Communication circuits, interfaces and testing systems

Abstract

This utility model discloses a communication circuit, interface, and testing system. The communication circuit includes a switching module, a first coupling module, a second coupling module, and a communication interface module. The first and second coupling modules establish current loop communication with a first external device, respectively. The switching module switches the connection between the first and second coupling modules and the first external device. The communication interface module converts the communication signal between the second external device and either the first or second coupling module. This utility model's communication circuit, interface, and testing system, by integrating the first and second coupling modules and using the switching module to switch the connection between the first and second coupling modules and the first external device, facilitates flexible switching between different communication modes. By adding a control module, it can also adapt to more communication protocols and meet more testing scenarios.

Description

Technical Field

[0001] This utility model belongs to the field of communication technology, specifically relating to a communication circuit, interface and testing system. Background Technology

[0002] The indoor and outdoor units of an air conditioner need to communicate with each other, typically using a common neutral (N) current loop communication circuit. For example... Figure 1 As shown, the output terminal of the indoor unit communication circuit and the input terminal of the outdoor unit communication circuit can be connected through the signal line (SIG line), and the input terminal of the indoor unit communication circuit and the output terminal of the outdoor unit communication circuit can be connected through the neutral line. Meanwhile, the current in the loop is provided by the live wire (L line) on the high-voltage side after voltage reduction.

[0003] Currently, there are two common communication modes between indoor and outdoor air conditioning units: one is... Figure 1 As shown in (a), if the communication loop is powered on the indoor unit side, then a live wire power supply is not required on the communication loop on the outdoor unit side. Another example is... Figure 1 As shown in (b), the communication loop is powered by a live wire introduced on the outdoor unit side, while there is no power supply introduced on the communication loop on the indoor unit side.

[0004] When testing the performance of an air conditioner outdoor unit, communication is required. The testing equipment is typically built with a PLC, but the PLC cannot communicate directly with the outdoor unit; a communication module is needed between them. Given the two communication modes between indoor and outdoor units, two different communication modules need to be designed between the PLC and the outdoor unit. When testing outdoor units from different manufacturers, these communication modules need to be repeatedly switched, making it impossible to achieve good compatibility with different outdoor units.

[0005] The information disclosed in this background section is intended only to enhance the understanding of the overall background of this utility model and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Utility Model Content

[0006] The purpose of this invention is to provide a communication circuit, interface, and testing system that is compatible with different current loop communication modes.

[0007] To achieve the above objectives, the technical solution provided by a specific embodiment of this utility model is as follows:

[0008] A communication circuit includes a switching module, a first coupling module, a second coupling module, and a communication interface module. The first coupling module and the second coupling module are connected to a first external device through the switching module to establish current loop communication with the first external device respectively. The switching module is used to switch the connection between the first coupling module, the second coupling module, and the first external device. The communication interface module is connected to the first coupling module, the second coupling module, and the second external device, and is used for communication signal conversion between the second external device and the first coupling module or the second coupling module.

[0009] In one or more embodiments of this utility model, the first coupling module includes a first optocoupler unit, a second optocoupler unit, and a first current loop. An optical switch in the first optocoupler unit and a light-emitting device in the second optocoupler unit are connected in series in the first current loop. The first current loop is connected to a first external device via a switching module. The light-emitting device in the first optocoupler unit is connected to a communication interface module to emit light based on the control of the communication interface module. The optical switch in the second optocoupler unit is connected to the communication interface module to transmit communication signals based on its own on / off state. The second coupling module includes a third optocoupler unit, a fourth optocoupler unit, a second current loop, and a power processing unit. The optical switch in the third optocoupler unit and the light-emitting device in the fourth optocoupler unit are connected in series in the second current loop. The second current loop is connected to the first external device via a switching module. The light-emitting device in the third optocoupler unit is connected to the communication interface module to emit light based on the control of the communication interface module. The optical switch in the fourth optocoupler unit is connected to the communication interface module to transmit communication signals based on its own on / off state. The power processing unit is connected to the second current loop to provide power to the second current loop.

[0010] In one or more embodiments of this utility model, the communication circuit further includes a switching unit, wherein the switching unit and the light-emitting device in the first optocoupler unit are connected in series between the power supply voltage and the ground voltage, and the switching unit and the light-emitting device in the third optocoupler unit are connected in series between the power supply voltage and the ground voltage. The switching unit is connected to the communication interface module to turn on or off based on the control of the communication interface module, and to control the light-emitting devices in the first optocoupler unit and the third optocoupler unit to emit light.

[0011] In one or more embodiments of the present invention, the first coupling module further includes a current limiting unit and / or an anti-reverse current unit connected in series in the first current loop; and / or the second coupling module further includes a filtering unit connected to the second current loop.

[0012] In one or more embodiments of this utility model, the power processing unit is connected to the live wire of a first external device to obtain power.

[0013] In one or more embodiments of this utility model, the communication circuit further includes a control module, which is connected to a first coupling module, a second coupling module, and a communication interface module. The control module is used for communication signal conversion between the communication interface module and the first coupling module or the second coupling module.

[0014] In one or more embodiments of this utility model, the switching module includes one or more of a relay, a transistor switch, a MOSFET switch, and a mechanical switch.

[0015] In one or more embodiments of this utility model, the communication interface module includes an RS485 chip or an RS232 chip.

[0016] A specific embodiment of this utility model also provides a communication interface, including a circuit board on which the above-mentioned communication circuit is disposed.

[0017] A specific embodiment of this utility model also provides a testing system for an air conditioner, including a switching module, a first coupling module, a second coupling module, a communication interface module, and a testing machine. The first coupling module and the second coupling module are connected to the air conditioner through the switching module to establish current loop communication with the air conditioner respectively. The switching module is used to switch the connection between the first coupling module, the second coupling module, and the device under test. The communication interface module is connected to the first coupling module, the second coupling module, and the testing machine, and is used for communication signal conversion between the testing machine and the first coupling module or the second coupling module.

[0018] Compared with existing technologies, the communication circuit, interface, and testing system of this invention integrates a first coupling module and a second coupling module, and uses a switching module to switch the connection between the first coupling module, the second coupling module, and the first external device, facilitating flexible switching between different communication modes. By adding a control module, it can also adapt to more communication protocols and meet more testing scenarios. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 (a) is a schematic diagram of the communication principle between indoor and outdoor units of an air conditioner in the prior art.

[0021] Figure 1(b) is another communication principle diagram between indoor and outdoor units of an air conditioner in the prior art.

[0022] Figure 2 This is a circuit diagram of the communication circuit in one embodiment of the present invention.

[0023] Figure 3 This is a schematic diagram of the working principle of the communication circuit in one embodiment of the present invention.

[0024] Figure 4 This is another schematic diagram of the working principle of the communication circuit in one embodiment of the present invention. Detailed Implementation

[0025] To enable those skilled in the art to better understand the technical solutions in this disclosure, the technical solutions in the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this disclosure.

[0026] The terms "coupled," "connected," or "linked" in this specification include both direct and indirect connections. Indirect connections are those made through an intermediate medium, such as those made through an electrically conductive medium, which may have parasitic inductance or capacitance. Indirect connections may also include connections made through other active or passive devices to achieve the same or similar functional purpose, such as connections through switches, follower circuits, or other circuits or components. Furthermore, in this specification, terms such as "first" and "second" are primarily used to distinguish one technical feature from another, and do not necessarily require or imply any actual relationship, quantity, or order between these technical features.

[0027] In the detailed description of this specification, reference is made to the accompanying drawings, which form a part thereof, wherein like reference numerals always denote like parts, and wherein exemplary embodiments are shown by way of example that may be implemented. It should be understood that other embodiments may be utilized, and structural or logical changes may be made, without departing from the scope of this application. Therefore, the following detailed description should not be considered limiting.

[0028] The various operations in the specification may be described sequentially as multiple discrete actions or operations in a manner most conducive to understanding the claimed subject matter. However, the order of description should not be construed as implying that these operations must be sequentially related. Specifically, these operations may not be performed in the order presented. The described operations may be performed in a different order than in the described embodiments. Various additional operations may be performed in additional embodiments and / or the described operations may be omitted.

[0029] For the purposes of this application, the phrase "A and / or B" means (A), (B), or (A and B). For the purposes of this application, the phrase "A, B and / or C" means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B and C).

[0030] Various components and devices may be mentioned or shown in the singular form herein, but only for the convenience of discussion, and any element mentioned in the singular form may include multiple such elements as taught herein.

[0031] The description uses the phrases "in one embodiment," "in other embodiments," or "in some embodiments," each of which can refer to one or more of the same or different embodiments. Furthermore, the terms "comprising," "including," "having," etc., used in relation to embodiments of this application are synonymous.

[0032] Example 1

[0033] like Figure 2 As shown, the communication circuit in one embodiment of this utility model includes a switching module 10, a first coupling module 20, a second coupling module 30, a control module 40, and a communication interface module 50.

[0034] The first coupling module 20 and the second coupling module 30 are connected to the first external device via a switching module 10 to establish current loop communication with the first external device, respectively. The switching module 10 is used to switch the connection between the first coupling module 20, the second coupling module 30, and the first external device. The control module 40 is connected to the first coupling module 20, the second coupling module 30, and the communication interface module 50. The control module 40 is used for communication signal conversion between the communication interface module 50 and either the first coupling module 20 or the second coupling module 30. The communication interface module 50 is connected to the second external device and is used for communication signal conversion between the second external device and the control module 40.

[0035] In one embodiment, the first external device is an outdoor unit of an air conditioner, and the outdoor unit of the air conditioner generally communicates with the indoor unit of the air conditioner through a common neutral line (N line) current loop.

[0036] In one embodiment, the second external device is a PLC (Programmable Logic Controller). Although a PLC can generally support a variety of fieldbuses and standard communication protocols, it cannot communicate directly with the first external device through a common neutral line current loop.

[0037] like Figure 2As shown, in one embodiment, the switching module 10 includes a relay. The relay has two switches, namely switch K1 and switch K2. The first terminal of switch K1 is connected to the signal line SIG in the first external device, and the first terminal of switch K2 is connected to the neutral line N in the first external device. When the relay coil is not energized, the second terminal of switch K1 and switch K2 are both connected to the first coupling module 20. When the relay coil is energized, the second terminal of switch K1 and switch K2 are both connected to the second coupling module 30.

[0038] Preferably, the switching module 10 may further include a diode V3, a transistor V4, and a resistor R22. The first terminal of the relay coil and the cathode of diode V3 are connected to the power supply voltage. The second terminal of the relay coil and the anode of diode V3 are connected to the collector of transistor V4. The emitter of transistor V4 is connected to ground. The base of transistor V4 is connected to the first terminal of resistor R22. The second terminal of resistor R22 is used to receive the switching control signal IN. Transistor V4 is an NPN transistor. When the switching control signal IN is low, the relay coil is not energized; when the switching control signal IN is high, the relay coil is energized.

[0039] In other embodiments, the switching module 10 may also include one or more of transistor switches, MOSFET switches, and mechanical switches, as long as the switching function can be achieved. Those skilled in the art can construct specific circuits using transistor switches, MOSFET switches, and mechanical switches.

[0040] like Figure 2 As shown, the first coupling module 20 includes a first optocoupler unit U1, a second optocoupler unit U2, a current limiting unit, an anti-reverse current unit, and a first current loop.

[0041] In this system, the optical switch in the first optocoupler unit U1 and the light-emitting device, current-limiting unit, and anti-reverse-current unit in the second optocoupler unit U2 are all connected in series in the first current loop. The first current loop is connected to the first external device through the switching module 10. The light-emitting device in the first optocoupler unit U1 is connected to the communication interface module 50 to emit light based on the control of the communication interface module 50. The optical switch in the second optocoupler unit U2 is connected to the communication interface module 50 to transmit communication signals based on its own on / off state. The current-limiting unit is used to limit the magnitude of the current in the first current loop, and the anti-reverse-current unit is used to limit the direction of the current in the first current loop.

[0042] Specifically, the current limiting unit includes resistors R2, R3, and R4, and the anti-reverse current unit includes diode D2. The first terminal of resistor R2 is connected to the second terminal of switch K1. Resistors R3 and R4 are connected in series between the second terminal of resistor R2 and the first terminal of the optical switch of the first optocoupler unit U1. The second terminal of the optical switch of the first optocoupler unit U1 is connected to the first terminal of the light-emitting device of the second optocoupler unit U2. The second terminal of the light-emitting device of the second optocoupler unit U2 is connected to the anode of diode D2. The cathode of diode D2 is connected to the second terminal of switch K2.

[0043] Preferably, the first coupling module 20 may further include a resistor R8, a capacitor C1 and a diode D1. The resistor R8 and the capacitor C1 are connected in parallel across the two ends of the light-emitting device of the second optocoupler unit U2. The anode of the diode D1 is connected to the cathode of the diode D1, and the cathode of the diode D1 is connected to the first end of the resistor R2.

[0044] When the relay coil is not energized, the first end of resistor R2 is connected to the signal line SIG of the first external device through switch K1, and the cathode of diode D2 is connected to the neutral line N of the first external device through switch K2.

[0045] like Figure 2 As shown, the second coupling module 30 includes a third optocoupler unit U3, a fourth optocoupler unit U4, a filter unit, a second current loop, and a power processing unit.

[0046] In this system, the optical switch in the third optocoupler unit U3 and the light-emitting device in the fourth optocoupler unit U4 are connected in series in the second current loop. The second current loop is connected to the first external device through the switching module 10. The light-emitting device in the third optocoupler unit U3 is connected to the communication interface module 50 to emit light based on the control of the communication interface module 50. The optical switch in the fourth optocoupler unit U4 is connected to the communication interface module 50 to transmit communication signals based on its own on / off state. The power processing unit is connected to the second current loop to provide power to the second current loop. The filtering unit is connected to the second current loop to filter the loop.

[0047] In one embodiment, the power processing unit is connected to the live wire L in the first external device to obtain power.

[0048] For example, the power processing unit includes resistors R13, R15, R18, and R11, diodes D4 and D3, and capacitors C3 and C4. Resistors R13, R15, and R18 are connected in series between the live wire L in the first external device and the anode of diode D4. The cathode of diode D4 is connected to the first terminal of the optical switch in the third optocoupler unit U3. The anode of diode D3 is used to connect to the second terminal of switch K2, and the cathode of diode D3 is connected to the first terminal of the optical switch in the third optocoupler unit U3. Resistors R11, C3, and C4 are connected in parallel across diode D3.

[0049] The AC power on the live wire L is rectified by the power processing unit to obtain pulsating DC power, and then filtered and smoothed by a capacitor to stabilize at the required voltage value, so as to provide the DC voltage required for current loop communication.

[0050] Preferably, a diode D6 may also be provided in the second current loop. The second terminal of the optical switch in the third optocoupler unit U3 is connected to the first terminal of the light-emitting device in the fourth optocoupler unit U4, the second terminal of the light-emitting device in the fourth optocoupler unit U4 is connected to the anode of the diode D6, and the cathode of the diode D6 is used to connect to the second terminal of the switch K1.

[0051] The filter unit may include diode D5, capacitors C5, C6, and C7, and resistor R19. The anode of diode D5 is connected to the anode of diode D3, the cathode of diode D5 is connected to the anode of diode D6, capacitors C5 and C6 are connected in parallel across diode D5, and capacitor C7 and resistor R19 are connected in parallel across the light-emitting device in the fourth optocoupler unit U4.

[0052] When the relay coil is not energized, the anode of diode D3 is connected to the neutral line N of the first external device through switch K2, and the cathode of diode D6 is connected to the signal line SIG of the first external device through switch K1.

[0053] It can be seen that the first current loop and the second current loop can be connected to the neutral line N and the signal line SIG in the first external device through the switching module 10, thereby forming a current loop and establishing current loop communication.

[0054] Furthermore, the communication circuit may also include a switching unit 60. The switching unit 60 and the light-emitting device in the first optocoupler unit U1 are connected in series between the power supply voltage and the ground voltage. The switching unit 60 and the light-emitting device in the third optocoupler unit U3 are connected in series between the power supply voltage and the ground voltage. The switching unit 60 is connected to the control module 40 to turn on or off based on the control of the control module 40, and to control the light-emitting devices in the first optocoupler unit U1 and the third optocoupler unit to emit light.

[0055] Specifically, the switching unit 60 includes a transistor V2, resistors R12, R16, and R17. The first terminal of resistor R12 is connected to the power supply voltage. The second terminal of resistor R12 is connected to the first terminal of the light-emitting device in the first optocoupler unit U1 and the first terminal of the light-emitting device in the third optocoupler unit U3. The second terminals of the light-emitting devices in the first optocoupler unit U1 and the third optocoupler unit U3 are connected to the collector of transistor V2. The emitter of transistor V2 is connected to ground. The first terminal of resistor R16 is connected to the control module 40. The second terminals of resistors R16 and R17 are connected to the base of transistor V2. The second terminal of resistor R17 is connected to ground.

[0056] Among them, transistor V2 is an NPN transistor. Transistor V2 is controlled by the control module 40 to be turned on or off. When transistor V2 is turned on, the light-emitting devices in the first optocoupler unit U1 and the third optocoupler unit U3 form a path to ground and emit light. When transistor V2 is turned off, the light-emitting devices in the first optocoupler unit U1 and the third optocoupler unit U3 do not emit light.

[0057] Preferably, the communication circuit may further include an isolation unit 70, and the optical switches in the second optocoupler unit U2 and the fourth optocoupler unit U4 are connected to the control module 40 through the isolation unit 70.

[0058] Specifically, isolation unit 70 includes resistors R20 and R21 and capacitor C8. The first terminal of the optical switch in the second optocoupler unit U2 and the first terminal of the optical switch in the fourth optocoupler unit U4 are connected to the power supply voltage. The first terminals of resistors R20 and R21 are connected to the second terminals of the optical switches in the second optocoupler unit U2 and the fourth optocoupler unit U4, respectively. The second terminal of resistor R20 and the first terminal of capacitor C8 are connected to the control module 40, and the second terminal of resistor R21 and the second terminal of capacitor C8 are connected to the ground voltage.

[0059] In one embodiment, the control module 40 includes an MCU, which has flexible communication forwarding capabilities and can adapt to more other communication protocols simply by loading the corresponding software program. The switching control signal IN can also be generated by the control module 40.

[0060] In other embodiments, the control module 40 may be omitted. In this case, the first end of resistor R16, the second end of resistor R20, and the first end of capacitor C8 are directly connected to the communication interface module 50. The communication interface module 50 directly controls the communication signal conversion between the second external device and the first coupling module 20 or the second coupling module 30. The switching control signal IN can also be generated by the second external device.

[0061] In one embodiment, the communication interface module 50 includes an RS485 chip or an RS232 chip, suitable for communication with a PLC. In other embodiments, the communication interface module 50 may also use other communication interface chips.

[0062] This embodiment also provides a communication interface, including a circuit board on which the above-described communication circuit is disposed.

[0063] Combination Figure 2 , 3 As shown, in actual operation, when the first external device adopts... Figure 1 When the communication mode of the outdoor unit of the air conditioner is in (a), the first coupling module 20 needs to be connected to the first external device through the switching module 10, so that the first current loop is connected to the neutral line N and the signal line SIG in the first external device to establish current loop communication.

[0064] In this scenario, when the first external device needs to send a signal to the second external device, the control module 40 first controls the transistor V2 to conduct, keeping the light-emitting device in the first optocoupler unit U1 illuminated and the optical switch in the first optocoupler unit U1 in a conducting state. Then, in the first external device, if the optical switch in the transmitting optocoupler is opened, the current loop closes, the light-emitting device in the second optocoupler unit U2 is energized and illuminates, the optical switch in the second optocoupler unit U2 closes, and the receiving end of the control module 40 receives a high-level signal. If the optical switch in the transmitting optocoupler is opened, the current loop breaks, the light-emitting device in the second optocoupler unit U2 does not illuminate, the optical switch in the second optocoupler unit U2 opens, and the receiving end of the control module 40 receives a low-level signal. This achieves the transmission of communication signals from the first external device to the control module 40. Then, the control module 40 and the communication interface module 50 convert the high and low level signals into a communication signal format that the second external device can process.

[0065] Similarly, when the second external device needs to send a signal to the first external device, the first external device will first control the transmitting optocoupler to remain on. Then, the second external device will control the switching unit 60 through the control module 40 and the communication interface module 50, thereby controlling the on / off state of the optical switch in the first optocoupler unit U1, so as to transmit the signal to the first external device.

[0066] Combination Figure 2 , 4 As shown, in actual operation, when the first external device adopts... Figure 1In the communication mode of the outdoor unit of the air conditioner in (b), the second coupling module 30 needs to be connected to the first external device through the switching module 10, so that the second current loop is connected to the neutral line N and the signal line SIG in the first external device to establish current loop communication. At the same time, the power processing unit is also connected to the live wire L in the first external device, rectifies the AC power on the live wire L to obtain pulsating DC power, and then smooths the voltage through capacitor filtering to provide the DC voltage required for current loop communication.

[0067] In this case, the specific current loop communication process is as follows: Figure 3 The communication process is the same in the cases shown, and its principle will not be elaborated here.

[0068] In summary, by integrating the first coupling module 20 and the second coupling module 30, and using the switching module 10 to switch the connection between the first coupling module 20, the second coupling module 30, and the first external device, flexible switching between different communication modes is facilitated. Adding the control module 40 further enables adaptation to more communication protocols and meets a wider range of testing scenarios.

[0069] Example 2

[0070] Based on the same design principles as Embodiment 1, this embodiment also provides a test system for air conditioners, including a switching module, a first coupling module, a second coupling module, a control module, a communication interface module, and a test machine. The first and second coupling modules are connected to the air conditioner via the switching module to establish current loop communication with the air conditioner, respectively. The switching module is used to switch the connection between the first and second coupling modules and the device under test. The control module is connected to the first and second coupling modules and the communication interface module, and is used for communication signal conversion between the communication interface module and either the first or second coupling module. The communication interface module is connected to the test machine, and is used for communication signal conversion between the test machine and the control module.

[0071] Specifically, the specific structure, connection method, and working principle of the switching module, first coupling module, second coupling module, and communication interface module in this embodiment are the same as those of the switching module 10, first coupling module 20, second coupling module 30, and communication interface module 50 in Embodiment 1. The communication part of the air conditioner in this embodiment is the same as the communication part of the first external device described in Embodiment 1 in terms of specific structure, connection method, and working principle. Similarly, the communication part of the test machine in this embodiment is the same as the communication part of the second external device described in Embodiment 1 in terms of specific structure, connection method, and working principle.

[0072] In other embodiments, a control module may not be provided. In this case, the first coupling module and the second coupling module are directly connected to the communication interface module, and the communication signal conversion between the second external device and the first coupling module or the second coupling module can be directly controlled through the communication interface module.

[0073] Preferably, the test system may also include a switching unit and / or an isolation unit. The switching unit in this embodiment has the same specific structure, connection method, and working principle as the switching unit 60 described in Embodiment 1. The isolation unit in this embodiment has the same specific structure, connection method, and working principle as the isolation unit 70 described in Embodiment 1.

[0074] It will be apparent to those skilled in the art that this disclosure is not limited to the details of the exemplary embodiments described above, and that this disclosure can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of this disclosure is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within this disclosure. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0075] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A communication circuit, characterized in that, The device includes a switching module, a first coupling module, a second coupling module, and a communication interface module. The first coupling module and the second coupling module are connected to a first external device through the switching module to establish current loop communication with the first external device. The switching module is used to switch the connection between the first coupling module, the second coupling module, and the first external device. The communication interface module is connected to the first coupling module, the second coupling module, and the second external device. The communication interface module is used for communication signal conversion between the second external device and the first coupling module or the second coupling module.

2. The communication circuit according to claim 1, characterized in that, The first coupling module includes a first optocoupler unit, a second optocoupler unit, and a first current loop. The optical switch in the first optocoupler unit and the light-emitting device in the second optocoupler unit are connected in series in the first current loop. The first current loop is connected to a first external device through a switching module. The light-emitting device in the first optocoupler unit is connected to a communication interface module to emit light based on the control of the communication interface module. The optical switch in the second optocoupler unit is connected to the communication interface module to transmit communication signals based on its own on / off state. The second coupling module includes a third optocoupler unit, a fourth optocoupler unit, a second current loop, and a power processing unit. The optical switch in the third optocoupler unit and the light-emitting device in the fourth optocoupler unit are connected in series in the second current loop. The second current loop is connected to a first external device through a switching module. The light-emitting device in the third optocoupler unit is connected to a communication interface module to emit light based on the control of the communication interface module. The optical switch in the fourth optocoupler unit is connected to the communication interface module to transmit communication signals based on its own on / off state. The power processing unit is connected to the second current loop to provide power to the second current loop.

3. The communication circuit according to claim 2, characterized in that, The communication circuit also includes a switching unit. The switching unit and the light-emitting device in the first optocoupler unit are connected in series between the power supply voltage and the ground voltage. The switching unit and the light-emitting device in the third optocoupler unit are connected in series between the power supply voltage and the ground voltage. The switching unit is connected to the communication interface module to turn on or off based on the control of the communication interface module, and to control the light-emitting devices in the first optocoupler unit and the third optocoupler unit to emit light.

4. The communication circuit according to claim 2, characterized in that, The first coupling module further includes a current limiting unit and / or an anti-reverse current unit connected in series in the first current loop; and / or The second coupling module also includes a filter unit connected to the second current loop.

5. The communication circuit according to claim 2, characterized in that, The power processing unit is connected to the live wire in the first external device to obtain power.

6. The communication circuit according to claim 1, characterized in that, The communication circuit also includes a control module, which is connected to the first coupling module, the second coupling module, and the communication interface module. The control module is used for communication signal conversion between the communication interface module and the first coupling module or the second coupling module.

7. The communication circuit according to claim 1, characterized in that, The switching module includes one or more of the following: relay, transistor switch, MOSFET switch, and mechanical switch.

8. The communication circuit according to claim 1, characterized in that, The communication interface module includes an RS485 chip or an RS232 chip.

9. A communication interface, characterized in that, It includes a circuit board, on which a communication circuit as described in any one of claims 1 to 8 is provided.

10. A testing system for air conditioners, characterized in that, The device includes a switching module, a first coupling module, a second coupling module, a communication interface module, and a test machine. The first and second coupling modules are connected to an air conditioner through the switching module to establish current loop communication with the air conditioner respectively. The switching module is used to switch the connection between the first and second coupling modules and the device under test. The communication interface module is connected to the first and second coupling modules and the test machine, and is used for communication signal conversion between the test machine and the first or second coupling module.

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