DZ and is connected between the two line wires LN and the control input of the analog circuit block 2, the latter being connected to a supply block AL through a filter RC. The output supply block AL supplies 5 volts voltage VAL to an internal microprocessor MP. The analog circuit block 2 essentially contains a transistor Q2, which is also connected between the two line wires LN and the control input of the power supply block AL. The drive or base electrode of the transistor Q2 is, however, connected to an output 02 of the internal microprocessor MP. The internal circuit block SW is designed to connect the two line wires LN to an audio transducer block TRASD and is activated by lifting the microphone. The audio transducer block TRASD fits into the microphone audio section of the internal intercom Pl; it contains an internal loudspeaker SPI and an internal microphone MCI. The audio transducer block TRASD is connected to a door opener push button PI, which is designed to short-circuit the audio transducer block BAP, as detailed with reference to Figs. 2 and 3. Between the audio transducer block TRASD and the ground there is a circuit block 3 with an SCR diode, the control electrode of which is controlled by an output 03 of the internal microprocessor MP.

The internal intercom Pl also includes a programming unit PRG, maintained by an EEPROM memory, and a call interface block IN on the floor, connected to a call line P on the floor.

The function of the call interface block on the floor IN is to prevent the operation of the call button TP on the floor connected to the call line P during the conversation, i.e. the

Voice connection with the external station PE when the voltage VLN on both line wires LN reaches the modulated voice voltage level VFM.

Finally, a learning switch JP1 is provided, connected to an input I6 of the internal microprocessor MP, to allow the identification code PCODE to be entered into the programming unit PRG, as explained in more detail below.

Each internal intercom system Pl should fulfil the following functions:

- Detecting the call voltage level V2 of the external station PE and generating a call tone through the tone buffer block TON;

- Activation of the audio transducer block TRASD, which enables a completely secret bidirectional conversation with the PE remote station through the voice block BF11 and the circuit block SW2;

- possible sending of the door opening signal to the external station PE through the door opening block BAP;

- Generating a second ring tone when a bell button is pressed on the floor that activates the floor call line P;

- Allow connection to the LN conductors through the DBR diode bridge, without having to take polarity into account.

Accordingly, the internal intercom system should:

- have a very high impedance in standby mode so as not to unbalance the overall impedance of the circuit;

- Extracting the energy supply required for the operation of the internal microprocessor MP from the signals on the line wires LN;

- Detecting the call ID code CODE that has been transmitted and comparing it with its own identification code PCODE (assigned by storing it in the programming block PRG);

- Connecting the audio transducer block TRASD to the external station PE, or

Disconnect, having a very high impedance depending on whether the call is directed to it or not;

- Generating different ring tones used to identify the calls from the external station PE from those made on the apartment floor.

When in stand-by mode, the external station PE supplies both line wires LN with the 1 5 Volt stand-by DC voltage level V1, which can be connected to the internal intercom Pl without considering the polarity, thanks to the availability of the diode bridge block DBR.

Under these conditions, both the comparator block CMP and the analog circuit block 2 and the circuit block 3, which contains the SCR diode SC1, are open circuits, as a result of which all internal intercoms do not work, but are in stand-by mode.

Whenever visitors make a call, i.e. they press a button on the call keypad KEY, identifying the user they want to call, then the external station PE will send the 24-volt DC call voltage level V2 for about two seconds.

The comparator block CMP is able to detect that the input voltage has exceeded a threshold value of 17 volts. When this threshold is exceeded, as can be better seen with reference to Fig. 5, the transistor Q2 becomes conductive and therefore allows the voltage to reach the power supply unit AL, which is then able to generate 5 volts direct current, as necessary to power the internal microprocessor MP. During this step, the current consumption of each internal intercom Pl is kept extremely low (less than 8 mA), for example to allow a maximum number of 1 to 28 intercoms to be connected in parallel.

At the end of the two second time interval, the external station PE transmits the call ID code CODE, i.e. a digital square wave code of about 23 volts peak-to-peak amplitude, which is recognized, built up and sent to the internal microprocessor MP by the comparator block CMP through its Zener comparator circuit DZ. The internal microprocessor MP will compare the call ID code CODE which it has received with the exact identifying call ID code

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PCODE and if they match it will:

- activate the analog circuit block 2 to ensure the power supply for the internal microprocessor MP even if the voltage VLN on both wires LN reaches the voice voltage level VF, which is lower. Due to the clipping Zener circuit DZ, the comparator block CMP will correspond to an open circuit;

- a call tone is generated, suitably amplified by the tone buffer block TONE and sent to the loudspeaker SPI of the internal intercom Pl, contained in the audio transducer block TRASD;

- through its output 03 the activation signal for the gate of the SCR diode SC1 in the circuit block 3 is supplied.

The activation signal lasts for about 40 seconds. During this entire period, the user can respond simply by picking up the microphone; this situation is achieved by switching the internal circuit block SW. Once the SCR diode in the circuit block 3 has been started by the control supplied by the internal microprocessor MP through its output 03, it will, by its own nature, remain in the conductive state as long as the current flowing through it is not interrupted and will operate through the internal circuit block SW, subsequently disconnecting the audio transducer block TRASD from the external station PE. The internal microprocessor MP provides an input 11 suitable for detecting the lifting of the microphone, which activates the switching of the circuit block SW; as a consequence, the internal microprocessor MP switches itself off by activating the analog circuit block 2 in a correct manner, e.g. by removing the bias from the base electrode of the transistor Q2 so as not to load the two line wires LN with their own impedance. Therefore, the conversation is ensured by the circuit block, since the SCR diode SC1 remains conductive until the microphone is hung up again and the internal circuit block SW is switched.

The P1 push button allows the two LN wires to be short-circuited, while the voice is activated, in order to supply the external station PE and, in particular, to supply the door opening block BAP with the opening voltage VAP, which acts as a door opening control.

The circuit of the internal intercom system Pl will now be described in more detail with reference to Fig. 5.

The diode bridge DBR consists of 4 Schottky diodes of type 1N5819, which allow a maximum limitation of the series voltage drop to be achieved, but which allows the system lines to be connected without regard to their polarity.

The comparator block CMP essentially consists of a transistor Q5 and a Zener diode DZ1, which form the Zener comparator circuit DZ. The Zener comparator circuit DZ is a well-known circuit; as described above, its insertion into the internal memory circuit Pl allows the electrical connection of the intercom circuit Pl to the two line wires LN only when the input voltage exceeds 18 volts, i.e. when the Zener voltage of the Zener diode DZ1 exceeds 18 volts. Therefore, thanks to the comparator block CMP, the internal intercom Pl can switch itself off when the standby voltage V1 only reaches 15 volts under standby conditions.

When the input voltage of the comparator block CMP is below 18 volts, the Zener diode DZ1 does not conduct and causes the transistor Q5 to enter a cut-off state.

In contrast, if the input voltage to the comparator block CMP exceeds 18 volts, the Zener diode DZ1 will conduct and saturate the transistor Q5.

The transistor collector Q5 is connected to the analog circuit block 2, in particular to a transistor collector Q4 which is essentially the base of the transistor Q2 of the PNP type. The saturated transistor Q5 brings the transistor collector Q4 and the transistor base Q2 to ground. Therefore, the transistor Q2 will saturate a 5 volt stabilizer, e.g. a stabilizer LM 2931, and will leave the voltage VLN on both line wires LN to be sent to the power supply input AL through the filter RC. The power supply unit AL is therefore able to provide voltage VAL to the internal microprocessor MP. During reception of the call ID code CODE, the Zener diode DZ1 is either conducting or in the cut-off state, causing the transistor Q5 to be saturated and cut off. As a result, the following advantages occur:

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- the call ID code CODE received can be obtained from the transistor collector Q5 and can be sent to an input I2 of the internal microprocessor MP;

- since the transistor Q2 will also be saturated and turned off, according to the same trend imposed by the call ID code CODE, when its base is connected to the transistor collector Q5, the dynamic impedance during reception of the call ID code CODE of the internal intercom Pl is higher and allows the connection of a higher number of devices in parallel.

During the turn-off phases of the transistor Q5, which should generally not be longer than 1 millisecond, the power supply to the internal microprocessor MP is ensured by the filter RC, which consists of a capacitor C6 and a resistor R28. The analog circuit block 2 is also used to ensure the required power supply for the internal microprocessor MP after the validation call has been recognized. The internal microprocessor MP will in fact saturate the transistor Q4 and therefore also the transistor Q2, which brings its own output 02 to a higher logic level. Now the power supply unit AL can receive the voltage VLN on both line wires LN, even if the voltage level on the line LN drops below 18 volts, i.e. the voltage level of the voice voltage VF. The condition described above occurs after the internal microprocessor MP has detected the call ID code CODE, recognized it as consistent with the identifying call ID code PCODE, and then activated an appropriate internal timer to 40 seconds, during which the user can lift the microphone and answer the call.

After 40 seconds have elapsed, or when the user answers the call, the internal microprocessor MP must disconnect itself from the LN line by switching off its own supply block unit AL to avoid the voice circuit impedance becoming unbalanced. This is obtained by simply bringing the output 02 to the logic level "zero". During the shutdown step, the supply voltage for the terminals of the internal microprocessor MP gradually goes down to zero.

The tone buffer block TON consists essentially of the transistors Q1, Q6 and Q3, which generate the signal generated by the internal microprocessor MP on the output 01.

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receive sound and amplify it. A push button SW3 is also provided to select whether the signal to be applied to the transistor base Q7 should be taken directly from the transistor collector Q3 (so that all available energy is used) or whether it should be taken from the rotor of a variable resistor RV1, which allows a high degree of adjustment.

The internal microprocessor circuit MP contains:

- an integrated microprocessor U1, which manages the information coming from outside;

- an integrated circuit U2 suitable for continuously monitoring the voltage supply to the terminals of the microprocessor MP U1 and for supplying it with a reset pulse as soon as the supply voltage falls below a value of 4.5 volts, so as to avoid possible malfunctions of the microprocessor U1 due to insufficient voltage;

- a quartz oscillator QZ to supply the integrated microprocessor with a clock signal with a frequency of 10 MHz.

Furthermore, a programming block PRG, consisting of a non-volatile EEPROM memory containing the specific call ID code PCODE of the internal intercom Pl in question, is closely linked to the operation of the internal microprocessor MP. In a possible embodiment, the programming block PRG is obtained by a block of selection switches, the so-called dip switches, the states of which determine the specific call ID code PCODE.

The switching block 3, which contains the SCR diode SC1 as mentioned above, is the block that receives the command from the output 03 of the internal microprocessor MP on its own control electrode, which will connect and keep connected the audio transducer block TRASD on the external station PE to allow a conversation even if the internal microprocessor MP is no longer powered.

In fact, the SCR diode SC1, once started by the command from the output 03 of the internal microprocessor MP, remains conductive until the current flowing through it is stopped, such as when the internal

Circuit block SW is disconnected from wire LN after hanging up the microphone.

Finally, the call interface block IN on the floor essentially contains a transistor Q8 and two Zener diodes DZ3 and DZ2, each providing a Zener voltage of 12 volts.

In addition, a diode D2 and a resistor divider with resistors R6 and R7 are provided, which connect the call interface block IN on the floor to the internal microprocessor MP. Also, a diode D12 and a resistor R14 are provided to connect a call interface block IN on the floor to the transistor base Q2 of the analog circuit block 2. The Zener diode DZ2 is connected to the wire LN, whereby when the voltage VLN on both line wires LN 1 exceeds 2 volts, such as when it receives the standby voltage level V1, the Zener diode DZ2 is conductive and will saturate the transistor Q8, which is connected to it through the base electrode. Under this condition, a short circuit to earth is carried out in which the call line P on the floor is short-circuited by the floor call button TP, which sends an earth signal both to the input I4 of the internal microprocessor MP, passing through the diode D2, and to the transistor Q2 through the electrical path passing through the diode D1 2. The transistor Q2 is then saturated similarly to when excited by the transistor Q5 and it enables the operation of the power supply unit AL. The internal microprocessor MP is enabled to recognize the earth signal on the input I4 as representative of a floor call, and it activates the tone buffer block TON through its own output 01 with a different ring tone than it used for the call from the external station PE.

Vice versa, if a modulated voice voltage level VFM is present on both line wires LN, the Zener diode DZ2 is switched off due to its Zener voltage of 1 2 volts, i.e. a voltage higher or equal to that available on the line wires LN, with a subsequent switching off of the transistor Q8. A short circuit on the floor call line P caused by the floor call button TP will, under this condition, neither set the transistor base Q2 nor the input of the internal microprocessor MP to earth, since the voltage level is that forced by the Zener diode DZ3, i.e. the floor call button TP is blocked.

In summary, the SI intercom system described above works as follows.

In standby mode, all internal intercoms Pl are blocked, so that none of them are supplied; the two line wires LN have a direct voltage of about 15 volts, i.e. the standby voltage level V1.

Whenever users make a call by pressing the key on the keyboard KEY corresponding to the user they wish to call, the external microprocessor MPEXT contained in the external station PE will send a call voltage level V2 to the line LN, i.e. about 24 volts for two seconds to cause all internal intercoms Pl to be switched on. This will then be followed by the call ID code CODE, i.e. a digital code with about 1000 Hz frequency and about 23 volts peak value, as explained above.

During this step, each internal intercom Pl compares the call ID code CODE that was transmitted with its own call ID code PCODE, and only the internal intercom Pl in question will activate its own ringing. The subsequent three seconds after receiving the call ID code CODE, during which the call voltage level V2 with 24 volts DC is available, are used to provide the required supply voltage to the internal intercom Pl, which will ring. After these three seconds have elapsed, all internal intercom Pl are disconnected from the system, while only the one called is connected to the external station PE. During the conversation, the connection is in fact ensured by the SCR diode SC1 which maintains the connection and which allows the remaining circuit section, in particular the internal microprocessor MP, to go out so as not to influence the impedance of the voice circuit, which is still formed by the audio transducer block TRASD connected by the two line wires LN to the voice block BF11 in the external station PE.

During this speech step, the external station PE will disconnect the standby voltage V1 from the system lines via the relay RL1 in order to connect the speech block output BF11, which can ensure bidirectional conversation with only two wires.

As long as the called user does not answer, the two line wires LN of the system will have the voice voltage VF, i.e. a direct voltage of about 1-2 volts, which drops to about 8 volts, with superimposed modulation for the modulated voice voltage level VFM when the internal intercom Pl answers. The duration of the conversation from the external station PE is limited to about one minute, but is terminated when the user activates the electric door lock AP.

When the door release button P1 is pressed, the two line wires LN are short-circuited and the voltage VLN drops to the opening voltage level VAP of about 1 volt. The voltage comparator CMPAP inside the external station PE will register this event and will enable the timer circuit TIM to activate the electric door lock AP. The intercom system SI then goes directly back to standby.

Each internal intercom Pl is also equipped with the call line P with two connections on the floor, to which the corresponding floor call button TP must be connected. When the floor call button TP is pressed, the internal intercom Pl will have a ring tone different from the standard tone to signal a call from the floor.

During the conversation with the external station PE, the two line wires LN will be activated to carry the conversation represented by the modulated voice voltage level VFM and will not allow to accept a supply voltage of adequate value. For this reason, during this time the floor call buttons TP must be blocked. This is done - as described above - by the call interface block IN on the floor.

The programming block PRG consists of a non-volatile EEPROM memory, which contains the internal intercom Pl’s own call ID code PCODE.

This programming block PRG is provided with a self-loading function of its own call ID code PCODE, which is activated during the final installation step of the system. The self-loading operation is carried out by activating the external call key on the call keypad KEY to pair with the internal intercom Pl and, together with a corresponding learning key, it adapts itself to the self-learning switch JP1 in

the internal intercom system Pl.

By inserting the self-learning switch JP1, the ground is supplied to both the analog circuit block 2 which supplies ground to the internal microprocessor MP, and to the internal microprocessor MP itself as a signal to perform the self-learning function. Under this condition, the internal microprocessor MP will then switch to the SCR diode SC1, allowing voice communication with the external station PE during the self-learning operation. During this step, the program controlling the internal microprocessor MP causes the call ID code CODE to be stored directly in the EEPROM memory of the programming block PRG as its own call ID code PCODE. Finally, to confirm that the storing has been carried out, the internal microprocessor MP is programmed to generate a store confirmation tone using the tone block TONE, which can be superimposed on the voice signal when a conversation takes place between two hypothetical installers, or transmitted by one alone.

It should be remembered that the switch JP1 remains closed only during the self-learning operation of the call ID code CODE, while it must be left open during the standard operation after installation, i.e. the element that shorts the terminals of the self-learning switch JP1 must be removed. Therefore, the element is chosen that has a suitably large housing to mechanically interfere with the closing cover of the internal intercom P1, preventing its closing when in position. There is thus no probable possibility for the installer to forget the self-learning switch JP1 closed, which would result in the learning of every call ID code CODE that would be subsequently sent. With the above solution, in fact, it is not possible to close the housing of the internal intercom circuit Pl.

The call ID code CODE is then stored in the EEPROM memory as a separate call ID code PCODE. It should be remembered that due to the fact that an EEPROM memory is used, i.e. an erasable and rewritable memory, the programming block PRG can be reprogrammed by repeating the same procedure.

In a simplified embodiment, the unique call ID code PCODE is assigned to each internal intercom Pl by a special dip switch unit, which

is located within the internal intercom system Pl itself.

Fig. 7 shows the same intercom system SI of Fig. 1, but with a higher number of external stations PE in order to illustrate the connection between a large number of external stations PE.

In this case, in each external station PE it will be sufficient to use the switching device consisting of the first switching block SW1 and the reset and switching circuit IOr as shown in Fig. 2. The switching device will recognize a call made and automatically connect the external station PE called to the line. The various external stations PE shown in Fig. 7 are connected to each other in an on-off configuration, safe for the first external station PE which keeps the system in stand-by condition and whose first switching block SW1 is used exclusively to indicate a busy state. Connections between each external station PE make use of three non-reversible wires, one of which corresponds to the reset line R and the other two to the two line wires LN.

Finally, Fig. 6 shows a possible variation of the comparator block of Fig. 5, in which a comparator block CMP' is shown, which is obtained by a voltage detector circuit VDET. This voltage detector circuit VDET, e.g. an integrated circuit S80745 from SEIKO, corresponds functionally to a comparator with a hysteresis, and similarly to the comparator CMP, will hold the transistor base Q5 to ground when the voltage VLN drops below 18 volts and drive the transistor Q5 into saturation when the voltage VLN exceeds 18 volts. The use of the voltage detector circuit VDET instead of a Zener diode allows a more precise turn-on threshold as well as an "on-off" control of the transistor Q5 instead of linear variations of the control voltage due to the use of a Zener diode. It should be additionally clear that the voltage detector circuit VDET is connected downstream of the Zener diode DZ2 belonging to the call interface block IN on the floor. Therefore, the voltage detector circuit VDET as well as the call interface block IN on the floor are safely excluded when the two line wires LN have either the voice voltage VF or the modulated voice voltage level VFM.

The characteristics of the intercom system described above and in the accompanying drawings will now be clear.

According to the above description, the advantages of the intercom system, which are the object of the present invention, are now also clear.

In the intercom system according to the present invention, each intercom installation advantageously comprises a comparator circuit capable of detecting a call voltage level sent by the external station and also capable of controlling activation of the entire intercom circuit and in particular of its microprocessor. On the other hand, the comparator circuit is advantageously the same as that used for call ID code demodulation.

According to the present invention, it is also possible to completely disable the intercom stations where the call ID code does not match. Therefore, intercom stations that have not been called are only connected to the line wires during the steps related to the call that has been sent and to the relevant call ID code.

In addition, the selected intercom will automatically exclude a section of its own circuit, namely its own microprocessor during the conversation, leaving only the audio transmission section connected to the line wires.

This is a great advantage during the conversation, as

- a simple cradle-type circuit can be used in the external station to support a conversation with the internal intercom alone activated;

- since the audio transmission section is the only impedance available on the line wires, circuits with complex adaptation or impedance compensation are not necessary.

A further advantage is represented by the possibility of easily programming the individual call ID codes for each internal intercom during installation through a self-learning technique that provides insertion of the call ID codes directly from the external station keypad.

A further advantage is also ensured by the possibility that this operation can be repeated many times using a non-volatile EEPROM memory.

It is clear that many changes can be made to the intercom system described above by way of example by a person skilled in the art without departing from the novel spirit of the innovative idea, and it is equally clear that in the practical implementation of the invention the components shown in detail can often differ in shape and size from those described, and can be replaced by technically equivalent elements.

For example, the same call ID code can be assigned to two internal intercoms to enable parallel conversation with a single external station.

Claims (11)

¹ Hamburg, 10 December 1 998 Bremen Eisenführ, Speiser & Partner *· ·.:, . : ,·.*..!.··. Patent attorneys • · · · HafhBurg· European Patent Attorneys ·*· * *" Patent Attorney Our reference: B 2262 FM/nne Dipl.-Ing. Günther Eisenführ Dipl.-Phys. Frank Meier Dipl.-Ing. Dieter K. Speiser Dr.-Ing. Werner W. Rabus Lawyers Applicant/Owner: Bitron Video S.&Ggr;.&Igr;. Dipl.-Ing. Jürgen Brügge Christian Spintig Official reference number: New registration Dipl.-Ing. Jürgen Klinghardt Rainer Boehm Dipl.-Ing. Klaus G. Göken Jochen Ehlers Ballindamm 3 Patent attorneys D-20095 Hamburg New demands Dipl.-Ing. Mark Andres Phone +49-10)40-309 7440 Dipl.-Ing. Joachim von Oppen Fax +49-10)40-3097 4444 Lawyers mail@eisenfuhr.com Ulrich H. Sander Sabine Richter Munich Patent attorneys European Patent Attorneys Dipl.-Wirtsch.-Ing. Rainer Pritsche
Lbm.-Chem. Gabriele Leißler-Gerstl Patent Attorney Dipl.-Chem. Dr. Peter Schuler Berlin Patient lawyer European Patent Attorney Dipl.-Ing. Jutta Kaden Alicante European Trademark Attorney Dipl.-Ing. Jürgen Klinghardt 1. Intercom system comprising at least one central calling station (PE) and a series of remote terminals (Pl) connected to it by a two-wire electrical line (LN), the central calling station (PE) comprising multiple-level supply means (MAL) designed to supply the electrical line (LN) with at least a first stand-by voltage level (V1) and a second calling voltage level (V2) different from the first stand-by voltage level (VD), with setting means for a call ID code (KEY), with modulation means of the call ID code (MPEXT), the remote terminal (Pl) comprising audio transmission means (TRASD), a microprocessor (MP) associated with a supply (AL), a comparator circuit (CMP) whose input is connected to the electrical line (LN), suitable for demodulating the call ID code (CODE) and transmitting it to the microprocessor, characterized in that characterized in that the output of the comparator circuit (CMP) controls the power supply unit (AL) of the microprocessor (MP) and enables the operation of the power supply unit (AL) when the electrical line (LN) has the second call voltage level (V2). 2. Intercom system according to claim 1, characterized in that the second call voltage level (V2) is higher than the first standby voltage level (V1). 3. Intercom system according to claim 2, characterized in that an analog switching means (2) is provided, stimulated by the microprocessor (MP), which is suitable for setting the power supply unit operation (AL) of the microprocessor (MP) after an initial operating time. 4. Intercom system according to claim 3, characterized in that a switching means, stimulated by the microprocessor (MP), is provided, which is able to maintain the power supply of the audio transmission means (TRASD) when the microprocessor (MP) is switched off. 5. Intercom system according to claim 3, characterized in that the comparator circuit (CMP) controls the power supply unit (AL) of the microprocessor (MP) when energizing the analog circuit block (2). 6. Intercom system according to claim 5, characterized in that the comparator circuit (CMP) contains a Zener comparator circuit (DZ), the output of which is connected to the analog switching means (2) which excite the power supply unit (AL). 7. Intercom system according to claim 6, characterized in that the analog switching means (2) contain a first transistor (Q2) whose emitter is connected to the electrical line (LN) and whose collector is connected to the power supply unit (AL), excited by a logic signal emitted by an excitation output (02) of the microprocessor (MP). 8. Intercom system according to claim 6, characterized in that the comparator circuit (DZ) comprises a Zener diode (DZ1) and a transistor (Q5). 9. Intercom system according to claim 8, characterized in that the first transistor (Q2) of the analog switching means (2) is excited by the microprocessor (MP) through a second transistor (Q4), the second transistor (Q4) being connected with its base to the excitation output (02) of the microprocessor (MP), and the collector being connected both to the base of the first transistor (Q2) and to the collector of the transistor (Q5) of the comparator block (CMP). 10. Intercom system according to claim 4, characterized in that the switching means (3) are obtained by an SCR diode (SCD) connected between the audio transmission means (TRASD) and earth, and which are excited by a logic signal emitted at an excitation output (03) of the microprocessor (MP). 11. Intercom system with at least one central calling station (PE) and a number of remote terminals (Pl) connected to it by an electrical line (LN), the central calling station having setting means for a call ID code (KEY), modulation means for the call ID code (MPEXT), the remote terminal (Pl) having a microprocessor (MP) connected to a power supply unit (AL), and a comparator circuit (CMP), the input of which is connected to the electrical line (LN), designed to recognize a call ID code (CODE) consistent with a preset call ID code (PCODE), furthermore programming means (PRG) being provided to set the preset call ID code (PCODE) in the microprocessor (MP), characterized in that the programming means (PRG) consist of an electrically programmable, non-volatile memory, in particular an EEPROM memory, and by entering the preset call ID code (PCODE) into the electrically programmable, non-volatile memory, by sending the appropriate call ID code (CODE), by the call ID code setting means (KEY), by acting on a learning switch (JP1). 1 2. Intercom system according to claim 14, characterized in that the learning switch (JP1) in its closed position is designed to operate the analogue switching means (2) for the power supply of the microprocessor (MP), and to control the execution step of the self-learning function of the microprocessor (MP). 1 3. Intercom system according to claim 1 5, characterized in that the learning switch (JP1) in its closed position mechanically prevents closing of the housing containing the remote control (P1).