Three-wire system isolated RS-485 communication circuit, electric energy meter and acquisition terminal

Abstract

The utility model relates to a three-wire system isolated RS-485 communication circuit, electric energy meter and acquisition terminal, the circuit comprises an optocoupler isolation circuit, a 485 communication chip and a single-chip microcomputer, the 485 communication chip is connected with the single-chip microcomputer through the optocoupler isolation circuit, the optocoupler isolation circuit comprises a shaping circuit and an optocoupler, and the shaping circuit is connected with the single-chip microcomputer through the optocoupler isolation circuit. And the shaping circuit comprises a resistor, a triode and a capacitor, and is used for carrying out waveform shaping on the signal transmitted by the optocoupler so as to improve the communication baud rate. Communication with other modules is realized through the optical coupler isolated 485 communication circuit, so that the possibility that signals are interfered by other electrical interference can be effectively reduced, and the stability and reliability of signal transmission are improved; and a shaping circuit is added to the output end of the optocoupler, so that the signal integrity is effectively recovered, and the communication baud rate can still be stably operated at a relatively high level in extreme environments such as high and low temperatures.

Description

Technical Field

[0001] This utility model relates to the field of communication technology, specifically to a three-wire isolated RS-485 communication circuit, an energy meter, and a data acquisition terminal. Background Technology

[0002] RS-485 is a serial communication interface standard widely used in industrial automation, building automation, security monitoring, and other fields. It supports multi-point communication, enabling the connection of up to 32 traditional transceivers with unit loads within the same network. It boasts strong anti-interference capabilities and long transmission distances. Furthermore, by employing differential signaling and balanced transmission technology, RS-485 possesses strong electromagnetic interference resistance, making it ideal for use in complex industrial environments. This communication method not only guarantees long transmission distances but also provides stable and reliable data transmission in various environments. However, in practical applications of RS-485 communication circuits, several problems arise: common-mode interference and signal waveform distortion. In long-distance or multi-node scenarios, common-mode voltage exceeding the RS485 transceiver's tolerance range can cause differential signal waveform distortion, leading to data errors or equipment damage. Signal reflection and insufficient bus stability. When the bus termination resistor is not properly configured, signal reflection can cause the differential voltage in the idle state to be within a critical range, resulting in bit errors or communication interruptions. Node expansion and communication distance limitations. Standard RS485 supports 32 nodes, but due to insufficient signal attenuation and isolation performance in traditional circuits, it is difficult to expand to 128 or 256 nodes. As the number of nodes increases and the communication distance extends, signal quality is also affected. Furthermore, the optocouplers in existing RS485 communication circuits are affected by temperature, resulting in low communication baud rates and hindering effective circuit utilization. Utility Model Content

[0003] To address the aforementioned problems, this utility model provides a three-wire isolated RS-485 communication circuit, comprising an optocoupler isolation circuit, a RS-485 communication chip, and a microcontroller. The RS-485 communication chip is connected to the microcontroller via the optocoupler isolation circuit. The RS-485 communication chip includes RS485_RXD pins, RS485_TXD pins, and RS485_DE / RE pins. The microcontroller includes M_RS485_RXD pins, M_RS485_TXD pins, and M_RS485_DE / RE pins. The E / RE pin is part of the optocoupler isolation circuit, which includes a shaping circuit, a first optocoupler, and a first transistor control circuit. The shaping circuit includes a resistor, a transistor, and a capacitor. The shaping circuit is used to shape the waveform of the signal transmitted by the optocoupler to improve the communication baud rate. The positive terminal of the primary side of the first optocoupler is connected to the M_RS485_TXD pin via the first transistor control circuit. When M_RS485_TXD is low, the first transistor control circuit is turned on, the first optocoupler is turned on, and the RS485_RXD pin is low.

[0004] Based on the above scheme, the optocoupler isolation circuit also includes a second optocoupler and a second transistor. When the RS485_TXD pin sends a low-level signal, the second optocoupler is turned on, the second transistor is turned on, the M_RS485_RXD is low, and the microcontroller receives the transmitted signal from the 485 communication chip.

[0005] Based on the above scheme, the optocoupler isolation circuit also includes a third optocoupler and a second transistor control circuit. The positive terminal of the primary side of the third optocoupler is connected to the second transistor control circuit, and the negative terminal of the primary side is grounded. The emitter of the secondary side of the third optocoupler is connected to RS485_DE / RE. When M_RS485_DE / RE is high, the third optocoupler is cut off, and the RS485_DE / RE signal is low.

[0006] Based on the above scheme, the shaping circuit includes a first shaping circuit, which includes a first transistor, a first resistor, a second resistor, and a first capacitor. One end of the first resistor is connected to the secondary emitter of the first optocoupler, and the other end is connected to the base of the first transistor. The first capacitor is connected in parallel with the first resistor. One end of the second resistor is connected to the secondary emitter of the first optocoupler, and the other end is connected to the emitter of the first transistor. The emitter of the first transistor is connected to MGND.

[0007] Based on the above scheme, the shaping circuit further includes a second shaping circuit, which includes a second transistor QC1, a third resistor, a fourth resistor, and a second capacitor. One end of the third resistor is connected to the secondary emitter of the second optocoupler, and the other end is connected to the base of the second transistor. The second capacitor is connected in parallel with the third resistor. One end of the fourth resistor is connected to the secondary emitter of the second optocoupler, and the other end is connected to the emitter of the second transistor. The emitter of the second transistor is connected to MGND.

[0008] Specifically, the first transistor control circuit includes a third transistor, a twelfth resistor, and a thirteenth resistor. The collector of the third transistor is connected to the positive primary side of the first optocoupler via the twelfth resistor, the base is connected to M_RS485_TXD via the ninth resistor, the emitter is connected to DVDD, and the thirteenth resistor is connected between the emitter and base of the third transistor. The second transistor control circuit includes a fourth transistor, a fourteenth resistor, and a fifteenth resistor. The collector of the fourth transistor is connected to the positive primary side of the third optocoupler via the tenth resistor, the base is connected to M_RS485_DE / RE via the fourteenth resistor, the emitter is connected to DVDD, and the fifteenth resistor is connected between the emitter and base of the fourth transistor.

[0009] Based on the above scheme, the A pin and B pin of the 485 communication chip are connected to MGND through a first bidirectional TVS diode and a second bidirectional TVS diode, respectively, and a third bidirectional TVS diode is connected between the A pin and the B pin. The B pin of the 485 communication chip is connected to the B line through a thermistor.

[0010] On the other hand, this application provides an energy meter that uses the aforementioned three-wire isolated RS-485 communication circuit to achieve data transmission.

[0011] On the other hand, this application also provides a data acquisition terminal, characterized in that it uses the above-described three-wire isolated RS-485 communication circuit to realize data transmission.

[0012] Compared with the prior art, the beneficial effects of this utility model are as follows:

[0013] 1. Communication with other modules is achieved through optocoupler-isolated 485 communication circuits, which can effectively reduce the possibility of signal being affected by other electrical interferences and improve the stability and reliability of signal transmission;

[0014] 2. A shaping circuit is added to the output of the optocoupler to effectively restore signal integrity, so that the communication baud rate can still operate stably at a high level in extreme environments such as high and low temperatures; a transistor control circuit is set to prevent the microcontroller I / O port from being damaged due to excessive sinking current.

[0015] 3. The circuit uses bidirectional TVS diodes, capacitors, and other devices to provide protection and stability, preventing excessive voltage from damaging sensitive components. The circuit is relatively simple, inexpensive, and highly sensitive, making it highly adaptable and practical. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall structure of this utility model;

[0017] Figure 2 This invention relates to an optocoupler isolation circuit.

[0018] Figure 3 This utility model relates to a 485 communication chip and its peripheral circuit. Detailed Implementation

[0019] The present invention will be further described below with reference to the accompanying drawings:

[0020] In this utility model, unless otherwise explicitly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in this utility model can be understood according to the specific circumstances.

[0021] Existing RS-485 communication circuits employ optocoupler isolation to enhance anti-interference capabilities and improve circuit stability. However, optocouplers are inherently sensitive to temperature; their response speed decreases under high and low temperature environments, leading to signal transmission delays or distortion, which in turn limits the improvement of communication baud rates. This makes traditional optocoupler isolation solutions insufficient for some applications with high communication speed requirements, resulting in wasted circuit resources and performance limitations.

[0022] To address the aforementioned problems, this application provides a three-wire isolated RS-485 communication circuit, such as... Figure 1 As shown, the circuit includes an optocoupler isolation circuit, a 485 communication chip, and a microcontroller. The 485 communication chip is connected to the microcontroller through the optocoupler isolation circuit and is used to convert TTL level to 485 level. The optocoupler isolation circuit includes a shaping circuit and an optocoupler. The shaping circuit is used to shape the waveform of the signal after it is transmitted through the optocoupler to improve the communication baud rate.

[0023] Example 1

[0024] like Figure 2 and Figure 3 As shown, the 485 communication chip includes the RS485_RXD pin, RS485_TXD pin, RS485_DE / RE pin, VCC pin, GND pin, A pin, and B pin. The RS485_RXD pin corresponds to the DI pin of the 485 communication chip, and the RS485_TXD pin corresponds to the DO pin. RS485_RXD is used to output the differential signal received on the RS485 bus to the microcontroller, RS485_TXD is used to receive data from the microcontroller and output it to the RS485 bus, and RS485_DE / RE is used to control the operating mode of the 485 communication chip.

[0025] The microcontroller includes the M_RS485_RXD pin, the M_RS485_TXD pin, and the M_RS485_DE / RE pin. The M_RS485_RXD pin is used to receive data from the RS485 communication chip, the M_RS485_TXD pin is used to send data to the RS485 communication chip, and the M_RS485_DE / RE pin is used to control the RS485_DE / RE pin of the RS485 communication chip to switch its operating mode.

[0026] The optocoupler isolation circuit includes a first optocoupler DC6, a second optocoupler DC1, a third optocoupler DC4, a first shaping circuit, a second shaping circuit, a first transistor control circuit, and a second transistor control circuit. The optocoupler electrically isolates the microcontroller and other control units from the 485 communication chip, enhancing anti-interference capability and security, while also blocking the influence of high voltage pulses or electrostatic discharge on the system.

[0027] The first shaping circuit includes a first transistor QC2, a first resistor RC13, a second resistor RC14, and a first capacitor CC4. One end of RC13 is connected to the emitter of the secondary side of DC6, and the other end is connected to the base of QC2. CC4 is connected in parallel with RC13 to accelerate the signal. One end of RC14 is connected to the emitter of the secondary side of DC6, and the other end is connected to the emitter of QC2. The emitter of QC2 is connected to MGND.

[0028] The second shaping circuit includes a second transistor QC1, a third resistor RC4, a fourth resistor RC7, and a second capacitor CC3. One end of RC4 is connected to the emitter of the secondary side of DC1, and the other end is connected to the base of QC1. CC3 is connected in parallel with RC4. One end of RC7 is connected to the emitter of the secondary side of DC1, and the other end is connected to the emitter of QC1. The emitter of QC1 is connected to MGND.

[0029] During the experiment, it was found that without the shaping circuit, the communication baud rate of the optocoupler could only reach 9600bps under both high and low temperatures. However, with the shaping circuit, the communication baud rate could reach 19200bps under both high and low temperatures. Therefore, the shaping circuit can help restore the signal waveform after transmission through the optocoupler, reduce signal distortion, and thus support higher communication baud rates.

[0030] The positive terminal of the primary side of DC6 is connected to the M_RS485_TXD pin via the first transistor control circuit. When M_RS485_TXD is low, the first transistor control circuit is turned on, the first optocoupler is turned on, and the RS485_RXD pin is low. The positive terminal of the primary side of DC4 is connected to the second transistor control circuit, and the negative terminal is grounded. The emitter of the secondary side of DC4 is connected to RS485_DE / RE. When M_RS485_DE / RE is high, the third optocoupler is turned off, and the RS485_DE / RE signal is low. The transistor control circuit is connected between the optocoupler and the microcontroller to prevent damage to the microcontroller's I / O ports due to excessive sinking current, ensuring the stability and reliability of signal transmission.

[0031] Specifically, the first transistor control circuit includes a third transistor QC4, a twelfth resistor RC12, and a thirteenth resistor RC10. The collector of QC4 is connected to the primary positive terminal of DC6 via a ninth resistor, the base is connected to M_RS485_DE / RE via RC12, and the emitter is connected to DVDD. RC10 is connected between the emitter and base of the third transistor. The second transistor control circuit includes a fourth transistor QC3, a fourteenth resistor RC6, and a fifteenth resistor RC5. The collector of QC3 is connected to the primary positive terminal of DC4 via a tenth resistor RC8, the base is connected to M_RS485_TXD via RC6, and the emitter is connected to DVDD. RC5 is connected between the emitter and base of QC4.

[0032] When the microcontroller's M_RS485_TXD pin sends a low-level signal, QC3 turns on, then DC6 turns on, and then QC2 also turns on, pulling the RS485_RXD pin signal low. The 485 communication chip UC1 receives the signal sent by the microcontroller. When the RS485_TXD pin sends a low-level signal, DC1 turns on, QC1 turns on, M_RS485_RXD is low, and the microcontroller receives the signal sent by the 485 communication chip.

[0033] Furthermore, the optocoupler isolation circuit also includes a fifth resistor RC1, a sixth resistor RC2, a seventh resistor RC3, an eighth resistor RC11, a ninth resistor RC15, a tenth resistor RC8, and an eleventh resistor RC9. One end of RC11 is connected to the RS485_RXD signal, and the other end is connected to the secondary emitter of M+5V and DC6, respectively; one end of RC15 is connected to the collector of QC4, and the other end is connected to the primary positive terminal of DC6; one end of RC3 is connected to M+5V, and the other end is connected to the primary positive terminal of DC1; one end of RC9 is connected to MGND, and the other end is connected to RS485_DE / RE; one end of RC8 is connected to the collector of QC3, and the other end is connected to the primary positive terminal of DC4; one end of RC1 is connected to the secondary collector of DC1, and the other end is connected to the collector of QC1; the collector of QC1 is connected to RC2, and the other end of resistor RC2 is connected to M_RS485_RXD.

[0034] Working principle:

[0035] When the microcontroller's M_RS485_DE / RE pin outputs a high level, QC3 is cut off, DC4 is cut off, and the RS485_DE / RE signal is low. At this time, the 485 communication chip is in receive mode, allowing data to be transmitted from the A / B bus to the RS485_RXD pin. When the microcontroller's M_RS485_DE / RE pin outputs a low level, QC3 is turned on, DC4 is turned on, and the RS485_DE / RE signal is high. At this time, the 485 communication chip is in transmit mode, and RS485_TXD receives data sent by the microcontroller and sends it out through the A / B bus.

[0036] When in receive mode, the 485 communication chip receives the differential signal on the A / B bus data and outputs it through the RO pin (RS485_TXD) of the 485 communication chip. The signal is then transmitted to the M_RS485_RXD pin of the microcontroller through the optocoupler isolation circuit. When in transmit mode, the microcontroller sends data to the DI pin (RS485_RXD) of the 485 communication chip through the M_RS485_TXD pin. The 485 communication chip converts this data into differential signals and sends them out through the A / B bus.

[0037] Example 2

[0038] Building upon Example 1, to further enhance the anti-interference capability of the 485 communication circuit, pins A and B of the 485 communication chip are connected to MGND via a first bidirectional TVS diode DC5 and a second bidirectional TVS diode DC2, respectively. A third bidirectional TVS diode DC3 is connected between pins A and B, improving the circuit's resistance to electrical interference and enhancing its reliability and safety. Adding a TVS diode between pins A and B provides additional differential mode protection, ensuring the voltage difference between the two signal lines does not exceed a certain threshold. This helps absorb transient high-voltage pulses caused by lightning strikes, electrostatic discharge, etc., further improving system reliability while ensuring the voltage difference between lines A and B remains within a safe range, thereby reducing the possibility of data transmission errors.

[0039] The circuit also includes a third capacitor CC2, a sixteenth resistor RC16, and a seventeenth resistor RC17. CC2 is the filter and decoupling capacitor for the 485 communication chip UC1. RC16 is the pull-down resistor for pin B of the 485 chip UC1, setting a fixed low level. RC17 is the pull-up resistor for pin A of the 485 chip UC1, setting a fixed high level.

[0040] Preferably, the B pin of the 485 communication chip is connected to the B line via a thermistor to prevent high current from damaging the device and to provide an automatic recovery function; it also adapts to different temperature conditions and maintains the integrity and stability of the signal.

[0041] On the other hand, this application provides an energy meter that uses the aforementioned three-wire isolated RS-485 communication circuit to achieve data transmission, for remote data communication with external devices via RS-485 bus, and to achieve stable collection and transmission of energy information.

[0042] On the other hand, this application also provides a data acquisition terminal, characterized in that it uses the above-described three-wire isolated RS-485 communication circuit to realize data transmission, which is used to realize high-speed and reliable data acquisition and remote communication in a multi-node RS-485 bus network.

[0043] The foregoing has shown and described the basic principles and main features of this utility model. It is obvious to those skilled in the art that this utility model is not limited to the details of the above exemplary embodiments. Therefore, the embodiments should be regarded as exemplary and non-limiting. The scope of this utility model is defined by the appended claims rather than the foregoing description. Therefore, it is intended to include all changes that fall within the meaning and scope of the equivalents of the claims within this utility model.

[0044] 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 three-wire isolated RS-485 communication circuit, characterized by, The application relates to a communication circuit, which comprises an optical coupling isolation circuit, a 485 communication chip and a single-chip microcomputer, the 485 communication chip is connected with the single-chip microcomputer through the optical coupling isolation circuit, the 485 communication chip comprises an RS485_RXD pin, an RS485_TXD pin and an RS485_DE / RE pin, the single-chip microcomputer comprises an M_RS485_RXD pin, an M_RS485_TXD pin and an M_RS485_DE / RE pin, the optical coupling isolation circuit comprises a shaping circuit, a first optical coupling and a first triode control circuit, the shaping circuit comprises a resistor, a triode and a capacitor, the shaping circuit is used for performing waveform shaping on signals transmitted by the optical coupling, and the communication baud rate is improved, the anode of the primary side of the first optical coupling is connected with the M_RS485_TXD pin through the first triode control circuit, when the M_RS485_TXD is at a low level, the first triode control circuit is turned on, the first optical coupling is turned on, and the RS485_RXD pin is at a low level.

2. The three-wire isolated RS-485 communication circuit of claim 1, wherein, The optical coupling isolation circuit further comprises a second optical coupling and a second triode, when the RS485_TXD pin sends a low-level signal, the second optical coupling is turned on, the second triode is turned on, the M_RS485_RXD is at a low level, and the single-chip microcomputer receives the sending signal of the 485 communication chip.

3. The three-wire isolated RS-485 communication circuit of claim 2, wherein, The optical coupling isolation circuit further comprises a third optical coupling and a second triode control circuit, the anode of the primary side of the third optical coupling is connected with the second triode control circuit, the cathode of the primary side is grounded, the emitter of the secondary side of the third optical coupling is connected with the RS485_DE / RE, when the M_RS485_DE / RE is at a high level, the third optical coupling is cut off, and the RS485_DE / RE signal is at a low level.

4. The three-wire isolated RS-485 communication circuit of claim 3, wherein, The shaping circuit comprises a first shaping circuit, the first shaping circuit comprises a first triode, a first resistor, a second resistor and a first capacitor, one end of the first resistor is connected with the emitter of the secondary side of the first optical coupling, the other end of the first resistor is connected with the base of the first triode, the first capacitor is connected with the first resistor in parallel, one end of the second resistor is connected with the emitter of the secondary side of the first optical coupling, the other end of the second resistor is connected with the emitter of the first triode, and the emitter of the first triode is connected with MGND.

5. The three-wire isolated RS-485 communication circuit of claim 4, wherein, The shaping circuit further comprises a second shaping circuit, the second shaping circuit comprises a second triode QC1, a third resistor, a fourth resistor and a second capacitor, one end of the third resistor is connected with the emitter of the secondary side of the second optical coupling, the other end of the third resistor is connected with the base of the second triode, the second capacitor is connected with the third resistor in parallel, one end of the fourth resistor is connected with the emitter of the secondary side of the second optical coupling, the other end of the fourth resistor is connected with the emitter of the second triode, and the emitter of the second triode is connected with MGND.

6. The three-wire isolated RS-485 communication circuit of claim 3, wherein, The first triode control circuit comprises a third triode, a twelfth resistor and a thirteenth resistor, the collector of the third triode is connected to the positive pole of the original side of the first optocoupler through the twelfth resistor, the base is connected to M RS485 TXD through the ninth resistor, the emitter is connected to DVDD, and the thirteenth resistor is connected between the emitter and the base of the third triode; the second triode control circuit comprises a fourth triode, a fourteenth resistor and a fifteenth resistor, the collector of the fourth triode is connected to the positive pole of the original side of the third optocoupler through the tenth resistor, the base is connected to M RS485 DE / RE through the fourteenth resistor, the emitter is connected to DVDD, and the fifteenth resistor is connected between the emitter and the base of the fourth triode.

7. The three-wire isolated RS-485 communication circuit of claim 1, wherein, The A pin and the B pin of the 485 communication chip are connected to MGND through a first bidirectional TVS tube and a second bidirectional TVS tube respectively, a third bidirectional TVS tube is connected between the A pin and the B pin, and the B pin of the 485 communication chip is connected to the B line through a thermistor.

8. An electric energy meter, characterized by The three-wire isolated RS-485 communication circuit is used for data transmission.

9. A data acquisition terminal, characterized in that, The three-wire isolated RS-485 communication circuit is used for data transmission.

Images