JP2618683B2 - Intercom system - Google Patents

Description

The present invention relates to an intercom system, and more particularly, to a signal transmission method for an intercom system.

[Prior Art] FIG. 3 is an explanatory diagram showing a configuration of a conventional intercom system.

In the figure, reference numeral 100 denotes an intercom master unit, which includes a power supply circuit 101, a transmission IC 102, a transmission unit 103, a telecommunications unit 104, and a communication circuit 105, and includes a power supply voltage terminal T1, a control signal transmission terminal T2, and a communication signal transmission terminal T3. And a common ground terminal TC.

On the other hand, the intercom secondary master unit 200 includes the transmission IC 201 and the transmission unit.
It comprises a 202, a receiving unit 203, and a communication circuit 204, and has connection terminals T1 to T3 and TC as in the above-mentioned master unit.

As for the connection terminals of the base unit 100 and the small device 200, T1 is a power supply voltage supply line l1, T2 is a control signal transmission line l2,
T3 are connected to each other by a communication signal transmission line 13 and TCs are connected to each other by a common ground line IC.

The operation will be described with reference to the figure. When a call button (not shown) or an emergency button (not shown) provided on the base unit 100 is operated, a digital control signal is sent from the transmission IC to the transmission unit 103, and the transistors Q101 and Q102 Drive the control signal transmission line l2
Is transmitted to the sub-base unit 200 via.

On the side of the sub master unit 200, the control signal is blocked by the diode D201 of the transmission unit 202, so that the control signal drives the transistor Q203 through the resistor R201 of the reception unit 203, and the control signal is input to the transmission IC 201, and necessary control is performed. Done.

Conversely, the control signal from the transmission IC 201 of the sub master unit 200 drives the transistors Q201 and Q202 of the transmission unit 202, and is transmitted to the master unit 100 side via the control signal transmission line l2, and the transmission unit 103
, And the transistor Q103 is driven through the resistor R101 of the receiving unit 104 to input a control signal to the transmission IC. Then, call signals from the call circuit 105 of the base unit 100 and the call circuit 204 of the sub-base unit 200 are transmitted through a call signal transmission line 13 and a call is made by a handset (not shown) provided for each.

In the intercom system having such a configuration, the secondary master unit
The control signal current transmitted from 200 is the power circuit of master unit 100
The power supply circuit 10 is output from the transmission unit 202 of the sub master unit 200 which receives power supply from the base unit 101 via the power supply voltage supply line l1, and is transmitted through the reception unit 104 of the master unit 100 via the control signal transmission line l2.
1, while the control signal current transmitted from the base unit 100 to the sub-base unit 200 is output from the transmission unit 103 of the base unit 100 that receives power from the power supply circuit 101 of the base unit 100, The signal flows through the receiving unit 203 of the sub master unit 200 via the signal transmission line l2, and returns to the power supply circuit 101 via the common ground line IC as indicated by a broken line.

That is, when a control signal is transmitted from master device 100 to sub-master device 200, a control signal current flows through common ground line IC.

When the distance between the master unit 100 and the sub master unit 200 is small, there is no problem because the resistance component of the common ground line IC is small, but as the distance increases, the resistance component of the common ground line IC increases, and this resistance increases. Since the control signal current flows through the components, the potential of the common ground terminal TC of the sub-base unit 200 changes according to the control signal current, and the ground potential of the communication circuit 204 of the sub-base unit 200 also changes at the same time. This fluctuating potential is superimposed on the call signal, causing interference.

As a countermeasure against such a call signal, the distance between the master unit 100 and the sub master unit 200 is limited to reduce the resistance component of the common ground line IC to a certain value or less, and the potential fluctuation of the common ground terminal TC of the sub master unit 200 is reduced. Or reduce the receiving unit 2 of the secondary master unit 200.
By increasing the value of the resistor R201 of 03, a method of reducing the control signal current to reduce the potential fluctuation of the common ground terminal TC is adopted, but when the length of the common ground line IC is limited, If the distance between the master unit 100 and the auxiliary master unit 200 increases, there is a problem that facilities cannot be provided.

In general, if the line impedance of a signal transmission line rises, noise from the surroundings, for example, so-called hum noise from a commercial power supply voltage, or radio noise from a broadcasting station, amateur radio, or the like, is easily induced on the transmission line and controlled. Signals are more susceptible to interference.

By the way, if the value of the input resistor R203 of the receiving unit 203 is increased to prevent the potential fluctuation of the common ground terminal TC of the sub-base unit 200, the fluctuation of the potential of the common ground terminal TC of the sub-base unit 200 is suppressed. The design is difficult due to the inconvenient inconvenience that external noise is likely to be induced on the control signal transmission line.

Further, even when the potential fluctuation of the common ground terminal TC and the induction noise of the control signal transmission line l2 are adjusted in a state where only one sub master unit 200 is connected, the sub master unit 200 is normally connected. Since a plurality of terminals T1 to T3 and a plurality of TCs are connected through a connection, the receiving units 203 of the plurality of sub master units 200 are connected in parallel to the control signal transmission line l2,
The impedance of the transmission line decreases, which is advantageous for induction of external noise.However, on the contrary, the control signal current flowing through the common ground line IC increases, and the fluctuation of the potential of the common ground terminal TC increases. Difficult.

[Problem to be Solved by the Invention] The first invention proposed to solve the above problem suppresses the induction of external noise of a transmission line in a control signal, and at the same time, causes a potential fluctuation due to a current flowing through a common ground line. In addition, the second invention of the present invention, which is proposed at the same time, does not depend on the level fluctuation of the control signal transmitted on the control signal line.
It is an object of the present invention to provide an intercom system in which a current flowing through the common ground line is kept constant to prevent potential fluctuations and suppress induction of external noise.

[Means for Solving the Problems] According to a first aspect of the present invention, which is proposed to achieve the above object, an interphone master unit and an interphone sub master unit have
A power supply voltage supply line, a control signal transmission line, and a call signal transmission line are connected by a common ground line, and the interphone sub-base unit is improved by an interphone system in which power is supplied from the interphone base unit through a power supply line. The control signal transmission line is grounded by low resistance on the side of the intercom master unit, and the input resistance value of the receiving unit of the sub master unit is increased.

Also, a second feature of the present invention proposed at the same time is that the intercom secondary master unit has a first transistor driven when a control signal transmitted through a control signal transmission line is at “H” level, A current adjusting circuit combining a second transistor driven when the transmitted control signal is at the "L"level; and providing the same current value when driving each of the first transistor and the second transistor. It is characterized by having.

[Operation] In the interphone system according to the first aspect of the present invention, the line impedance of the control signal transmission line is reduced by grounding the control signal transmission line on the side of the intercom master unit through a low resistance. In addition to preventing induction to the line, the current flowing through the common ground line is reduced by increasing the input resistance of the receiver even when multiple sub master units are connected, and the potential fluctuation due to the resistance component of the common ground line is reduced. Can be reduced.

Further, in the second aspect of the present invention, the current flowing from the receiving section of the sub master unit to the common ground terminal is always kept constant in accordance with the level fluctuation of the control signal transmitted through the control signal transmission line, so that the common ground line Eliminating potential fluctuation due to the resistance component and further reducing the input resistance value of the receiving section can prevent external noise induced in the control signal transmission line.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing a main part of the first present invention. In the figure, A is an intercom master unit, and a power supply circuit 1,
It comprises a transmission required IC 2, a transmission unit 3, a reception unit 4, and a communication circuit 5, and has a power supply voltage terminal T1, a control signal transmission terminal T2, a communication signal transmission terminal T3, and a common ground terminal TC.

On the other hand, the interphone sub-base unit B includes a transmission IC 6, a transmission unit 7, a reception unit 8, and a communication circuit 9, and has connection terminals T1 to T3 and TC, similarly to the base unit.

In the connection terminals of the master unit A and the sub master unit B, T1 is a power voltage supply line l1 and T2 is a control signal transmission line l2.
T3 are connected to each other by a communication signal transmission line l3, and TCs are connected to each other by a common ground line lC.

The operation will be described with reference to the figure. When a call button (not shown) or an emergency button (not shown) provided on the base unit A is operated, a digital control signal is sent from the transmission IC 2 to the transmission unit 3, and the transistors Q1, Q2 And is transmitted to the sub-base unit B via the control signal transmission line l2.

On the side of the sub master unit B, the control signal is blocked by the diode D2 of the transmission unit 7, so that the control signal drives the transistor Q6 through the resistor R2 of the reception unit 8, and the control signal is input to the transmission IC 6, and the necessary control is performed. Done.

Conversely, the control signal of the transmission IC 6 of the sub master unit B is
Drive the transistors Q3 and Q4 of the control signal transmission line l
2 to the master unit A side, and the diode D of the transmission unit 3
1 and the transistor Q through the resistor R1 of the receiver 4.
5 is driven to input a control signal to the transmission IC 2.

The communication signals from the communication circuit 5 of the master unit A and the communication circuit 9 of the sub master unit B are transmitted through a communication signal transmission line 13 and a call is made by a handset (not shown) provided for each.

Further, in this embodiment, a low resistance RO is provided between the control signal transmission terminal T2 of the master unit A and the common ground terminal TC, and the resistance R2 of the receiving unit 8 of the sub master unit B is set to a high resistance. .

Therefore, the control signal current transmitted from master unit A to sub master unit B depends on master unit A that has received power from power supply circuit 1 of master unit A.
The current I is output from the transmission unit 3 of the sub master B via the control signal transmission line l2, and returns to the power supply circuit 101 via the common ground line IC as shown by the broken line as shown by the broken line.
Although 0 flows, the value is small because the value of the resistance R2 of the sub master unit B is large. Accordingly, even when several sub-base units B are connected, the sub-base unit B
The fluctuation of the potential of the common ground terminal TC on the side is very small, and the disturbance to the call signal can be greatly reduced.

In addition, since a low resistance RO is provided at the control signal input / output terminal T2 on the master unit A side, the line impedance of the control signal transmission line l2 can be reduced, and it is difficult to receive external noise such as a commercial power supply or a radio wave. .

Next, FIG. 3 is a main part circuit diagram for explaining the second embodiment of the present invention, and the same portions as those in the first embodiment are denoted by the same reference numerals and the description thereof will be omitted. The difference from the first invention is that the low resistance of the control signal transmission terminal T2 of the master unit A is eliminated, and that the current adjustment circuit 10 is provided in the receiving unit of the sub master unit B.

The control signal current from the master unit A is the control signal transmission line l2
Is input to the current adjustment circuit 10 of the sub-base unit B via. This circuit is configured by connecting two transistors Q7 and Q2R as shown in the figure. In this circuit 10, when the control signal is at the "H" level, the base current flows to the first transistor Q7 through the resistor R3 and turns on. Therefore, the collector current of the first transistor Q7 flows from the power supply voltage through the resistor R4, As indicated by the broken line, the sum of the base current and the collector current I1 returns from the emitter of the first transistor Q7 to the master A via the common ground line IC.

On the other hand, when the control signal is at the "L" level, the first transistor Q7 is turned off, so that the base current flows from the power supply voltage to the second transistor Q8 through the resistor R4 and turns on. A current flows, and the sum I2 of the base current and the collector current flows from the emitter of the second transistor Q8 to the common ground line IC as shown by the broken line.
Flows into the parent machine A side through.

Therefore, by appropriately selecting the values of the resistors R3 to R5 of the receiving unit 10 (if the "H" level of the control signal voltage is substantially the same as the power supply voltage, all the resistors R3 to R5 have the same value). When the control signal is at the "H" level and when the control signal is at the "L" level, the currents I1 and I2 flowing through the common ground line IC are equalized, so that the current flowing through the common ground line IC is always constant. In other words, although a potential difference is generated between the common ground terminals of the master unit A and the sub master unit B due to the resistance component of the common ground line IC, no potential fluctuation occurs, so that it is possible to prevent interference with the call signal.

In addition, in the current adjusting circuit 10, even if the resistors R3 to R5 are set to low resistance, the currents I1 and I2 increase but the potential does not fluctuate in the common ground line IC. Accordingly, it is possible to lower the line impedance of the control signal transmission line l2 and prevent the influence of external noise.

[Effects of the Invention] According to the first aspect of the present invention, it is possible to reduce disturbance of external noise in a control signal transmission line with a simple configuration, reduce current flowing in a common ground line, and remove disturbance to a speech signal. Further, in the second aspect of the present invention, the current flowing through the common ground line according to the voltage fluctuation of the control signal transmitted on the control signal transmission line is made constant by the current adjusting circuit, thereby changing the ground potential. And the induction of extraneous noise can be suppressed.

[Brief description of the drawings]

FIG. 1 is a block diagram of a main part of a first embodiment of the present invention, FIG. 2 is a block diagram of a main part of a second embodiment of the present invention, and FIG. [Description of Signs] A: Interphone master unit B: Interphone sub master unit l1: Power supply voltage supply line l2: Control signal transmission line l3: Call signal transmission line lC: Common ground line TC: Common ground Terminal 3 Transmitter (Master A) 7 Transmitter (Sub-Master B) 4 Receiver (Master A) 8 Receiver (Sub-Master B) 10 Current adjustment circuit Q7 …… First transistor Q8 …… Second transistor

Claims (2)

(57) [Claims] An interphone master and an interphone sub-master are connected by a power voltage supply line, a control signal transmission line, a call signal transmission line and a common ground line, and the interphone sub-master is connected to the interphone master. In the intercom system in which power is supplied through a power supply voltage supply line, the control signal transmission line is grounded by low resistance on the interphone master unit side, and an input resistance value of a receiving unit of the sub master unit is increased. An intercom system characterized in that: 2. An interphone master unit and an interphone sub master unit are connected by a power voltage supply line, a control signal transmission line, a communication signal transmission line and a common ground line, and the interphone sub master unit is connected to the interphone master unit by the interphone master unit. In an intercom system configured to be supplied with power through a power supply voltage line, the interphone sub-base unit includes a first transistor driven when a control signal transmitted through a control signal transmission line is at “H” level; A current adjusting circuit combining a second transistor driven when the control signal transmitted through the transmission line is at the "L"level; and a current flowing value when each of the first transistor and the second transistor is driven. An intercom system characterized by having almost the same.