JPH0728344B2 - Door phone circuit - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a doorphone circuit in a button telephone device or the like.

[Technical Background of the Invention] Generally, in such an intercom circuit, as shown in FIG. 2, when the calling switch 11 of the intercom slave 10 is first pressed, the line 12 and the resistor 13 are supplied from the power source of the current detection circuit 14. Current flows through. When the current detection circuit 14 detects this current, the current detection circuit 14 outputs a detection signal, and the control signal 15 causes the control device 15 to perform a control operation so that the telephone 16 produces a ringing tone.

And when the operator picks up the handset of telephone 16, the telephone
The hook switch (not shown) 16 is closed to enter the off-hook state, and the relay switch 17 is activated by the signal generated at this time.
The contact of closes. When the relay switch 17 is closed, power is supplied from the constant current source 18 to the microphone amplifier 19 of the intercom slave 10 and the operator picks up the handset on the main unit 20 side and presses the call switch 11 on the intercom slave 10 side. A call can be communicated with a visitor via a call path switch 21, side-tone prevention circuits 22 to 24 for preventing side sounds, a microphone 25, and a speaker 26.

Further, the amplifiers 27 and 28 are connected to the main device 20 side to form a 4-wire type circuit, and compensate for line loss.

[Problems with the background art] However, in such a device, since the amplifier is included in the main device to perform two-way communication, the circuit configuration of the main device is converted into 2 lines-4 lines-2 lines. In addition, since the side soundproof circuit is also included in the intercom slave unit, the side sound may worsen when the line length changes, and the volume of the speaker or microphone may not be sufficient. there were.

[Object of the Invention] The present invention has been made in view of the above problems, and an object of the present invention is to provide an intercom circuit in which the volume of a call can be sufficiently taken.

[Summary of the Invention] In order to achieve the above object, according to the present invention, an intercom slave unit and a main device are connected by a pair of lines, and the intercom slave unit for calling is connected between the pair of lines. A switch, and a microphone and a speaker connected to the pair of lines via a sound-proof sound circuit, the main device,
A current detection circuit that detects an ON operation of the calling switch by applying a detection current to the pair of lines, a telephone that generates a ringing tone based on the detection output of the current detection circuit, and an off-hook operation of the telephone. In a doorphone circuit including a relay switch and a power supply that supplies a circuit current larger than the detected current to the doorphone slave unit via the pair of lines when the relay switch operates, the doorphone slave unit includes: A speaker amplifier for amplifying an audio signal applied to the speaker, a voltage detection circuit for detecting a voltage between the pair of lines, and a switch unit which is turned on by a detection output of the voltage detection circuit provided on the line. However, the switch means prevents the malfunction caused by the detection current flowing through the speaker amplifier. It is characterized in.

Embodiments of the Invention Embodiments of the present invention will be described in detail with reference to the drawing of FIG.

In FIG. 1, components having the same functions as those in FIG. 2 are designated by the same reference numerals for convenience of explanation. The calling operation is similar to that of the conventional example shown in FIG.

The intercom circuit of the present invention differs from that of FIG. 2 in that the circuit speaker amplifier 30 on the intercom slave unit 10 side is connected. However, if the speaker amplifier 30 is simply connected to the intercom slave 10, the current flows through the speaker amplifier 30 even when the calling switch 11 is in the open state, and the current detection circuit 14 detects this current. . Then, as in FIG. 2, the control device 15 controls the telephone 16 to generate a ringing tone. Therefore, the voltage detection circuit 31 for detecting the power supply voltage and the voltage detection circuit are further detected in the circuit of the intercom slave 10 side.
The switch 32 operated by the output of 31 was connected. Then, the threshold value of the detection voltage of the voltage detection circuit 31 is set higher than the power supply for current detection of the current detection circuit 14, and the switch 32 is activated by the power supply for current detection of the current detection circuit 14 to cause the speaker amplifier 30 to operate. Prevents malfunction of current flow.

Here, for example, the detection power supply of the current detection circuit 14 is set to about 3V, the threshold voltage of the voltage detection circuit 31 is set to about 4V,
When the operator picks up the handset of the telephone 16 in response to a call from the intercom slave 10, the contact of the relay switch 17 is closed by the signal generated at that time. The voltage across the line 12 becomes about 8V by the constant current source 18. Therefore, the voltage detection circuit 31 detects this voltage and operates,
32 is activated by the output of the voltage detection circuit 31 and is closed. Therefore, power is supplied from the constant current source 18 to the microphone amplifier 19 and the speaker amplifier 30 of the intercom slave 10, and
A call can be made between the intercom slave 10 having a line circuit and the main device 20 having a circuit configuration of only two lines.

The voice input from the microphone 25 during a call is prevented from sidetone to the speaker 26 by the protection side sound circuit 24 and is directly output to the telephone set 16 on the main unit 20 side via the line 12. No sidetone circuitry and amplifier required. Therefore, the restriction on the gain in the main device is reduced, and the volume of the call can be increased accordingly.

[Effects of the Invention] As described above, according to the present invention, the intercom slave has a speaker amplifier, a voltage detection circuit for detecting a power supply voltage, and
Since a switch element that operates by the output of the voltage detection circuit is provided and power is supplied to the speaker amplifier when the telephone is off-hook, there is an effect that the volume of a call can be sufficiently taken.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a conventional block diagram. 10 …… doorphone handset, 11 …… call switch, 16 ……
Telephone, 18 ... Constant current source, 20 ... Main unit, 25 ... Microphone, 26 ... Speaker, 30 ... Speaker amplifier, 31 ...
… Voltage detection circuit, 32… Switch.

Claims (1)

[Claims] 1. A doorphone handset and a main device are connected by a pair of lines, and the doorphone handset is provided with a calling switch connected between the pair of lines and a soundproof sound circuit on the pair of lines. A microphone and a speaker connected through the main device, and the main device detects a turn-on operation of the calling switch by applying a detection current to the pair of lines, and a detection of the current detection circuit. A telephone that generates a ringing tone based on the output, a relay switch that operates by an off-hook of the telephone, and a circuit current that is larger than the detected current to the intercom slave when the relay switch operates through the pair of lines. An intercom circuit including a power source for supplying the intercom slave, the intercom slave device includes a speaker amplifier that amplifies a sound signal applied to the speaker. A voltage detection circuit that detects a voltage between the pair of lines, and a switch unit that is provided on the line and that is turned on by a detection output of the voltage detection circuit are provided, and the detection current is supplied to the speaker amplifier by the switch unit. An intercom circuit characterized by preventing malfunction due to flowing.