An interface circuit for an extension external module

Abstract

An interface circuit for extending an external module is used for data exchange between an electric energy meter MCU and an external service module, comprising a BUCK voltage reduction module, a fold line protection module and a data communication read-only interface circuit; a power supply end of the BUCK voltage reduction module is connected with an 8V isolation power supply, the 8V isolation power supply is output by an AC-DC module, another output end of the AC-DC module is connected with a power supply end of the MCU, the BUCK voltage reduction module outputs a stable 5V voltage to an input end of the fold line protection module, an output end of the fold line protection module is connected with a power supply end of the external service module; the external service module is connected with the MCU through the data communication read-only interface circuit to carry out data reading. The application can realize reading data in the electric energy meter through the external service module, can be flexibly set according to requirements, has simple circuit, low cost, small power consumption, strong practicality and is easy to realize.

Description

Technical Field

[0001] This invention relates to external communication interfaces, and more specifically, to interface circuits for secure data exchange between an electricity meter and an external service module. Background Technology

[0002] With the increasing electricity demand from industry, agriculture, commerce, and residential life, people are trading electricity more frequently. Electricity meters, as measuring instruments for electricity transactions, have high technical requirements, demanding accuracy, stability, and long-term reliability. Most electricity meters on the market communicate via RS-485 or infrared, lacking the technology to communicate with the meter through external service modules (OSMs) such as Bluetooth or Wi-Fi.

[0003] To meet the needs of various users, an interface circuit capable of expanding external modules needs to be designed. Summary of the Invention

[0004] The purpose of this invention is to address the issue of secure data exchange between electricity meters and external service modules by proposing an interface circuit for expanding external modules. This allows the electricity meter to communicate with it using different communication methods according to customer needs. For security reasons, the circuit adopts a read-only mode, meaning the external module can only read meter data and cannot write data to the meter.

[0005] The technical solution of this invention is:

[0006] This invention provides an interface circuit for expanding external modules. This circuit is used for data exchange between the MCU of an energy meter and an external service module, including a BUCK step-down module, a line protection module, and a data communication read-only interface circuit.

[0007] The power supply terminal of the BUCK step-down module is connected to an 8V isolated power supply, which is output by the AC-DC module. The other output terminal of the AC-DC module is connected to the power supply terminal of the MCU. The BUCK step-down module outputs a stable 5V voltage to the input terminal of the broken line protection module, and the output terminal of the broken line protection module is connected to the power supply terminal of the external service module.

[0008] The external service module is connected to the MCU via a data communication read-only interface circuit to read data.

[0009] Furthermore, the BUCK step-down module includes a BUCK DC-DC chip U2P, a surface mount inductor L1P, a freewheeling diode D6P, and an external circuit consisting of several resistors and capacitors connected in series and parallel.

[0010] The input terminal of the BUCK DC-DC chip U2P is connected to an 8V power supply. The output terminal of the BUCK DC-DC chip U2P is connected in series with a freewheeling diode D6P and then grounded. At the same time, the output terminal is connected in series with a surface-mount inductor L1P and then serves as the output of the BUCK step-down module, outputting a stable 5V voltage.

[0011] Furthermore, the BUCK DC-DC chip U2P has an internal resistance of 0.9Ω, and its loss is within 0.225V when the load is 0 to 250mA. U2P stably outputs a maximum current of 600mA, and the FB pin stably outputs a voltage of 0.794V. Through the voltage divider feedback resistors R21P, R16P, and R14P, the output of the BUCK buck module is stabilized at 5V.

[0012] Furthermore, the line protection module includes a line protection chip U6, a common-mode inductor L1, a TVS protection diode D3, and an external circuit composed of several resistors and capacitors connected in series and parallel. The input terminal of the line protection chip U6 is connected to the output terminal of the BUCK step-down module. The LIMIT terminal of the line protection chip U6 is connected to ground after being connected in series with current-limiting resistors R25 and R83. The OUT terminal of the line protection chip U6 is connected to ground after being connected to the TVS protection diode D3. At the same time, this output terminal is connected to the common-mode inductor L1 and serves as the output of the line protection module to output a stable 5V voltage.

[0013] Furthermore, in the peripheral circuit, the output current is set to 260mA~300mA through current-limiting resistors R25 and R83.

[0014] Furthermore, the data communication read-only interface circuit includes a high-speed optocoupler U15, an optocoupler U8, a P1 interface J21, and an overcurrent protection circuit consisting of a MOSFET Q2, a transistor Q7, and a resistor R47.

[0015] Pin 2 of the P1 interface J21 receives the data read trigger signal from the external service module. Pin 2 is connected to the input terminal of the optocoupler U8, and the output terminal of the optocoupler U8 is connected to the data read trigger signal input terminal P1 RX of the MCU.

[0016] The data output terminal P1TX of the MCU is connected to the input terminal of the high-speed optocoupler U15. The output terminal of the high-speed optocoupler U15 is connected to the collector of transistor Q7 and pin 1 of MOSFET Q2. The emitter of transistor Q7 is grounded, and the base is connected to pin 2 of MOSFET Q2. The connection point is connected in series with resistor R47 and then grounded. Pin 3 of MOSFET Q2 is used as the data output terminal and is connected to pin 5 of interface J21 of P1 to send the MCU data to the external service module.

[0017] Furthermore, the data communication read-only interface circuit also includes TVS protection tubes D1 and D2. Pin 2 of the P1 interface J21 is grounded through TVS protection tube D2, and pin 5 of the P1 interface J21 is grounded through TVS protection tube D1 to prevent interference from external high-voltage signals.

[0018] Furthermore, the data communication read-only interface circuit performs the following actions:

[0019] Pin 2 of interface J21 of P1 receives the data read trigger signal of the external service module. The data read trigger signal is high level and is sent to pin 1 of optocoupler U8. Optocoupler U8 is turned on and pin 4 of optocoupler U8 is low level and outputs to MCU.

[0020] When the MCU receives a low-level signal from pin 4 of optocoupler U8, it sends data to the external service module through pin 3 of high-speed optocoupler U15.

[0021] When the MCU sends high-level data, pins 2 and 3 of the high-speed optocoupler U15 are not conducting, pin 6 outputs high-level data, MOSFET Q2 is conducting, and pin 5 of interface J21 receives a low-level data signal.

[0022] When the MCU sends low-level data, pins 2 and 3 of the high-speed optocoupler U15 are turned on, and pin 6 outputs low-level data. MOSFET Q2 is turned off, and pin 5 of interface J21 receives a high-level data signal.

[0023] Furthermore, the high level of the data read trigger signal is 5V.

[0024] Furthermore, when pin 2 of interface J21 receives a high level from the external service module, data is sent every second; when pin 2 of interface J21 receives a low level from the external service module, data transmission stops.

[0025] The beneficial effects of this invention are:

[0026] This invention provides a circuit that enables communication with an energy meter via an external service module. It effectively overcomes the communication limitations of traditional smart energy meters, going beyond just RS485, infrared, and carrier wave communication. Compared to traditional energy meters, this invention is highly practical, easy to operate, and offers superior security. It retains the original RS485, infrared, and carrier wave communication functions of traditional energy meters and adds optional communication functionality via an external service module (OSM, such as Bluetooth or Wi-Fi), without affecting other performance aspects of the energy meter. This facilitates data reading by customers, saving time and reducing workload.

[0027] This invention enables the reading of data from the electricity meter via an external service module. It can be flexibly configured according to requirements. During communication between the external service module and the electricity meter via the P1 interface J21, the normal operation of the electricity meter will not be affected. The circuit in this invention is simple, low in cost, low in power consumption, highly practical, and easy to implement.

[0028] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0029] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the invention.

[0030] Figure 1 This is a schematic block diagram of the interface circuit of the present invention;

[0031] Figure 2 This is a circuit diagram of the BUCK step-down module in this invention;

[0032] Figure 3 This is a circuit diagram of the broken line protection module in this invention;

[0033] Figure 4 This is a circuit diagram of the data communication read-only interface circuit in this invention; Detailed Implementation

[0034] Preferred embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While preferred embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein.

[0035] An interface circuit for expanding external modules, which is used for data exchange between the energy meter MCU and the external service module, includes a BUCK step-down module, a line protection module and a data communication read-only interface circuit;

[0036] The power supply terminal of the BUCK step-down module is connected to an 8V isolated power supply, which is output by the AC-DC module. The other output terminal of the AC-DC module is connected to the power supply terminal of the MCU. The BUCK step-down module outputs a stable 5V voltage to the input terminal of the broken line protection module, and the output terminal of the broken line protection module is connected to the power supply terminal of the external service module.

[0037] The external service module is connected to the MCU via a data communication read-only interface circuit to read data.

[0038] This invention enables the reading of data from an electricity meter via an external service module (OSM, such as a Bluetooth or Wi-Fi module). An interface circuit, P1, is added to the electricity meter to expand the external module. The external service module connects to the P1 circuit interface. The external service module provides a signal to the MCU's receive pin via the P1 interface J21 in the P1 circuit. After receiving the signal from the external service module, the MCU transmits data through its transmit pin, thus transmitting the data to the external service module. The P1 circuit has overcurrent foldback protection, its power port can handle a variable load of 0-250mA, and the interface can withstand ±9kV contact discharge. When communication with the electricity meter via an external service module (OSM, such as a Bluetooth or Wi-Fi module) is required, simply connect the service module externally via the P1 port J21. The external service module provides a receive signal to the MCU, and simultaneously, the MCU sends a signal to complete the reading of the data from the electricity meter. Its principle block diagram is shown below. Figure 1 As shown in the image. This effectively solves the problem of communication between the electricity meter and the external service module.

[0039] (1) Broken line protection module: such as Figure 3 The diagram shows the circuit diagram of the line protection module. The line protection chip U6 provides a stable 5V power supply to the P1 communication circuit. Current limiting protection is achieved through resistors R25 and R83, setting the current between 260mA and 300mA. The common-mode inductor L1 effectively prevents excessive radiation. The addition of electrolytic capacitor E1 ensures that the ripple voltage meets requirements. The TVS diode D3 clamps external pulse signals to within 15V, ensuring the chip is not damaged by overvoltage. This ensures a stable and reliable power supply to the P1 communication circuit.

[0040] (2) Data communication read-only interface circuit: such as Figure 4The diagram shows the schematic of the read-only interface circuit for data communication. An external service module (OSM, such as a Bluetooth or Wi-Fi module) sends a high-level signal to pin 1 of optocoupler U8 via interface P1 (J21). At this time, optocoupler U8 is turned on. Pin 4 of optocoupler U8 is low due to its conduction. Upon receiving the low-level signal, the MCU sends data through its transmit pin (pin 3 of high-speed optocoupler U15). If the transmit signal is high, optocoupler U15 (with a communication baud rate of 115200bps) is not turned on. Pin 6 of optocoupler U15 is high because resistor R6 pulls it up to MDC5V. At this time, the collector of transistor Q7 and the gate of MOSFET Q2 are both high, meaning MOSFET Q2 is turned on. When the current flowing through MOSFET Q2 is normal, transistor Q7 is not turned on. Because MOSFET Q2 is turned on, pin 5 of interface P1 (J21) is low. When the current flowing between the DS pins of the MOSFET is too large, transistor Q7 turns on, pulling down the gate voltage of MOSFET Q2 and turning it off. Pin 5 of the P1 interface (J21) is high because MOSFET Q2 is off. If the MCU sends a low-level signal, optocoupler U15 turns on, and pin 6 of U15 is pulled low, so neither transistor Q7 nor MOSFET Q2 turns on, and pin 5 of the P1 interface (J21) is high. This allows data to be read from the meter via an external service module (OSM: such as a Bluetooth or Wi-Fi module).

[0041] In specific work:

[0042] When the Data Request Line is high at 5V, data is sent every second; when it is low, transmission stops immediately. Because the protocol requires P1 platform information (all OBIS to be sent) to be transmitted every second, a second-level interrupt is used for data transmission. The frame information is updated when the process is idle; unless the table is busy, the P1 platform information should be updated at least once every 5 seconds. When setting the P1 platform object list, the maximum byte length is checked. According to the protocol, setting a value exceeding 1024 bytes is not allowed; successful setting takes effect immediately.

[0043] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. An interface circuit for expanding external modules, characterized in that, This circuit is used for data exchange between the energy meter MCU and external service modules, including a BUCK step-down module, a line protection module, and a data communication read-only interface circuit; The power supply terminal of the BUCK step-down module is connected to an 8V isolated power supply, which is output by the AC-DC module. The other output terminal of the AC-DC module is connected to the power supply terminal of the MCU. The BUCK step-down module outputs a stable 5V voltage to the input terminal of the broken line protection module, and the output terminal of the broken line protection module is connected to the power supply terminal of the external service module. The external service module is connected to the MCU via a data communication read-only interface circuit to read data; The data communication read-only interface circuit includes high-speed optocoupler U15, optocoupler U8, P1 interface J21, and an overcurrent protection circuit consisting of MOSFET Q2, transistor Q7 and resistor R47. Pin 2 of the P1 interface J21 receives the data read trigger signal from the external service module. Pin 2 is connected to the input terminal of the optocoupler U8, and the output terminal of the optocoupler U8 is connected to the data read trigger signal input terminal P1 RX of the MCU. The MCU's data output terminal P1 TX is connected to the input terminal of high-speed optocoupler U15. The output terminal of high-speed optocoupler U15 is connected to the collector (C) of transistor Q7 and pin 1 of MOSFET Q2. The emitter (E) of transistor Q7 is grounded, and the base (B) is connected to pin 2 of MOSFET Q2. The connection point is grounded after being connected in series with resistor R47. Pin 3 of MOSFET Q2 serves as the data output terminal and is connected to pin 5 of interface J21 on P1, sending MCU data to external service modules. The data communication read-only interface circuit performs the following actions: Pin 2 of interface J21 of P1 receives the data read trigger signal of the external service module. The data read trigger signal is high level and is sent to pin 1 of optocoupler U8. Optocoupler U8 is turned on and pin 4 of optocoupler U8 is low level and outputs to MCU. When the MCU receives a low-level signal from pin 4 of optocoupler U8, it sends data to the external service module through pin 3 of high-speed optocoupler U15. When the MCU sends high-level data, pins 2 and 3 of the high-speed optocoupler U15 are not conducting, pin 6 outputs high-level data, MOSFET Q2 is conducting, and pin 5 of interface J21 receives a low-level data signal. When the MCU sends low-level data, pins 2 and 3 of the high-speed optocoupler U15 are turned on, and pin 6 outputs low-level data. MOSFET Q2 is turned off, and pin 5 of interface J21 receives a high-level data signal.

2. The interface circuit for expanding external modules according to claim 1, characterized in that, The BUCK step-down module includes a BUCK DC-DC chip U2P, a surface mount inductor L1P, a freewheeling diode D6P, and an external circuit consisting of several resistors and capacitors connected in series and parallel. The input terminal of the BUCK DC-DC chip U2P is connected to an 8V power supply. The output terminal of the BUCK DC-DC chip U2P is connected in series with a freewheeling diode D6P and then grounded. At the same time, the output terminal is connected in series with a surface-mount inductor L1P and then serves as the output of the BUCK step-down module, outputting a stable 5V voltage.

3. The interface circuit for expanding external modules according to claim 2, characterized in that, The BUCK DC-DC chip U2P has an internal resistance of 0.9Ω and its loss is within 0.225V when the load is 0~250mA. U2P can stably output a maximum current of 600mA and the FB pin can stably output a voltage of 0.794V. Through the voltage divider feedback resistors R21P, R16P, and R14P, the output of the BUCK buck module is stabilized at 5V.

4. The interface circuit for expanding external modules according to claim 1, characterized in that, The broken-line protection module includes a broken-line protection chip U6, a common-mode inductor L1, a TVS protection diode D3, and an external circuit composed of several resistors and capacitors connected in series and parallel. The input terminal of the broken-line protection chip U6 is connected to the output terminal of the BUCK step-down module. The LIMIT terminal of the broken-line protection chip U6 is connected to ground after being connected in series with current-limiting resistors R25 and R83. The OUT terminal of the broken-line protection chip U6 is connected to ground after being connected to the TVS protection diode D3. At the same time, this output terminal is connected to the common-mode inductor L1 and serves as the output of the broken-line protection module to output a stable 5V voltage.

5. The interface circuit for expanding external modules according to claim 4, characterized in that, In the external circuit, the output current is set to 260mA~300mA through current-limiting resistors R25 and R83.

6. The interface circuit for expanding external modules according to claim 1, characterized in that, The data communication read-only interface circuit also includes TVS protection tubes D1 and D2. Pin 2 of the P1 interface J21 is grounded through TVS protection tube D2, and pin 5 of the P1 interface J21 is grounded through TVS protection tube D1 to prevent interference from external high voltage signals.

7. The interface circuit for expanding external modules according to claim 1, characterized in that, The high level of the data read trigger signal is 5V.

8. The interface circuit for expanding external modules according to claim 1, characterized in that, When pin 2 of interface J21 receives a high level from the external service module, data is transmitted; when pin 2 of interface J21 receives a low level from the external service module, transmission stops.

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