JPH02117221A - Bidirectional signal transmission circuit - Google Patents

Abstract

PURPOSE:To reduce a cost by setting only one system of signal transmission circuit by detecting change at devices set oppositely by changing the voltage of a signal line by a first device and impedance by a second device, and transmitting a signal mutually. CONSTITUTION:A voltage switching means 15 consisting of a switching device 13 and a voltage source 14 is provided in a tuner 2. An impedance switching means 20 consisting of a resistance element 17, a switching device 18, and a bypass 19 is provided on the CD player 3 side of the signal line 11. A comparator 21 which functions as an impedance detecting means is provided between the line 11 and the resistance element 12, and a signal Lo when the voltage of the line 11 exceeds a threshold value and a signal Hi when it is less than the threshold value are outputted. A comparator 25 which functions as a voltage detecting means is provided between the line 11 and a resistance element 16, and the signal Hi when the voltage of the line 11 exceeds the threshold value and the signal Lo when it is less than that are outputted. Since the output of the comparators 21 and 25 are switched to Hi or Lo based on the disconnection of the switching devices 13 and 18, it is possible to transmit the signal in two ways by providing only one system of signal line 11.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a circuit that transmits signals in both directions, and the present invention relates to a circuit that transmits signals bidirectionally between devices in a system composed of a plurality of devices, such as a home or automobile audio system. It can be used for signal transmission, etc.

[Conventional technology]

Traditionally, audio systems such as car audio, etc.
In systems that selectively operate multiple devices,
When any device is selected, it is necessary to coordinate operations within the system so that other devices do not operate at the same time. In order to perform such operation coordination, in conventional systems, a signal transmission circuit is provided between each device to mutually transmit the selection state of each device.

For example, the audio system 30 shown in FIG. 3 includes a tuner 31, a CD player 32, and a deck amplifier 33, and each device is configured to be selected and operated by an external operation.

Here, between the tuner 31 and the CD player 32,
A signal transmission circuit 34 is provided to transmit signals from the tuner 31 to the CD player 32.

This signal transmission circuit 34 has a signal line 35 connecting the tuner 31 and the CD player 32, and the signal line 35 is connected to the tuner 31 side of the signal line 35 when the tuner 31 is selected.
A voltage source 36 and a switch element 37 are provided to apply a predetermined voltage to 5.

Further, a voltage source 3 is connected to the CD player 32 side of the signal line 35.
A voltage detection means 38 for detecting the voltage applied from the CD player 38 is provided, and the CD player 32 is configured to stop its operation when the detection means detects the voltage on the third day.

Therefore, when the tuner 31 is selected while the CD player 32 is operating, the operation of the CD player 32 is stopped in response to the signal transmission by the signal transmission circuit 34, and both do not operate at the same time.

The signal transmission by the signal transmission circuit 34 is limited to one direction from the tuner 31 to the CD player 32. For this reason, a signal transmission circuit 34 is a circuit similar to the signal transmission circuit 34, but the tuner 31 side and the CD player 32 side are switched.
A is provided so that signals can also be transmitted in the opposite direction from the CD player 32 to the tuner 31, and signals are transmitted in both directions by these two signal transmission circuits 34 and 34A.

Note that the CD player 32 is connected to a deck amplifier 33, and similar signal transmission circuits 34B and 34C are provided between the CD player 32 and the deck amplifier 33.

Here, in the CD player 32, the signal transmission circuit 3
The voltage detection means 38 of No. 4 is linked to the switch element 37B of the signal transfer circuit 34B, and the voltage detection means 38C of the signal transfer circuit 34C is linked to the switch element 37B of the signal transfer circuit 34A.
7A, and the tuner 3 is connected to the CD player 32.
1. When a signal is transmitted by voltage from any device of the deck amplifier 33, it is configured so that the signal can also be transmitted to other devices.

Therefore, if another device is selected while one of the devices is in operation, that device becomes in the operating state and the signal transmission circuit 3
4. Signals are transmitted to other devices via 34A, 34B, and 34C, and devices that were already in operation are stopped from operating.
Only one device within system 30 will be selected.

[Problem to be solved by the invention]

However, in such a conventional system 30, two signal transmission circuits are arranged between each device, which increases the cost of the entire system 30 and requires two signal lines between each device. This poses a problem in that the connections become complicated and the handling becomes difficult.

SUMMARY OF THE INVENTION An object of the present invention is to provide a bidirectional signal transmission circuit that can be connected easily and at low cost.

[Means to solve the problem]

The present invention is a signal transmission circuit that bidirectionally transmits signals by a single signal line connecting a first and a second device,
The first device is provided with a voltage switching means for changing the voltage applied to the signal line according to the output of the device, and the second device is provided with a voltage switching means for detecting the voltage change of the signal line by the voltage switching means. A voltage detecting means for receiving the output of the first device is provided, a second device is provided with an impedance switching device for changing the impedance of the signal line according to the output of this device, and the first device is provided with a voltage detecting means for receiving the output of the first device. The bidirectional signal transmission circuit includes impedance detection means for detecting an impedance change in a signal line caused by a switching means and receiving an output from the second device.

At this time, the voltage switching means may be configured to intermittent a predetermined voltage source or may be configured to change the value of the applied voltage itself.
Any device that can switch the voltage applied to the signal line between two or more values may be used.

The voltage detection means may be configured to detect the voltage of the signal line using a normal voltmeter or the like, or configured to detect whether a voltage equal to or higher than a predetermined reference value is applied using a comparison circuit such as a comparator.

The impedance switching means may have a configuration in which the impedance is changed by a variable resistor, or a configuration in which the connection is changed such as bypassing a resistive element or disconnecting or disconnecting a circuit, and may be any device that can switch the impedance of the circuit to two or more values.

The impedance detection means may have a configuration that detects a change in impedance as a change in current, or a configuration that detects a change in voltage based on a ratio with another bias resistor. When detecting a change in voltage, the impedance detection means may be configured to detect a change in impedance as a change in current. A comparator or the like may also be used.

[Effect]

In the present invention, for example, the voltage of the signal line is changed by the voltage switching means of the first device, and this change in voltage is detected by the voltage detection means of the second device, so that the voltage of the first device is changed. A signal is transmitted from the second device to the second device.

On the other hand, by changing the impedance of the signal line by the impedance switching means of the second device and detecting this change in impedance by the impedance detection means of the first device, a signal is transmitted from the second device to the first device. communicated.

Therefore, it is possible to transmit signals in both directions using a single signal line, which simplifies the connection, and because it is only necessary to install one system of signal transmission circuit similar to the conventional one, it is possible to reduce costs, thereby achieving the above purpose. be done.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 shows a configuration diagram of an audio system 1 for an automobile that utilizes the present invention, and this audio system I includes a tuner 2, a CD player 3, and a deck amplifier 4. .

Here 1. A signal transmission circuit 10 is provided between the tuner 2 and the CD player 3. As shown in FIG. 2, the signal transmission circuit 10 has a signal line 11 connecting the tuner 2 and the CD player 3. On the tuner 2 side of the signal line 11, a resistance element 12 with a resistance value Ro and a switch element 13 are connected. A voltage tA14 that generates a voltage E (V) is connected through the terminal.

The switch element 13 is usually formed of a transistor, and is made conductive by the gate voltage output from the tuner 2 depending on the selected state, and connects the resistor element 12 and the signal line 1.
Apply voltage E to 1. These switching elements 13 and voltage source 14 constitute a voltage switching means 15.

On the other hand, on the CD player 3 side of the signal line 11, a resistance element ↓6 having a resistance value Ri and a resistance element 17 having a resistance value Ri· are connected in series as a terminal resistance. A bypass 19 is formed between these resistance elements 16 and 17, which is grounded via a switch element formed of a transistor.
By making the switch element 18 conductive, it is possible to disable the resistance element 17 and change the termination resistance value. These resistance element 17, switch element 18, and bypass 19 constitute impedance switching means 20.

Here, the resistance value R4 of the resistance element 17 is the resistance value R4 of the resistance element 17.
The impedance Z1 of the circuit 10 is Z 1 =Ro+Ri −(1
), but when the switch element 18 is disconnected, the impedance Z2 is Z 2 =Ro+R4+Ri'L=, R4'
−(2). Therefore, when the impedance of the circuit 10 is greatly changed by switching the switch element 18 and the switch element 13 is conductive, the voltage ■ on the signal line 11 based on the switch of the switch element 18 is i and vc = E (V) ... (4)
Changes to However, when the switch element 13 is disconnected, the voltage applied to the signal line 11 is 0 (V).

A comparator 21 is connected between the signal line 11 and the resistance element 12 as an impedance detection means.

The comparator 21 connects the resistance elements 22 and 23 connected in series between the voltage source of the voltage E (V) and the ground to the (+) side of the operational amplifier 24, and also connects the signal line 11 to the (+) side of the operational amplifier 24. −) side,
When the voltage of the signal line 11 is equal to or higher than a predetermined threshold value Th, the operational amplifier 24 outputs a Lo times signal, and the voltage reaches the threshold value Thl.
The operational amplifier 24 is set to output the old signal in the following cases.

Here, the voltage on the signal line 11 due to the interruption of the impedance switching means 20 is . The change in is expressed as 2 in equations (3) and (4).
Since the threshold Th in the comparator 21 is
, the resistance values of the resistance elements 22 and 23 may be set so that i. In this embodiment, the resistance element 22 is +ARo,
The resistance element 23 is set to %Ro+R4, and therefore the threshold value Th is set to be the middle value of (3L) (41).

A comparator 25 serving as voltage detection means is connected between the signal line 11 and the resistance element 16. The comparator 25 includes a resistive element 2 in substantially the same way as the comparator 21.
6.27 and an operational amplifier 28.

Here, since the change in the voltage (■) on the signal line 11 due to the on/off of the voltage switching means 15 is between the value (3) or (4) 2 and 0 (V), the threshold value Th2 at the comparator 21 The resistance values of the resistance elements 26 and 27 may be set so that i. In this embodiment, the resistance element 26 is Ro+y2
Ri, the resistance element 27 is set to y2Ri, and the threshold value T
112 is set so that 1<0h*, and when the voltage of the signal wire 11 is above the threshold Th2, the old signal is output from the operational amplifier 28, and when it is below the threshold Th2, the operational amplifier 28 outputs the old signal. 28 is configured to output a Lo times signal.

Bidirectional signal η transmission in the signal transmission circuit 10 is performed by the voltage switching means 15, the comparator 21 as a voltage detection means, the impedance switching means 20, and the comparator 25 as an impedance detection means.

Note that the signal transfer circuit 10A provided between the CD player 3 and the deck amplifier 4 has substantially the same configuration as the signal transfer circuit IO, and the signal transfer circuit 10A is provided between the CD player 3 and the deck amplifier 4.
A signal line 11A is connected between them, and a resistance element 12A, a switch element 13A, and a voltage rA14 are connected to the CD player 3 side.
At'tI voltage switching means 15A and a comparator 21A are provided. Further, on the deck amplifier 4 side, an impedance switching means 2OA composed of a resistor element 16A, a resistor element 17A, a switch element 18A, and a bypass 19A, and a comparator 25A are provided.

Furthermore, within the CD player 3, the signal transmission circuit 1
The output of the comparator 25 of 0 is linked to the switch element 13A of the signal transfer circuit 10A, and the output of the comparator 21A of the circuit 10A is linked to the switch element 18 of the circuit 10, so that the signals from the tuner 2 and the deck amplifier 4 are transmitted to other devices. It is said that the structure can be transmitted to

In this embodiment, the operation when transmitting signals between the tuner 2 and the CD player 3 will be described.

When neither the tuner 2 nor the CD player 3 is in an operating state, the switch elements 13 and 18 are both in a non-conducting state, and the voltage on the signal line 11 is 0 (■).
The comparator 21 outputs an Ili signal, and the comparator 25 outputs an LO multiplied signal.

When the tuner 2 is put into operation, the switch element 13 is brought into conduction, and the voltage E from the voltage source 14 is applied to the series of resistance elements 12, signal line 11, and resistance elements 16-17. At this time, the voltage at the signal line 11, that is, the voltage at the comparator 2
1. The value of the voltage detected at 25 ■. becomes . At this time, since ■o is greater than the threshold value Thz, the comparator 25 outputs the Ili signal and the CD
Instructs player 3 to stop the operation. However, since the CD player 3 is not in an operating state, there is no change.

When the CD player 3 is brought into operation, the switch element 18 is rendered conductive and the impedance of the signal line 11 is changed. At this time, the voltage at the signal wire 11, that is, the value of the voltage detected by the comparators 21 and 25 (2).

becomes i. At this time, since (i)o is less than the threshold value Th, the comparator 21 outputs the Ili signal to stop the operation of the tuner 2. Therefore, switch element 1
3 is disconnected and the voltage V becomes O(V).

In this state, when the tuner 2 is activated, the switch element 13 is brought into conduction, the voltage Vc of the signal line 11 becomes i, and the old signal is output from the comparator 25 to
The operation of the D player 3 is stopped.

Further, the old signal from the comparator 25 turns on the switch element 13 of the signal transfer circuit 10A, and the Ili signal is output from the comparator 25Δ of the deck amplifier 4, instructing the deck amplifier 4 to stop its operation.

In this state, when the deck amplifier 4 is activated, the switch element 18A becomes conductive and the comparator 21
The lli signal is outputted from A to instruct the CD player 3 to stop its operation, and the switch element 18 is made conductive, so that the comparator 21 outputs an Ili signal to also stop the operation of the tuner 2.

Voltage (2) of the signal line 11 of the signal transmission circuit 10 due to switching of the switch elements 13 and 18 explained above. , S2 from the comparators 21 and 25 are shown in Table 1. In addition, in Table 1, Pl represents the switch element 13, and P2 represents the switching element 13.
indicates one day of the switch element, the state where the switch element is conductive is shown as closed, and the state where the switch element is disconnected is shown as open.

Table 1 According to this embodiment, as is clear from Table 1, the outputs S, , S, from the comparators 21 and 25 are In order to switch between lli and lo, the signal transmission circuit 10 is
Signals can be transmitted bidirectionally between the tuner 2 and the CD player 3 simply by providing a system. Therefore, in order to transmit signals bidirectionally between devices as in the past, the signal transmission circuit 34 is
Since there is no need to provide a system, cost reductions can be easily achieved, and furthermore, connection and routing can be facilitated by reducing the number of signal lines.

Note that if the switch element 13 is disconnected, the CD
Although it is not possible to transmit a signal from the player 3 to the tuner 2, in this embodiment, if the switch element 13 is disconnected, the tuner 2 is not operated, so there is no need to transmit a signal.

Further, the threshold value Th of the comparators 21 and 25.

By appropriately setting the connection of Th2 and the output of the circuit 10, it is possible to detect signals equivalent to those of conventional circuits from each comparator 21, 25, etc., so that it can be used as is in a conventional audio system.

Furthermore, the outputs of the comparators 21 and 25 are so-called logic outputs of the lit signal and the zero signal, and since the switching elements 13 and 18 are composed of transistors, their input can be performed at TTL level, so that the interface with each device, etc. It is also easy to handle.

It should be noted that the present invention is not limited to the configurations of the above-mentioned embodiments, and the present invention includes modifications within a range that can achieve the object of the present invention.

For example, in the embodiment described above, the switching element 13 and the voltage source 14 were provided as the voltage switching means 15, and the voltage applied to the circuit IO was switched between E (V) and 0 (V) by turning on and off the switching element 13. By providing another voltage source that outputs a voltage different from source 14, circuit 1 can be configured by selecting the voltage source.
The voltage applied to the circuit 10 may be changed by changing the voltage applied to 0, or the voltage may be changed by a power source that can adjust the voltage.In short, any voltage applied to the circuit 10 may be changed as long as it can be switched between two or more values.

At this time, if a voltage is always applied to the circuit 10 and only the voltage value can be changed, the situation where the signal cannot be transmitted because no voltage is applied to the circuit 10 as in the above embodiment will be eliminated, and the signal will always be transmitted. It can be communicated in both directions.

Also, depending on the voltage applied to the circuit 10, the comparator 21
, 25 needs to be adjusted, this can be easily achieved by changing the voltages of the comparators 21 and 25 in accordance with the voltage of the circuit IO.

Further, the impedance switching means 20 includes a resistive element 17,
Although the switch element 18 and the bypass 19 are connected in parallel, a variable resistor or the like may be used to change the impedance, and in short, any structure that can switch the impedance of the circuit 10 to two or more values is sufficient.

Although the voltage detection means and the impedance detection means were formed by the comparators 21 and 25, other structures may be used as long as they can detect voltage.

However, if the comparators 21 and 25 are used as in the above embodiment, there is an advantage that the old signal and Lo signal can be outputted according to the detected voltage and used for controlling each device.

Furthermore, the signal transmission circuit 10. IOA can be used not only for audio systems but also for signal transmission between multiple devices such as AV systems. Furthermore, it can be used for signal transmission within one device, and the first device and second device in the present invention may be any functional parts that require mutual signals, and can be used in a wide range of applications. It is possible.

〔Effect of the invention〕

As described above, the present invention provides an unprecedented bidirectional signal transmission circuit that can transmit signals in both directions using a single signal line, simplify connections, and reduce costs. be able to.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing a signal transmission circuit 10, and FIG. 3 is a circuit diagram showing a conventional example. ■... Audio system, 2... Tuner which is the first device, 3... CD player which is the second device,
10. IOA...signal transmission circuit, 11. IIA...
Signal line, 13.13A, 1B, 18A... Switch element, 14.14A... Voltage source, 15.15A... Voltage switching means, 17.17A... Resistance element, 19, 19
A... Bypass, 20.20A... Impedance switching means, 21... Comparator as impedance detection means, 25... Comparator as voltage detection means. Patent applicant Suzuki Automobile Industry Co., Ltd.

Claims (1)

[Claims] (1) A signal transmission circuit that transmits signals bidirectionally by a single signal line connecting a first and second device, wherein the signal line is connected to the first device according to the output of the device. a voltage switching means for changing the voltage applied to the second device, and the second device is provided with a voltage detection means for detecting a voltage change in the signal line caused by the voltage switching means and receiving the output of the first device; The second device is provided with impedance switching means for changing the impedance of the signal line according to the output of the device, and the first device is provided with impedance switching means for detecting an impedance change of the signal line due to the impedance switching means. A bidirectional signal transmission circuit characterized by comprising impedance detection means for receiving the output of the second device.