Two-wire system isolated 485 communication circuit

Abstract

The utility model relates to the technical field of 485 communication circuits, provides a two-wire system isolated 485 communication circuit, and aims to solve the problems that the conventional RS-485 communication circuit is easily interfered by electrical noise, has potential difference and current surge and the like in industrial control and other field environments and enhance the stability and safety of a system. The circuit comprises a resistor, a capacitor, a triode, an optocoupler, a TVS (Transient Voltage Suppressor) tube, a 485 communication chip and other key elements. Effective isolation of signals is achieved through the optocoupler, other electrical interference is reduced, and stability of data transmission is ensured. And a TVS tube added in the circuit design provides overvoltage protection, so that the circuit is prevented from being damaged by electrostatic discharge or electrical surge. And the capacitor C6 is used for decoupling the power supply, so that the voltage of the power supply can be stabilized, and the relay can work stably when the power supply fluctuates. The circuit provided by the utility model is simple in design and low in cost, maintains high sensitivity and strong adaptability, and has very high practicability and wide application prospect.

Description

Technical Field

[0001] The utility model relates to the technical field of 485 communication circuits, in particular to a two-wire isolated 485 communication circuit. Background Art

[0002] The technical background of RS-485 communication technology can be traced back to the 1980s. With the rapid development of microelectronics and communication technologies, the industry has a growing demand for long-distance, multi-node, low-cost serial communication interfaces. Prior to this, serial communication standards such as RS-232 have been widely used in personal computers and peripheral devices, but due to their limited transmission distance, small number of nodes, and electrical characteristics that are not suitable for long-line transmission, they cannot meet the special needs of industrial automation, building automation and other fields.

[0003] In 1983, the American Electronics Industry Association released the EIA-485 standard, which is now the RS-485 standard. The RS-485 standard is based on the principle of differential signal transmission, using two signal lines (usually called A line and B line) to transmit data, and determining the logic state by comparing the voltage difference between the two lines. This design greatly improves the signal's anti-interference ability and transmission distance, allowing up to 32 nodes (more under certain conditions) to be connected on one bus, and the transmission distance can reach more than 1,200 meters.

[0004] The RS-485 standard not only solves the problems of transmission distance and number of nodes, but its half-duplex communication mode can also adapt to the simple interaction requirements in many industrial control and data acquisition applications. In addition, the RS-485 interface is easy to interface with various microprocessors, reducing the complexity of system design. Coupled with its high cost-effectiveness, it has quickly been widely used in industrial control, process control, remote data acquisition and other fields, and is usually used in conjunction with high-level communication protocols such as Modbus to form a powerful industrial communication system.

[0005] As time goes by, RS-485 technology continues to develop and improve, and has now become one of the most commonly used communication interfaces in the global industrial automation field. It is widely used in many industries and systems such as smart buildings, energy management, transportation, security monitoring, and agricultural irrigation.

[0006] RS 485 standard is widely used in industrial control, power communication, intelligent instrumentation and other fields. However, in the field environment such as industrial control, the situation is complicated, and there is often electrical noise interfering with the transmission line. When multiple systems are interconnected, there will be a potential difference between the grounds of different systems, forming a ground loop, which will interfere with the entire system and cause catastrophic damage to the system in severe cases. There may also be high voltage or high current such as potential current surges that damage equipment or endanger personnel. Therefore, it is very necessary to isolate the RS 485 interface, and it is of great significance to optimize the performance of the isolation circuit of the RS 485 circuit. Utility Model Content

[0007] In order to solve the problems existing in the background technology, the utility model provides a two-wire isolated 485 communication circuit, which includes: resistors RW5, RW6, RW7, RW8; resistors R4, R6, R17, R18, R19, R22, R50; thermistor PTC1; capacitor C6; transistor Q1; optocouplers E1, E2; TVS tubes TVS1, TVS2; 485 communication chip U1; wherein:

[0008] Resistor R17 is used as a pull-up resistor, one end of which is connected to the RX_485 signal and the other end is connected to VCC;

[0009] Resistor R18 connects the base of transistor Q1 and the emitter of the output transistor of optocoupler E1;

[0010] Resistor R19 is used as a pull-down resistor, one end of which is grounded and the other end is connected to the input end of the optocoupler E1;

[0011] The base of transistor Q1 is connected to resistor R18, the collector is connected to the RX_485 signal, and the emitter is grounded;

[0012] The positive electrode of the input diode of the optocoupler E1 is connected to the resistor R20, and the negative electrode is connected to TX-OP;

[0013] The collector of the output transistor is connected to VCC, and the emitter is connected to resistors R18 and R19;

[0014] Resistor R50 connects VCC and the positive electrode of the optocoupler E2 input diode;

[0015] Resistor R22 connects the emitter of the output transistor of optocoupler E2 and GND485;

[0016] The collector of the output transistor of the optocoupler E2 is connected to the V_485 signal, and the emitter is connected to the resistor R22;

[0017] Pin 1 of 485 communication chip U1 is connected to signal TX_OP;

[0018] Pins 2 and 3 of the 485 communication chip U1 are connected to signal RX_OP;

[0019] Pins 4 and 5 of the 485 communication chip U1 are grounded to GND485;

[0020] Pin 6 of the 485 communication chip U1 is connected to signal A, and pin 7 is connected to signal B;

[0021] Pin 8 of 485 communication chip U1 is connected to power supply V485;

[0022] One end of capacitor C6 is connected to V_485, and the other end is grounded to GND485;

[0023] Resistor R4 connects GND485 and signal B;

[0024] One end of TVS tube TVS1 is connected to GND485, and the other end is connected to signal B;

[0025] Resistor R6 connects signal B and V_485, and TVS tube TVS2 connects signal A and GND485;

[0026] Both ends of the thermistor PTC1 are connected to signal A;

[0027] Optocouplers E1 and E2 play an isolation role to reduce the interference of other electrical signals on the signal;

[0028] Signals A and B are connected to ground GND485 through bidirectional TVS tubes to improve the circuit's ability to resist electrical interference;

[0029] The power supply V_485 is decoupled to ground through capacitor C6.

[0030] The beneficial effects achieved by the utility model are:

[0031] The utility model enhances the circuit's resistance to electromagnetic interference through isolation and TVS tube protection. Optical coupler isolation reduces the interference of other electrical signals on the signal, ensuring the stability of data transmission. The circuit is more reliable and safe in the face of potential differences, current surges, etc. The circuit design is simple and low-cost, while maintaining high sensitivity and strong adaptability, and has high practicality. Specifically:

[0032] The utility model adds optocouplers E1 and E2 to the circuit design to achieve isolation between the 485 communication circuit and other functional circuits of the smart meter, reducing the possibility of the signal being interfered with by other electrical devices and improving the electromagnetic compatibility of the system. The use of optocouplers not only isolates the circuit, but also reduces the interference of the signal during transmission, ensuring the stability and reliability of data transmission. The signal lines A and B are grounded through a bidirectional TVS tube, which effectively prevents excessive voltage from damaging sensitive components in the circuit and plays a protective role. The grounding decoupling of the power supply V_485 is achieved through capacitor C6, which helps to stabilize the power supply voltage and ensure that the relay (485 chip) can work stably even when the power supply fluctuates. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 yes Figure 1 This is the optocoupler isolation circuit of this communication circuit.

[0034] Figure 2 It is the RS485 chip and its peripheral circuit.

[0035] Figure 3 This is the functional module diagram of the 485 chip.

[0036] Figure 4 This is the operation flow chart of the two-wire isolated 485 circuit. DETAILED DESCRIPTION

[0037] The technical solution of the utility model will be clearly and completely described below in conjunction with the drawings in the utility model. In addition, the forms of the various structures recorded in the following embodiments are merely illustrative, and the utility model is not limited to the various structures recorded in the following embodiments. All other implementations obtained by ordinary technicians in this field without making creative work belong to the scope of protection of the utility model.

[0038] Reference Figure 1-4 Figure 4 The utility model provides a two-wire isolated 485 communication circuit, which includes resistors R4, R6, R17, R18, R19, R22, R50, thermistor PTC1, capacitor C6, transistor Q1, optocouplers E1, E2, TVS tubes TVS1, TVS2, and 485 communication chip U1. One end of the resistor R17 is connected to the RX_485 signal, and the other end is connected to VCC.

[0039] One end of resistor R18 is connected to the base of transistor Q1, and the other end is connected to the emitter of the output transistor of optocoupler E1. One end of resistor R19 is grounded, and the other end is connected to the input of optocoupler E1. The base of transistor Q1 is connected to resistor R18, the collector is connected to the RX_485 signal, and the emitter is grounded. The positive electrode of the input diode of optocoupler E1 is connected to resistor R20, and the negative electrode is connected to TX-OP. The collector of the output transistor is connected to VCC, and the emitter of the output transistor is connected to resistor R18 and resistor R19. One end of resistor R20 is connected to the positive electrode of the input diode of optocoupler E1. One end of resistor R50 is connected to VCC, and the other end is connected to the positive electrode of the input diode of optocoupler E2. One end of resistor R22 is connected to the emitter of the output transistor of optocoupler E2, and the other end is connected to GND485. The positive electrode of the input diode of optocoupler E2 is connected to resistor R50, and the negative electrode is connected to the TX_RS485 signal.

[0040] The collector of the output transistor of optocoupler E2 is connected to the V_485 signal, and the emitter is connected to resistor R22. Pin 1 of the 485 communication chip is connected to the signal TX_OP. Pin 2 is connected to the signal RX_OP. Pin 3 is connected to the signal RX_OP. Pin 4 is grounded to GND. Pin 5 is grounded to 485GND. Pin 6 is connected to signal A. Pin 7 is connected to signal B. Pin 8 is connected to power supply V485. One end of capacitor C6 is connected to V_485 and the other end is GND485. One end of R4 is connected to GND485 and the other end is connected to signal B. One end of TVS tube TVS1 is connected to GND485 and the other end is connected to signal B. One end of resistor R6 is connected to signal B and the other end is connected to V_485. One end of TVS tube TVS2 is connected to signal A and the other end is connected to GND485. Both ends of the thermistor are connected to signal A.

[0041] Resistor R17 is a pull-up resistor. When the output phototransistor of optocoupler E1 is turned off, VCC is used to pull up the RX_RS485 signal. Transistor Q1 is used as a switch, and its emitter is grounded. When the output phototransistor of optocoupler E1 is turned on, transistor Q1 is turned on, and the RX_RS485 signal is grounded, pulling the signal low. V485 is connected to the positive electrode of the diode at the input end of the optocoupler through resistor R20, and resistor R20 plays a role in current limiting protection. Resistor R19 is a pull-down resistor. When the output phototransistor of E1 is turned off, the base of transistor Q1 is grounded. The power supply VCC is connected to the positive electrode of the input diode of optocoupler E2 through resistor R50, and resistor R50 plays a role in current limiting protection. Resistor R22 is a pull-down resistor. When the output phototransistor of optocoupler E2 is turned off, the EX_OP signal is grounded and becomes a low level. Optocouplers E1 and E2 play an isolation role, reducing the interference of the signal received by other electrical devices and enhancing the stability of data transmission. Chip U1 is a 485 communication chip, which converts TTL level to 485 level. Pin 1 of the chip is connected to the MCU's signal TX_OP, pins 2 and 3 are connected to the MCU's signal RX_OP, and pins 4 and 5 are connected to the ground GND485.

[0042] Pin 6 is connected to signal A, which is connected to V_485 through resistor R6 to pull up, and then connected in series with thermistor PTC1 to protect. Pin 7 is connected to signal B, which is connected to GND485 through R4 to pull down. Signals A and B are connected to ground GND485 through bidirectional TVS tubes respectively, which improves the circuit's ability to resist electrical interference and improves the reliability and safety of the circuit. Pin 8 is connected to power supply V_485, which is grounded and decoupled through capacitor C6.

[0043] right Figure 1-Figure 4 The following are explained: Figure 1 This is the optocoupler isolation circuit of this communication circuit. The optocoupler isolates the 485 signal on the microcontroller side from the 485 signal on the external device. The optocoupler E1 part of the circuit. When the signal TX-OP is high, the primary side of E1 sends out a light signal to turn on both ends of the secondary side, and the transistor Q1 in the secondary circuit is turned on. The RX_485 signal is grounded through the collector and emitter of the transistor Q1 and becomes a low level. When TX-OP is high, the voltage difference between the two ends of the primary side's light-emitting diode is not enough to make it send out enough light signals, and the two ends of the secondary side are not turned on. At this time, the RX_485 signal is connected to VCC through the resistor R17 and becomes a high level. And the two signals are isolated through E1.

[0044] Partial circuit of photocoupler E2. When the TX_RS485 signal is high, the voltage difference between the two ends of the primary side is not enough to make the light-emitting diode send enough signal to turn on the secondary side. At this time, the RX-OP signal is grounded through R22 and is low. When the TX_RS485 signal is low, the voltage difference between the two ends of the primary side makes the light-emitting diode send enough signal to turn on the secondary side. At this time, RX-OP is connected to V_485 at a high level. And the two signals are isolated through E1;

[0045] Figure 2 It is the RS485 chip and its peripheral circuit. U1 is the 485 chip. Pin 1 R0 is the receiver output, connected to the signal TX-OP. Pin 4 DI is the transmitter input, connected to GND485. Pins 2 and 3 are the receiver and transmitter output enable pins, connected to the signal RX-OP. Pin 8 is the power supply pin, connected to the power supply V_485 to power the chip. Pin 6 A is the non-inverting receiver input and non-inverting transmitter output, connected to signal A. Pin 7 B is the inverting receiver input and inverting transmitter output, connected to signal B. Signal A is connected to the bidirectional TVS tube TVS2 through the pull-up resistor R6, and is connected to the outside after the thermistor PTC1 is connected in series. Signal B is connected to the outside after passing through the pull-down resistor R4 and the bidirectional TSV tube TVS1. Pin 5 GND is the ground pin, connected to GND485. ;

[0046] Figure 3This is the functional module diagram of the 485 chip. Pins 1, 2, 3, 4, and 8 are internally connected to the 8Kv HBM model, and pins 6 and 7 are internally connected to the 15Kv IEC61000 Contact for electrostatic protection. Pin 5 is grounded. The signal is converted by the RX and TX operational amplifiers to achieve communication between the microcontroller and external devices. ;

[0047] Figure 4 This is the operation flow chart of the two-wire isolated 485 circuit. After the process starts, the smart meter is powered on, the DCDC circuit outputs DC power to the 485 circuit, and the 485 circuit starts working. During communication, the 485 signal is input, and then reaches the 485 chip. The 485 chip processes the input signal and outputs it. The output signal is isolated from the microcontroller by the radio and television coupler. The isolated signal is input into the microcontroller, and then the microcontroller returns the signal. The signal is isolated by the optical coupler and then input into the 485 chip. After being processed by the 485 chip and output to the external device, the communication is completed. .

[0048] The two-wire isolated 485 communication circuit of the utility model is designed around its core components and functions to achieve two-wire isolated RS-485 communication. The following is a description of the core components and functions of the circuit:

[0049] 1.Signal isolation and transmission:

[0050] Optocouplers E1 and E2: These two optocouplers are the core isolation components of the circuit. They realize the isolated transmission of electrical signals through the photoelectric effect. Optocoupler E1 is responsible for receiving the TX_OP signal from the microcontroller and sending out a light signal through a light emitting diode (LED). After receiving the light signal, the phototransistor converts it into an electrical signal, thereby controlling the conduction and cutoff of the transistor Q1 to realize the isolated transmission of the TX_OP signal. Similarly, optocoupler E2 is responsible for the isolated reception of the RX_485 signal.

[0051] 2. Signal pull-up and pull-down:

[0052] Resistor R17: As a pull-up resistor, it ensures that the RX_485 signal can be pulled high to VCC when there is no signal.

[0053] Resistor R19: As a pull-down resistor, it ensures that when the phototransistor output by the optocoupler E1 is turned off, the base of the transistor Q1 can be pulled down to the ground, thereby controlling the signal state.

[0054] 3. Switching function of transistor Q1:

[0055] The base of transistor Q1 is connected to the output of optocoupler E1 through resistor R18, the collector is connected to the RX_485 signal, and the emitter is grounded. When the output phototransistor of optocoupler E1 is turned on, transistor Q1 is turned on, causing the RX_485 signal to be grounded, thereby pulling the signal low.

[0056] 4. Power supply and decoupling:

[0057] Capacitor C6: connected between V_485 and GND485, used for power supply decoupling to reduce the impact of power supply noise on the circuit.

[0058] Resistors R50 and R20: connected to the input terminals of optocouplers E1 and E2 respectively, play a role of current limiting protection.

[0059] 5. Anti-interference design:

[0060] TVS tubes TVS1 and TVS2: connect signals A and B to GND485 respectively to provide overvoltage protection and prevent electrostatic discharge or electrical surge from damaging the circuit.

[0061] Thermistor PTC1: connected at both ends of signal A, used for overheat protection to prevent the circuit from being damaged due to overheating.

[0062] 6.485 communication chip U1:

[0063] 485 communication chip U1: It is the core chip for realizing RS-485 communication, responsible for converting TTL level to RS-485 level to realize data sending (TX_OP) and receiving (RX_OP).

[0064] Pin 1 is connected to TX_OP for data transmission.

[0065] Pins 2 and 3 are connected to RX_OP for data reception.

[0066] Pins 4 and 5 are grounded to provide a stable reference potential.

[0067] Pin 6 and pin 7 are connected to signals A and B respectively for differential signal transmission.

[0068] Pin 8 is connected to the power supply V485 to provide working power for the chip.

[0069] 7. Bidirectional transmission of signals A and B:

[0070] Signals A and B are isolated by optocouplers and protected by TVS tubes to ensure the stability and safety of the signals during transmission.

[0071] 8. Overall control logic:

[0072] When the TX_OP signal of the microcontroller changes, the conduction and cutoff of the transistor Q1 are controlled by the optical coupler E1, thereby controlling the high and low levels of the RX_485 signal to realize data transmission.

[0073] The receiving end receives the RX_485 signal through the optocoupler E2, and transmits it to the RX_OP pin of the 485 communication chip U1 after isolation to realize data reception.

[0074] Through the above design, the utility model circuit realizes the isolation, signal transmission, anti-interference protection and power decoupling of RS-485 communication, ensuring stable communication and circuit safety in complex electrical environments.

[0075] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A two-wire isolated 485 communication circuit, characterized in that: It includes: Resistors RW5, RW6, RW7, RW8; resistors R4, R6, R17, R18, R19, R22, R50; thermistor PTC1; capacitor C6; transistor Q1; optocouplers E1, E2; TVS tubes TVS1, TVS2; 485 communication chip U1; among which: Resistor R17 is used as a pull-up resistor, one end of which is connected to the RX_485 signal and the other end is connected to VCC; Resistor R18 connects the base of transistor Q1 and the emitter of the output transistor of optocoupler E1; Resistor R19 is used as a pull-down resistor, one end of which is grounded and the other end is connected to the input end of the optocoupler E1; The base of transistor Q1 is connected to resistor R18, the collector is connected to the RX_485 signal, and the emitter is grounded; The positive electrode of the input diode of the optocoupler E1 is connected to the resistor R20, and the negative electrode is connected to TX-OP; The collector of the output transistor is connected to VCC, and the emitter is connected to resistors R18 and R19; Resistor R50 connects VCC and the positive electrode of the optocoupler E2 input diode; Resistor R22 connects the emitter of the output transistor of optocoupler E2 and GND485; The collector of the output transistor of the optocoupler E2 is connected to the V_485 signal, and the emitter is connected to the resistor R22; Pin 1 of 485 communication chip U1 is connected to signal TX_OP; Pins 2 and 3 of the 485 communication chip U1 are connected to signal RX_OP; Pins 4 and 5 of the 485 communication chip U1 are grounded to GND485; Pin 6 of the 485 communication chip U1 is connected to signal A, and pin 7 is connected to signal B; Pin 8 of 485 communication chip U1 is connected to power supply V485; One end of capacitor C6 is connected to V_485, and the other end is grounded to GND485; Resistor R4 connects GND485 and signal B; One end of TVS tube TVS1 is connected to GND485, and the other end is connected to signal B; Resistor R6 connects signal B and V_485, and TVS tube TVS2 connects signal A and GND485; Both ends of the thermistor PTC1 are connected to signal A; Optocouplers E1 and E2 play an isolation role to reduce the interference of other electrical signals on the signal; Signals A and B are connected to ground GND485 through bidirectional TVS tubes to improve the circuit's ability to resist electrical interference; The power supply V_485 is decoupled to ground through capacitor C6.

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