JPS5919519B2 - Hands-free calling method in button telephone equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hands-free calling system in a button telephone device.

Conventionally, hands-free response and communication when calling an extension in a button telephone device have been constructed using a circuit system, an example of which is shown in FIG.

In Figure 1, 1 is a counting circuit, 2 is a decoder, 3, 4,
16 is an amplifier, 5 is a hybrid circuit, 6 is a relay, 6
-1 is the contact, 7 is the transformer, 8 is the transistor, 1
0 is the power supply, . 11 and 13 are the contacts of the hook switch, 12
, 14 is a telephone communication circuit, 17 is a speaker, 18 is a microphone, 19, 20, 21, 22 is a cable, 10
0 is the main device side control circuit, 200 is the calling side telephone circuit, 3
00 is the called telephone circuit. Therefore, in the circuit example shown in FIG. 1, when the transmitter telephone 200 is raised and dialed, the dial pulse operates the relay 6 and continues its contact 6-1, and its state is counted by the counting circuit 1. The decoder 2 develops the red color and leads the output signal of its unique output terminal to the base of the transistor 8 to turn it on. As a result, the transmission signal from the calling telephone 200 excites the primary winding of the transformer 7 through the route [talk circuit 12 → switch 11 → cable 21 → hybrid circuit 5 → amplifier 4 → transformer 7], which excites the primary winding of the transformer 7. The induced output is input to the input terminal of the amplifier 16 via the route [secondary winding of the transformer 7 → cable 19 → earth E → "Ten source 10 → transistor 8 → secondary winding of the transformer 7]", The amplifier 16 amplifies and attenuates the speaker 17. Also, the telephone 3
The transmission signal from 00 is [microphone 18 → cable 2
0→Amplifier 3→Hybrid circuit 5→Cable 21→Hook switch 11→Telephone circuit 12]. With the above operations, the handset and receiver of telephone 200, and the speaker 17 and microphone 18 of telephone 300,
Each allows for phone calls. However, with this method,
It requires a cable 20 for transmitting microphone signals, and furthermore, since the call counting circuit 1 is locked, it is not possible to count other calls. In order to eliminate these drawbacks, the present invention has provided a telephone with a hybrid circuit, the main unit having a memory circuit for storing the counting results of the counting circuit, and a telephone line connected to the telephone line which is turned on by the output of the memory circuit. By connecting the switch means and the hybrid circuit via a communication line cable, it is possible to make hands-free calls, and the cables dedicated to transmitting microphone signals and speaker signals can be omitted. To provide a hands-free telephone call system in a button telephone device in which a circuit is connected to a called telephone and simultaneously opened to make effective use of the circuit.

The present invention will be explained in detail below using the drawings.

FIG. 2 shows an embodiment of the present invention, in which 1 is a counting circuit, 2 is a decoder, 51 is a relay, 51-1 is its contact, 30,
60 and 66 are the contacts of the hook switch, 29 and 58 are the telephone communication circuits (including the dial), 61 and 62 are the amplifiers, and 63
is a speaker, 64 is a microphone, 65 is a hybrid circuit 67, 68, 69, 72, 73, 74 is a cable,
56 is a flip-flop, 54 and 55 are analog switches (thyristor, etc.) compatible with telephones, 52 and 5
Reference numeral 3 indicates a telephone-compatible call switch control circuit composed of a shift register, etc., 57 and 59 are line control circuits, 75 is a transistor, 76 is an inverter, 101 is a main device, and 201
is a calling telephone, and 301 is a called telephone. During operation of the embodiment shown in FIG. 2, the line control circuit 57 includes means such as a telephone key, which is activated by operating it, and transmits its output signal to the main device 101 via the cable 68. Since the input is input to the call switch control circuit 52 and the output thereof is configured to open/close the analog switch 54, by raising the handset on the calling telephone 201 and operating the telephone key of the line control circuit 57, the above-mentioned route can be performed. analog switch 54
is closed.

Next, when dialing on the calling telephone 201, the dial impulse is [talking circuit 29 → switch contact 3]
0 → cable 67 → relay 51] route to relay 51
is operated, its contact 51-1 is turned on and off, and the counting circuit 1 counts it. This counting result is expanded by decoder 2,
One output terminal is input to the set terminal S of flip-flop 56, and its output is input to the gate terminal of analog switch 55, which is closed. As a result, the transmission from the calling telephone 201 is as follows:
The speaker 63 is sounded through the analog switch 55 → cable 72 → hook switch contact 60 → hybrid circuit 65 → amplifier 61 → speaker 63]. Also, the transmission from the called telephone 301 is carried out via [microphone 64 → amplifier 6
2 → Hybrid circuit 65 → Hook switch contact 60
→ Cable 72 → Analog switch 55 → Analog switch 54 → Cable 67 → Hook switch contact 30 →
The call circuit 29] is transmitted in a hands-free manner, and the call is received by the handset of the calling telephone 201. Further, the output signal of the flip-flop 56 is connected to the reset terminal R of the counting circuit 1, and the counting circuit 1 is reset by the output signal of the flip-flop 56. As a result, the counting circuit 1 can then prepare for another dial counting. Further, even if the counting circuit 1 is reset as described above, the above-mentioned communication state is maintained by the flip-flop 56. Next, the called party
When the telephone key included in the line control circuit 59 is pressed and the handset is raised in order to switch from a hands-free call to a call using the handset, the output signal of the flip-flop 56 is as follows: [cable 73 → switch contact 66 → cable 74 → flip-flop 56 is applied to the reset terminal R of flip-flop 56 to reset it.

At this time, the analog switch 55 is connected to the line control circuit as in the case of the calling telephone 201 described above. The output signal of 59 is input to the communication path switch control circuit 53 via cable 69, and its output is led to the gate of analog switch 55 and closed.

As a result, the communication between the calling telephone 201 and the called telephone 301 via the handset is carried out by [call circuit 29 → switch contact 30 → cable 67 → analog switch 54 → analog switch 55 → switch contact 60 → call circuit 58]. It is possible to connect by the route of . The overall operation of the present invention has been explained above.
57 → 68 → 52 → 54] or [59 → 69 → 53
→55] will be explained in more detail with reference to FIG.

FIG. 3 shows a call control system using a thyristor as the analog switch.

In FIG. 3, 501, 527 are counters, 502, 526 are clock pulse generators, 503, 504, 528 are decoders, 510, 581, 583 are inverters, 508,
511, 514, 515, 531 are AND gates, 50
7,509,512,532 is an OR gate, 513 is a shift register, 519,580 is a transformer, 529 is a telephone communication circuit, 530,536 is a hook switch, 53
3,534 is the contact point of the telephone key for selecting the central office line (or extension line), 53
5 is a power supply, 540 is a flip-flop circuit, 1 is the (G) side of the power supply, E is the (F) side of the power supply, 584 is a transistor, 554-1, 554-2 are thyristors, 585, 5
86,587 is a resistor. To operate the above circuit, it is assumed that counters 501 and 527 first count the output pulses of clock pulse generators 502 and 526, respectively, and that they are synchronized.
Now, in order to talk to the central office line, when the handset is raised and the telephone key for selecting the central office line is pressed, contacts 533 and 534 become connected. As a result, the timing pulse T'9 of the output signal from the decoder 528 driven by the output signal of the counter 527 is [decoder 528 → contact 533 → OR gate 532
->AND gate 531 -> flip-flop 540] is applied to the input terminal of the flip-flop 540. As a result of the above, the central office line (or extension line) is transferred from the telephone to the main device.
A signal for selection has been sent. The sent signal is received by the main device and stored in shift register 513. The timing for inputting to the shift register 513 will now be explained.

First, the counter 501 has a plurality of cascade-connected binary numbers.
A clock pulse generator 50 consisting of a counter
It is driven by the clock pulse train CP which is the output of 2. A time chart of the outputs C1 to ClO of the counter 501 is shown in FIG. Next, a decoder 503 and a decoder 504 are driven by the output of the counter 501 to obtain respective outputs t1-TO and Tl-TO. Ko\de T1~TO
is the output ClO of the counter 501, as shown in FIG.
This is a signal whose pulse width is the period of . Also, t1 to Tn are
As shown in FIG. 4, the signal has a pulse width equal to the period of CP, and the pulse width of t1 to TO is sufficiently small compared to the pulse width of T1 to. Furthermore, the signal T5 from the telephone
l~T'. 2 and 3 in Figure 4 between T1 and TO.
There is a relationship between them, and they are synchronized with a certain delay. FIG. 41 is a diagram showing the data timing in the case of five office lines, and in the figure, LK1 to LK5 indicate signals for the office line telephone keys, respectively. Y. T indicates a unit time with T1 to TO as time slots. As is clear from this figure, the transmission signal T'' from the telephone to the main device is
, is delayed by a certain period of time with respect to T9. This delay is for correcting the synchronization difference between the counter 501 and the counter 527 by receiving the signal near the center of the pulse width when the main device receives the signal. In FIG. 3, the flip-flop 540 is of a type that outputs an output at the rising edge of the gate pulse ClO.

Therefore, as described above, when the input signal T' is applied to this signal, it is output to the output side of the flip-flop 540 in synchronization with the gate pulse ClO, and is applied to one of the input terminals of the AND gate 511. The output signal at this time is ClO
Synchronize with. Here, ClO is the output of the counter 501. Next, the output of the shift register 513 forms a feedback loop in the loop of [output terminal of shift register 513 → AND gate 514 → OR gate 512 → input terminal of shift register 513], and the shift register 513 receives a clock pulse. The information shifted by the CP and inputted here is configured to be circulated and stored at a constant cycle. Therefore, in order to input the signal to the shift register 513, a timing pulse is output from the OR gate 509 by a circuit composed of an AND gate 508 and OR gates 507 and 509, and one output signal is sent to the AND gate 514 through an inverter 510. is applied and closes it. The other gate is applied to AND gate 511, and by opening it, the signal being applied from flip-flop 540 is input to shift register 513 through OR gate 512. Here, since this input timing is determined to be t1 and T2 as described above, the storage device in the shift register 513 is also fixed, and the signal is output at the timing of Tl and t2 one cycle later. In order to synchronize the input and output of the shift register 513, the storage capacity of the shift register 513 is set to be the same as the steps t1 to TO of one cycle of the decoder 503. As described above, the office line signal T' input from the telephone is converted to the timing Tl, t2, which is further processed by the AND gate 515.
With the pulse timing of C1, only t1 is activated, and its output is applied through resistors 585 and 586 to the respective gate terminals of thyristors 554-1 and 554-2, turning them on. Therefore, between the anode and cathode respectively [power supply 1 → resistor 587 → transformer 5
80 right winding → thyristor 554-1 (or 554-
2) → left winding 519-1 of transformer 519 → collector-emitter of transistor 584 → earth E], a direct current flows through the route of thyristor 554-1, 554-
2 is maintained in the on state, and the AC signal induced in the transformer 580 is transmitted to the transformer 519. Next, when the telephone key is pressed, for example, when the contact 533 of the telephone key changes from closed to closed, the input/output state of the shift register 513 changes.

That is, although the signal from the telephone is cut off, the shift register 513 stores a signal corresponding to the state of the contact 533 of the telephone key for one period, so the output of the AND gate 511 in FIG. The output of the shift register 513 is the corresponding time slot (in this case, T,,t
In 2), the former becomes a low level and the latter becomes a high level. The state is detected by an AND gate 582, and its output is applied to the base of a transistor 584 through an inverter 583. Here, when there is no input to the output terminal of the inverter 583, a high level, that is, a positive voltage is applied, and when a pulse is input to the inverter 583 in the above operation, its output becomes a low level, that is, the ground potential. As a result, the collector-emitter of the transistor 584 is turned off when the pulse is present, and the thyristor 554
-1,554-2 is cut off, and the thyristor 554-1,554-2 is turned off. Through the above operations, it becomes possible to control the communication path switch (thyristor switch) installed in the main device using the communication path control key, that is, the office line (or extension) telephone key installed in the telephone. The above operation has been explained for the operation when changing the telephone key, but this means that even if suddenly generated external noise etc. enters the control circuit and the erroneous communication path switch is closed, such a signal will not be removed. Since this is not continuous, the operation is similar to that described above, and the transistor 584 is momentarily cut off, turning the thyristor off.

In other words, it operates as an error detection function, and even if the communication path switch is closed by mistake, it will be opened after one cycle.Furthermore, by setting the cycle of the write control signal sufficiently short, this instantaneous misconnection can be practically avoided. It's not a problem. In addition, in FIG. 3, a case has been explained in which thyristors are used for the analog switches 54 and 55 in FIG. A similar effect can be obtained by inserting it between the base and the output terminals of the communication path control circuits 52 and 53.

In addition, in FIGS. 2 and 3, when the telephone 301 responds with a handset, the signal for setting the flip-flop 56 is branched from the cable 74 and is ORed to the input of the inverter 583 in FIG. By inputting this, the collector-emitter of the transistor 584 is momentarily disconnected, and the thyristor can be turned off in the same manner as the above-mentioned operation when changing the electric key.

In addition, in FIG. 2, a flip-flop is set at the set terminal R of the flip-flop 56, and a timer circuit that outputs an output signal after a certain period of time is connected in parallel, so that the hands-free calling is started after a certain period of time has elapsed after the start of the hands-free calling. Can be stopped. Next, the above explanation has been given regarding the power supplies of the amplifiers 61 and 62, assuming that they are already applied, but controlling the power supply so that it is applied when a calling signal is inputted also reduces power consumption, noise, etc. It is valid.

As an example of this control, an amplifier 6 is used as shown in FIG.
A transistor switch 75 is arranged at the power input terminals 1 and 62, and the output signal of the flip-flop 56 is transmitted to its base via the route [flip-flop 56 → cable 73 → inverter 76 → base of transistor 75]. When the output is at a high level, the base potential of the transistor 75 is grounded, its collector-emitter is turned on, and the amplifiers 61 and 62 are →Earth] power is applied through the route. Further, when the output of the flip-flop 56 is at a low level, the collector-emitter of the transistor 75 is disconnected through the route, and the power to the amplifiers 61 and 62 is cut off. With the above operation, it is possible to control the power of the amplifiers 61 and 62 to be turned on at the time of the call. In FIG. 2, the cables 73 and 74 are
By using the method shown in the figure, that is, the time division transmission method, the cable 69 can be shared and can be omitted.

Figure 3 shows the case where there is one line (or extension line) and one telephone line, but if there are multiple lines (or extension lines) and telephones, the thyristor switch It is sufficient to construct a matrix circuit in which the number of lines (or extensions) is multiplied by the number of telephones.

Figure 3 shows an example in which a thyristor is used as a communication path switch, but Figure 5 shows an example in which a thyristor is used in place of the thyristor, and an analog switch such as a transistor switch is combined with a memory element such as a D-type flip-flop. This is an example of a circuit. In this case, the D-type flip-flop is set only when there is an output signal from gate 515 in FIG. 3, and its output closes an analog switch to form a communication path.

Therefore, in FIG. 5, the output signal of the gate 582 in FIG. 3 is unnecessary. In FIG. 5, 601 is a D-type flip-flop;
02 and 603 are transistors.

Now, an output is obtained from the shift register 513 in the same manner as in FIG. 3, and is applied to the signal input terminal of the D-type flip-flop 601. On the other hand, by applying the signal of time slot T to its clock terminal, D-type flip-flop 601 is set, and its output signal is applied to the gates of transistors 602 and 603, turning them on. Through the above operations, a communication path is formed in the same manner as in FIG. 3. FIG. 6 shows an example of a circuit constructed by combining a transistor and an RS flip-flop circuit in place of the thyristor shown in FIG.
The output signal of gate 582 is input to the set terminal of RS flip-flop 604 to set it.
The output signal of the RS flip-flop 604 is applied to the gates of the transistors 602 and 603 to turn it on, and as shown in FIG. Similarly, a communication path is formed.

FIG. 7 shows a modification of FIG. 3, in which, instead of directly inputting central office line key information from a telephone into the circulating memory, it is first inputted to a processing device, etc., and after the necessary processing is performed, the CPU
This method is a method in which the output of the key telephone is inputted into the circulation memory, and this method is a practically effective means when combining other functions of the key telephone device, such as a secret call function, with the function of the present invention.

The differences between FIG. 3 and FIG. 7 are summarized below. Figure 3 shows that by providing a circulating memory corresponding to the telephone set, a memory area corresponding to the telephone line is determined, and the memory area in the circulating memory for storing central office line telephone key information is determined by the time slot and central office line that determine the memory area of the circulating memory. This method detects the arrival of the central office line telephone key information by performing a logical product with the time slot that conveys the telephone key information, and stores it in a designated memory area of the circulating memory.

On the other hand, in Fig. 7, the telephone key information coming from the telephone is once input into the processing device, and after the necessary processing is performed, the output signal is used to store the memory that latches the information corresponding to the telephone and the office line information. Divide into the memory to be latched and store the two pieces of information. This is a method in which the memory area of the circular memory is determined by the logical product of the time slot that determines the memory area of the circular memory, and the data is stored there. Here, while FIG. 3 is constructed of wired logic, the processing device of FIG. 7 is generally stored program logic.

Next, the circular memory shown in Fig. 7 is an example in which one shift register is used for each telephone.In this case, the output of the processing device is encoded, and information corresponding to the telephone is input to the shift register in the form of a code. Decode the output and expand it into information for each phone! This makes it possible to reduce memory capacity.

The configuration and operation of the embodiment shown in FIG. 7 will be explained in detail below. In FIG. 7, 701 is a processing device, 702, 703
, 704, 705, 706 are latch memories composed of D-type flip-flops, etc.; 1707, 708, 709;
, 713 and 714 are AND gates, 710 is an inverter, 711 and 718 are OR gates, 712 is a shift register, 715 is a photo coupler, and 717 is a flip-flop like 540. Here is the difference between Figure 3 and Figure 7 1
Alternatively, in FIG. 7, between the flip-flop 540 and the AND gate 511 in FIG.
, 703, 705, 707, 708, and 718 are inserted. 2 Therefore, in Figure 7, the office line key information from the telephone is flip-flopped in the same way as in Figure 3.
It is output to flop 540. The output signal is input to a processing device 701, where it is divided into telephone corresponding information and office line telephone key information under storage program control, and flip-flops 705 and 703 are respectively set to obtain an output signal at its output terminal. That is, since the output terminals of flip-flops 703 and 705 each become high level, the shift register 5 is operated in the same manner as shown in FIG.
13 in a predetermined J memory area, and the operation is the same as that shown in FIG. 3 below. Another difference between FIG. 3 and FIG. 7 is that in FIG. 3, the contents of the shift register 513 are used as means for controlling the transistor 584.
5 In Fig. 7, the processing device has a memory such as a RAM, and compares the first time slot pulse and the next time slot pulse among the office line telephone key information repeatedly sent from the telephone, and if they are different, the processing device The output signal is applied to the flip-flop 706, and its output is applied to the base of the transistor 584 via the inverter 583, turning off its collector and emitter momentarily.

The following description is omitted since it is the same as in the case of FIG. Moreover, it is natural that this part can be made as shown in FIG. As explained in detail above, the present invention can be executed not only by the wired logic method but also by the stored program logic method, and when used in a large-scale system or a system with multiple functions, it is possible to implement the present invention using the wired logic method. This method has advantages over other methods.

Therefore, in the present invention, in order to turn on the thyristor, a method is adopted in which repeated high-speed pulses are applied to the gate of the thyristor. The thyristor is configured to hold the state, but when used as a call path switch, if a reverse current exceeding the normal call level flows between the thyristor's anode and cathode due to external noise, etc., the thyristor will turn off. .

Therefore, in the present invention, in order to turn on the thyristor again to such an extent that it does not cause a practical problem when such a phenomenon occurs, an improvement is made by applying high-speed repetitive pulses to the gate of the thyristor. Next, FIG. 7 can be applied to FIG. 2.

When a telephone 301 is called by a telephone 201, when the telephone 201 dials, it is counted by a counting circuit 1, the called destination is specified based on the result, and the communication path switch corresponding to the called telephone is turned ON. Therefore, this is possible by using the processing device 701 and shift register 712 shown in FIG. 7 in place of the counting circuit 1 and flip-flop 56 shown in FIG.

That is, when a dial is made in the telephone call circuit 529 in FIG. 7, the dial impulse is input to the processing unit 701 via the photocoupler 715, processed there, and stored in the memory area designated by the shift register 712 in the same manner as described above. and its output signal is passed through the AND gate 71
4 to the gate of a call path switch of the called telephone, such as the analog switch 55 in FIG. 2, turning it ON. Thereafter, hands-free communication is enabled by the same operation as in FIG. 2 described above. This method is practically advantageous in large systems compared to the case of FIG.
．． Although the present invention has been described using a shift register as an embodiment thereof, the same effect can be obtained by using other memory means such as random access memory (RAM) and using program control by a processor or the like. can. As described above, the present invention selectively connects a plurality of button telephones each having a function of sending a dial signal to a plurality of office lines using a main device, a plurality of call lines, and a plurality of control lines. In the button telephone device, each of the plurality of button telephones includes a receiving circuit 61, 63 including a speaker, a transmitting circuit 62, 64 including a microphone, and a hybrid circuit 65 that accommodates the receiving circuit and the transmitting circuit. and a hook switch contact 60 for connecting a corresponding one 72 of the plurality of telephone lines to the hybrid circuit or the telephone circuit 58 of the telephone, the main device being connected to the plurality of button telephones. a plurality of switch means 54, 55 having a plurality of self-holding functions correspondingly inserted into each of said communication lines;
56,544-1,544-2,602,603,60
1,604, and the dialing signal for selecting the called telephone line transmitted from one calling telephone of the plurality of button telephones via the telephone line is detected by the counting means 51,1,2. selection means 52, 53, 507 for performing a selection operation for closing one of the plurality of switch means corresponding to the called telephone set and putting it in a self-holding state;
508, 509, 510, 511, 512, 513, 5
14,515, and release means 66, 73, 74, 581 for releasing the self-holding state of the plurality of switch means.
, 582, 583, 584, in the called telephone set corresponding to the self-held one of the plurality of switch means, the corresponding one communication line 72 is connected through the contact 60 of the switch when off-hook. is connected to the telephone circuit 58 to enable telephone calls using the handset of the telephone, and when on-hook, during the self-holding state, the corresponding one telephone line 72 is connected to the hybrid circuit via the contact 60 of the telephone switch. This is a hands-free calling method in a button telephone device, which is configured so that it can be connected to a 65 and can make hands-free calls.

Furthermore, power on/off means 66, 73, 74, 75, and 76 may be provided for connecting power to the receiving circuit and the transmitting circuit only in the self-holding state. As shown in FIG. 3, the self-holding state is normally configured so that the releasing means is configured to be released by control from the called telephone; in the case of FIG. The release means is configured to perform a release operation in response to lifting up of the handset of the called telephone. Further, in the case of FIG. 3, the above-mentioned release means is configured to perform the release operation in response to control of a control button provided on the called telephone set. However, the release switch 66 of FIG. 2 may be provided in the calling telephone 201 so that the releasing means releases the self-holding state in response to the calling telephone hanging up the handset. You can also use Figure 3 or Figure 6.
The release means shown in the figure may be configured to operate after a predetermined period of time after the switch means is activated, and may be configured to automatically perform the release operation when the self-holding state continues for a predetermined time. . As explained above, according to the present invention, in a hands-free call system in a key telephone device, it is possible to shorten the acquisition time of a relatively expensive dial counting circuit, improve its utilization efficiency, and achieve a substantial cost reduction. The practical effect is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a conventional hands-free call system, FIG. 2 is a block diagram showing an embodiment of the present invention, and FIG.
7 and 7 are circuit diagrams showing a specific example of communication path control in FIG. 2, FIG. 4 is a time chart for explaining the operation of the example in FIG. 3, and FIGS. 5 and 6 are FIG. 4 is a circuit diagram showing a partial modification of the specific example shown in FIG. 3;

Claims (1)

[Scope of Claims] 1. A button that selectively connects a plurality of button telephones each having a function of sending a dial signal to a plurality of office lines using a main device, a plurality of call lines, and a plurality of control lines. In the telephone device, each of the plurality of button telephones includes a receiving circuit including a speaker, a transmitting circuit including a microphone, a hybrid circuit accommodating the receiving circuit and the transmitting circuit, and one of the plurality of telephone lines. a hook switch contact for connecting the corresponding one of the above to the hybrid circuit or the telephone circuit of the telephone;
The main device includes a plurality of switch means having a plurality of self-holding functions inserted into each of the communication lines corresponding to the plurality of button telephones, and a plurality of switch means having a plurality of self-holding functions inserted into the respective communication lines corresponding to the plurality of button telephones, and a plurality of switch means having a plurality of self-holding functions inserted into the communication lines corresponding to the plurality of button telephones, and connecting the communication line from one calling telephone of the plurality of button telephones. a selection operation for detecting the dial signal for selecting the called telephone set transmitted through the switch means and closing one of the plurality of switch means corresponding to the called telephone set to a self-holding state; and a release means for releasing the self-holding state of the plurality of switch means, when the called telephone corresponding to the self-holding one of the plurality of switch means goes off-hook. A corresponding one of the plurality of communication lines is connected to the telephone circuit through a contact point of the hook switch so that a telephone call can be made using the handset of the telephone, and when on-hook, the period of the self-holding state is the same as that of the telephone circuit. 1. A hand-held telephone call system in a button telephone device, characterized in that one telephone line connected to the hybrid circuit via a contact point of the hook switch allows hands-free telephone communication. 2. A hands-free telephone call system in a button telephone device according to claim 1, wherein the releasing means is configured such that the self-holding state is released by control from the called telephone. 3. A hands-free telephone call system in a button telephone device according to claim 2, wherein said release means is configured to perform a release operation in response to lifting of the handset of said called telephone. 4. The hand button telephone device according to claim 2, wherein the release means is configured to perform a release operation in response to control of a control button provided on the called telephone. Free calling method. 5. The button telephone device according to claim 1, wherein the releasing means is configured to release the self-holding state in response to the calling telephone setting down the handset. Hands-free calling method. 6. The hand in the button telephone device according to claim 1, wherein the release means is configured to automatically perform a release operation when the self-holding state continues for a predetermined period of time. Free calling method. 7. In a button telephone device in which a plurality of key telephones, each having a function of transmitting a dial signal, are selectively connected to a plurality of office lines using a main device, a plurality of call lines, and a plurality of control lines, the plurality of Each of the button telephones includes a receiving circuit including a speaker, a transmitting circuit including a microphone, a hybrid circuit accommodating the receiving circuit and the transmitting circuit, and a corresponding one of the plurality of telephone lines. and a hook switch contact for connecting the telephone to the hybrid circuit or the telephone circuit of the telephone, and the main device has a plurality of self-holding functions inserted into each of the telephone lines corresponding to the plurality of button telephones. a plurality of switch means having a plurality of switch means, and one of the plurality of switch means for detecting the dial signal for selecting a called telephone set transmitted from one calling telephone of the plurality of button telephones via the telephone line; selection means for performing a selection operation to close one corresponding to the called telephone set to put it into a self-holding state; a canceling means for releasing the self-holding state of the plurality of switch means; and a releasing means for canceling the self-holding state of the plurality of switch means, power on/off means for connecting power to the receiving circuit and the transmitting circuit only when the called telephone set corresponding to the self-maintained one of the plurality of switch means is off-hook; The corresponding one telephone line is connected to the telephone circuit through the contact point of the hook switch, and a telephone call can be made using the handset of the telephone, and when on-hook, the corresponding one telephone call is connected during the self-holding state. A hands-free calling system in a key telephone device, characterized in that a line is connected to the hybrid circuit via a contact point of the hook switch so that hands-free calling is possible. 8. A hands-free telephone call system in a button telephone device according to claim 7, wherein the releasing means is configured so that the self-holding state is released by control from the called telephone. 9. A hands-free telephone call system in a pushbutton telephone device according to claim 8, characterized in that said release means is configured to perform a release operation in response to lifting of the handset of said called telephone. 10. The hand button telephone device according to claim 8, wherein the release means is configured to perform a release operation in response to control of a control button provided on the called telephone. Free calling method. 11. The button telephone device according to claim 7, wherein the release means is configured to release the self-holding state in response to the calling telephone setting down the handset. Hands-free calling method. 12. The hand in the button telephone device according to claim 7, wherein the releasing means is configured to automatically perform a releasing operation when the self-holding state continues for a predetermined period of time. Free calling method.