JPH01288145A - Howling prevention system at loudspeaker talking end - Google Patents

Abstract

PURPOSE:To prevent howling caused transiently at the end of call by applying direct howling preventing control to a talking control section of a loudspeaking telephone set when a talking current from the loudspeaking telephone set to an opposite telephone set is not given. CONSTITUTION:While each section of a doorphone talking control section 13 is in operation from the on-hook at an extension telephone set 21 till the end of talking processing, the state of disconnecting the extension telephone set 21 from a hybrid circuit 132 is caused transiently, but the interruption of the supply of speech current is detected immediately by a howling prevention circuit 15, the input of a transmission amplifier 134 is connected to ground in terms of AC to block the forming of a positive feedback path, then no howling is caused even in the moment of on-hook of the extension telephone set 21.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a howling prevention method for a telephone device to which a loudspeaker telephone is connected, and in particular, to prevent howling that occurs transiently in a loudspeaker telephone at the end of a loudspeaker call. This is related to the method of doing so. (Background of the invention and prior art) For example, a telephone device in which a so-called doorphone installed at an entrance etc. is connected to an extension side is known.In such telephone devices, the doorphone is often not equipped with a handset and has no function Specifically, it is a loudspeaker telephone (vans-free telephone).Furthermore, in a telephone device such as a key telephone system, an extension telephone is often equipped with a function that can be used as a loudspeaker telephone.

In a loudspeaker call using such a loudspeaker telephone, the other party's telephone is connected to the telephone circuit (hybrid circuit for 2-wire to 4-wire conversion) of the loudspeaker telephone during the call. However, when ending a call, if the telephone at the other end of the call on the loudspeaker telephone ends the call (on-footer) before the loudspeaker telephone does (especially with a doorbell, the call end operation may not be possible). (Since the telephone on the other end of the call always ends the call first.), until the call termination process for the loudspeaker telephone is completed, the circuit of the loudspeaker telephone becomes unbalanced, resulting in howling. .

In order to prevent this howling at the end of a call, conventionally the central processing unit within the telephone device performs the following control. That is, when the central processing unit detects that the other party's telephone has terminated the call, it connects the howling prevention means to the telephone circuit of the loudspeaker telephone and maintains the balance of the circuit until the end of the call is performed on the loudspeaker telephone. or
Alternatively, howling at the end of a call is prevented by connecting the call circuit to an equivalent pseudo load.

(Problem to be Solved by the Invention) It takes a long time for the central processing unit to perform the control to connect the howling prevention means to the communication circuit of the loudspeaker telephone after the central processing unit detects the on-footer of the other party's telephone. Since a time difference occurs based on the processing time, it is unavoidable that the communication circuit of the loudspeaker telephone becomes unbalanced during that time using the conventional method of connecting howling prevention means using a central processing unit, and howling will occur instantaneously. . In particular, in the case of a loudspeaker telephone or a so-called doorphone, a short ringing sound due to howling is always generated before the central processing unit completes the call termination process for the doorphone, as the call termination operation is not performed on the doorphone itself.

The present invention is proposed to solve the above problems.
The object of the present invention is to provide a method for preventing howling that can even prevent howling that occurs transiently at the end of a call.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention monitors the calling current of the loudspeaker telephone to the other party's telephone, and when the talking current stops flowing, the loudspeaker telephone Howling prevention control is performed directly on the call control unit (without being controlled by the central processing unit).

(Function) Until the on-footer of the other party's phone is detected on the loudspeaker telephone and the central processing unit finishes the call termination process for the loudspeaker telephone, the central processing unit Howling prevention control is performed through a route separate from the on-footer detection and call termination processing route, thereby eliminating transient howling when a call is terminated.

(Embodiment) The drawing is a block diagram partially showing a main part of an embodiment of the present invention as a circuit diagram. In addition, A in the drawing.

The locations indicated by B and C indicate that the same symbols are connected to each other. Moreover, this embodiment is an embodiment in which the loudspeaker telephone is a doorbell.

As shown in the drawings, a system implementing the present invention is constructed of a main device 1, two extension telephones 21 and 22, and one door phone 3, for example.

The main device 1 includes a connection control unit 11 that performs connection control for external lines or inter-extension communication between extension telephones 21 and 22, a communication current supply unit 12 that supplies communication current for inter-extension communication and relays the voice of the intercom call, A door phone call control unit 13 that controls a door phone call, a startup circuit 14 that controls the startup of a door phone call, a howling prevention circuit 15 that performs howling prevention control including transient howling at the end of a call, and control of the main device 1. It is composed of a central processing unit 16 and the like that performs all of the above in one go.

The connection control unit 11 includes contacts 11.22 for switching and controlling the extension telephones 21.22 to an outside line or an extension-to-extension call. Consisting of loop monitoring means PCI and PC2 for monitoring calls between JIL2 and extension telephones 21 and 22, the contact points 11.
R,2 are contacts of relays Ll, L2 whose operation is controlled by the central processing unit 16, and loop monitoring means Pct, PC2
are each composed of a photocoupler, for example.

The call current supply unit 12 is composed of a DC power supply E1 which is a call current supply source, a transformer T1 which also serves as a blocking wire for supplying a call current, and a resistor R1, R2 for relaying the voice of a doorphone call.

The door phone call control unit 13 includes a switch circuit 131 for door phone calls, two hybrid circuits 132 and 133 for 2-wire to 4-wire exchange, and amplifies the outgoing voice or the received voice, respectively, as seen from the door phone 3 side. It is composed of a transmitting amplifier 134, a receiving amplifier 135, and the like.

The starting circuit 14 is constituted by a switch using a transistor, for example, and connects the DC power supply E2 to the transmitting amplifier 134 and the receiving amplifier 135 of the door intercom call control section 13 during a door intercom call.

The howling prevention circuit 15 is configured with a switch using a transistor, for example, and when the call current stops flowing in the call current supply section 12, the howling prevention circuit 15 is configured to switch the intercom call control section 13.
The input of the transmitting amplifier 134 is grounded in an alternating current manner, and the audio signal input to the transmitting amplifier 134 is cut off.

The central processing unit 16 is mainly composed of a so-called one-chip CPU, and controls the main device 1 at once according to a program input in advance.

For example, the operation of this embodiment will be explained using a case where the extension telephone 21 is talking to the doorbell 3 as an example.

When the extension telephone 21 and the doorbell 3 are talking, the central processing unit 16 operates the relay L1, and therefore the contact 11 in the connection control unit 11 switches in the opposite direction to that shown in the figure, and the extension telephone 21 There is a communication current supply section 1
A communication current is supplied from the DC power supply E1 of No. 2 through the following path (1).

El-R2-T-β1-PCI-21-ul-T-R1
- Earth...path (1) The call current flowing in the above path (1) is detected by the loop monitoring means PCI, and the central processing unit 16 detects that the extension telephone 21 is busy in a call based on the detection signal of the loop monitoring means PCI. I am aware of this.

Further, the central processing unit 16 conducts the switch circuit 131 of the door intercom call control unit 13 to form an audio transmission path between the transformer T of the call current supply unit 1 2 and the hybrid circuit 132 of the intercom call control unit 13 . It also controls the starting circuit 14 to activate the transmitting amplifier 1 of the door intercom call control section 13.
34 and the receiving amplifier 135 from the power supply E2, and the howling prevention circuit 15 is connected to the above path (1
), the voltage between both ends of the resistor R1 is inputted, and the output line a is in a non-operating state (the output line a is not grounded in an alternating current manner).

As described above, in the door intercom call control unit 13, the switch circuit 1311, the hybrid circuit 132, the transmitting amplifier 134
, the receiving amplifier 135 and the hybrid circuit 133 are all connected in an active state, and the extension telephone 21
It is possible to make a call between the user and the doorbell 3.

When the extension telephone 21 goes on-hook, the path (1) is cut off and the extension call current stops flowing. When the loop monitoring means PCI detects this, the central processing unit 16 determines that the extension telephone 21 has finished the call, and the door intercom In other words, the switch circuit 131 is opened, and the startup circuit 14 is controlled to cut off the supply of operating power to the transmitting amplifier 134 and the receiving amplifier 135. Also,
The central processing unit 16 performs restoration control on the relay L1 to return the contact λ1 of the connection control section 11 to its original state (the state shown in the figure), thereby eliminating the extension communication path itself.

From the time the extension telephone 21 is on-hook until the above-described call termination process is completed, the extension telephone 21 is disconnected from the hybrid circuit 132 while each part of the door intercom call control section 13 is operating. occurs transiently.

At this moment, the balance of the hybrid circuit 132 collapses, and the hybrid circuit 132 causes the transmission amplifier 13 to
A positive feedback path of the audio looping around from 4 to the receiving amplifier 135 is formed, resulting in a state in which howling occurs instantaneously. However, in the present invention, the howling prevention circuit 15 immediately detects that the supply of talking current is cut off from the path (1), and the human power of the sending amplifier 134 is grounded in an alternating current manner. Since the formation is prevented, the extension telephone 21
Howling does not occur even at the moment of on-footer.

In the above embodiment, the input of the transmitter amplifier 134 is grounded in an alternating current manner to prevent howling.
Howling prevention control can be performed at any appropriate location on the positive feedback path.

(Effects of the Invention) As explained above, the present invention provides an advantage that, in a loudspeaker call such as a doorbell call, when the telephone that is in the talking state with the loudspeaker telephone is on-hook and the call current stops flowing, the call control unit is activated. This system immediately performs howling prevention control, and has the remarkable effect of preventing transient howling that occurs between the on-footer of the telephone and the completion of call termination processing for the loudspeaker telephone by the central processing unit. There is.

[Brief explanation of the drawing]

The drawing is a block diagram partially showing a main part of an embodiment of the present invention as a circuit diagram. (Main symbols) 1... Main device, 21.22... Extension telephone, 3... Door phone (public address telephone), 12... Call current supply section, 13... Door phone call control section, 15...Howling prevention circuit, 16...Central processing unit.

Claims (1)

[Claims] 1. When a telephone device to which a public address telephone is connected is on-hook with a telephone that is in communication with the public address telephone, the supply of communication current to the on-hook telephone is cut off, causing the telephone to be connected to the public address telephone. A method for preventing howling during a loudspeaker telephone call in which howling prevention control is performed directly on the call control unit.