An instrument bus host communication circuit

Abstract

The utility model discloses a kind of instrument bus host communication circuit.Circuit is composed of receiving circuit, transmitting circuit, overload detection circuit and MCU.Receiving circuit can convert the current signal sent from slave into voltage signal, removes radio frequency interference through trap wave filtering, keeps pulsating component through direct current separation processing, after two-stage operational amplification enhances signal amplitude, then, it is outputted standard TTL signal to MCU through logic shaping circuit calibration level.Transmitting circuit can convert the TTL level outputted by MCU into high level and low level, which realizes master-slave communication signal transmission, and provides working power supply for slave.Overload detection circuit compares the voltage value corresponding to bus current monitored in real time with set threshold, and triggers MCU to cut off master-slave loop when exceeding threshold.The utility model is suitable for communication demand of various intelligent metering networks through optimizing signal processing procedure and integrated protection mechanism.

Description

Technical Field

[0001] This utility model relates to the field of communication technology for intelligent metering equipment, specifically to an instrument bus host communication circuit. Background Technology

[0002] The Instrument Bus (MBUS) protocol is widely used in the field of smart metering, mainly for data acquisition and remote communication of smart meters, water meters and gas meters. It is a key technical support for building smart grids, smart water systems and smart gas systems.

[0003] Existing MBUS communication technology supports both wired and wireless transmission media. Wired transmission primarily relies on one or two pairs of twisted-pair cables to establish a communication link, with data transmission rates typically ranging from 300bps to 9600bps. In terms of signal transmission mechanism, it uses level characteristic recognition to transmit digital signals; specifically, the downlink transmits voltage signals, while the uplink uses current signals for feedback. A stable voltage at both ends of the bus is defined as logic 1, and a level 12V lower is defined as logic 0. The master station sends frame data to the slave station via voltage transition pulses, and the slave station responds to the master station by outputting 11-20mA current pulses. Existing technology has the following main problems:

[0004] (1) Since the MBUS circuit relies on voltage and current analog signals for data transmission, in long-distance communication scenarios, the signal is easily affected by differential mode interference and common mode interference, which leads to bit errors in level identification, and then causes communication interruption or data transmission error.

[0005] (2) Currently, most MBUS communication circuits in the industry are built using discrete components. This method not only increases the complexity of circuit design, but also has problems such as insufficient stability and poor compatibility. It is difficult to meet the higher requirements of intelligent metering systems for communication reliability and integration, which restricts the application expansion of MBUS technology in large-scale metering networks.

[0006] Therefore, a new type of instrument bus host communication circuit is needed. Utility Model Content

[0007] To address the problems of high error rate, insufficient reliability, and limited adaptability in existing MBUS communication technology, this utility model proposes an instrument bus host communication circuit, including a receiving circuit, a transmitting circuit, an overload detection circuit, and a microcontroller unit. The receiving circuit converts the current signal transmitted by the slave device into a standard TTL signal and outputs it to the microcontroller unit. The transmitting circuit converts the TTL level output by the microcontroller unit into a corresponding high or low level and provides operating power to the slave device. The overload detection circuit monitors the voltage value corresponding to the bus current, compares it with a set threshold, and outputs an overload detection signal to the microcontroller unit to control the on / off state of the transmitting circuit. The microcontroller unit is electrically connected to the receiving circuit, the transmitting circuit, and the overload detection circuit.

[0008] Preferably, the receiving circuit sequentially includes a current-to-voltage conversion module, a notch filter module, a DC blocking module, an operational amplifier module, and a logic shaping module; the current-to-voltage conversion module converts the current signal into a voltage signal through a resistor; the notch filter module includes an inductor and capacitor branch for filtering out radio frequency interference; the DC blocking module retains the pulsating component through a capacitor; the operational amplifier module amplifies the signal amplitude through multiple stages; the logic shaping module uses a logic chip, sets a reference threshold calibration level, and outputs a standard TTL signal by comparing positive and negative input signals.

[0009] Preferably, the transmitting circuit is connected to high-level and low-level voltages, and the MBUS_TXD signal output by the microcontroller unit is converted into high-level and low-level signals through a transistor switching component, and the slave power supply path is controlled by the MBUS_CTL signal.

[0010] Preferably, the transmitting circuit has a PTC element connected in series and a TVS diode connected in parallel; the resistance of the PTC element is 4-7Ω.

[0011] Preferably, the overload detection circuit includes a threshold comparison module composed of operational amplifiers and a π-type low-pass filter module; the threshold comparison module monitors the voltage across the resistor corresponding to the current-voltage conversion module, compares it with a set threshold, and outputs an overload detection signal; the π-type low-pass filter module filters high-frequency noise in the detection signal.

[0012] Preferably, the circuit is connected to up to 256 slave devices, and the operating power of the slave devices is obtained through the transmitting circuit.

[0013] Preferably, in the receiving circuit, the current-to-voltage conversion module includes a parallel conversion resistor branch, the notch filter module includes a parallel branch composed of inductor L4 and capacitor C58, the DC blocking module includes a parallel branch of capacitor C55, and the operational amplifier module includes a first-stage operational amplifier and a second-stage operational amplifier. The amplification factor is set by a negative feedback resistor. The input terminals of both the first-stage and second-stage operational amplifiers are equipped with TVS diodes for amplitude limiting protection.

[0014] Preferably, the high level of the transmitting circuit is 30V and the low level is 18V. When the MBUS_TXD signal is high, the 30V voltage output is turned on to form logic 1, and when it is low, the 18V voltage output is turned on to form logic 0. When the MBUS_CTL signal is high, the slave power supply path is turned on, and when it is low, the path is turned off. The transmitting circuit is equipped with a series thermistor RT1 and a PTC element for overcurrent and voltage spike suppression, and a parallel TVS10 element.

[0015] Preferably, the threshold voltage of the overload detection circuit is set based on the bus rated current, and the voltage value corresponding to the bus rated current is calculated based on the number of slave devices; when the operational amplifier U12 outputs a low-level MBUS_CHK signal, the microcontroller controls the MBUS_CTL signal to switch to a low level, cutting off the power supply path of the transmitting circuit.

[0016] Preferably, the circuit further includes multiple protection mechanisms, including: overcurrent cut-off protection of the overload detection circuit, overcurrent protection of the PTC element in the transmitting circuit, voltage spike suppression protection of the TVS tube, and high-frequency noise filtering protection of the π-type low-pass filter module.

[0017] This utility model has the following beneficial effects:

[0018] (1) The receiving part of the circuit ensures signal accuracy through a multi-level signal processing mechanism: the notch filter composed of inductors and capacitors can specifically filter out radio frequency interference generated by devices such as prepaid radio frequency card meters, reducing the impact of external noise on the signal; the two-stage operational amplifier circuit accurately amplifies the weak pulsating voltage signal sent by the slave, ensuring that the signal amplitude meets the subsequent identification requirements; the logic shaping circuit added later calibrates the level of the amplified signal by setting a reference threshold, avoiding the MCU misidentification problem caused by low level floating, and finally realizes the stable conversion from current signal to standard TTL level signal, significantly reducing data errors in the communication process and ensuring the accuracy of data transmission between master and slave.

[0019] (2) The circuit design supports up to 256 slave devices connected simultaneously, and the slave devices obtain their power directly from the host transmitter, eliminating the need for separate power supply modules for the slave devices and simplifying the wiring and power supply design of the entire metering network. Whether it is a centralized meter reading scenario for smart meters, water meters, or gas meters, a unified communication link can be built through this host circuit.

[0020] (3) The integrated overload detection circuit can monitor the bus current status in real time. Through the threshold comparison mechanism composed of resistors and operational amplifiers, it can accurately identify whether there is abnormal overcurrent on the bus. Once the current exceeds the safe range, the MCU can quickly control the transmitting circuit to cut off the loop between the master and slave, so as to avoid damage to the core components of the master and slave due to overcurrent. At the same time, the PTC components connected in series and the TVS tubes connected in parallel in the circuit can further suppress voltage spikes and abnormal currents, forming a multi-protection mechanism, reducing the probability of equipment damage due to faults, and extending the service life of the entire metering and communication system.

[0021] The instrument bus host communication circuit described in this utility model improves communication quality, application scalability, equipment security, and cost control through optimized circuit structure design and functional integration. Attached Figure Description

[0022] Figure 1 This is a circuit block diagram of an embodiment of the present utility model;

[0023] Figure 2 This is an embodiment of the instrument bus receiving circuit of this utility model;

[0024] Figure 3 This is an embodiment of the instrument bus transmission circuit of this utility model;

[0025] Figure 4 This is an overload detection circuit according to an embodiment of the present invention. Detailed Implementation

[0026] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0027] This embodiment discloses a specific implementation scheme of an instrument bus master communication circuit. This circuit can be applied to data acquisition and communication scenarios of smart meters, water meters and gas meters. It can stably connect up to 256 slave devices. Through voltage-type transmission and current-type reception signal transmission mode, combined with overload protection mechanism, it achieves low bit error rate and high reliability master-slave communication.

[0028] In this embodiment, the instrument bus host communication circuit mainly consists of a receiving circuit, a transmitting circuit, an overload detection circuit, and an MCU. Figure 1 As shown, the component selection and operating logic of each part of the circuit are as follows:

[0029] I. Receiver Circuit Design and Workflow. The core function of the receiver circuit is to convert the current signal transmitted by the slave device into a TTL level signal that can be recognized by the MCU. For example... Figure 2 As shown, after the receiver is connected to the MBUS bus, it first converts the current signal from the slave device into a voltage signal through a 3.3Ω resistor R50. A TVS9 is connected in parallel across R50 to limit the voltage across R50, preventing damage to subsequent components due to excessive voltage. Inductor L4 and capacitor C58 form a notch filter to filter out potential RF EMI noise from prepaid RF card meters on the bus, reducing the impact of interference signals on subsequent processing.

[0030] The filtered signal enters capacitor C55. Utilizing the capacitor's DC-blocking and AC-passing characteristics, the DC component generated by the normal load is filtered out, retaining only the 15mA pulsating DC component generated during slave communication. This pulsating DC component first passes through TVS1, which limits the signal amplitude within the diode voltage drop range to prevent excessive amplitude from damaging the subsequent operational amplifier. Resistor R51 acts as a reset, quickly restoring the circuit to normal operation after the square wave signal ends. Capacitor C56 further filters out residual noise in the signal.

[0031] The subsequent signal enters a two-stage operational amplifier circuit: In the first-stage operational amplifier circuit, resistor R56 performs the reset function, capacitor C60 filters the noise generated during the amplification process, and resistors R58 and R59 form a negative feedback structure, setting the amplification factor to 6; In the second-stage operational amplifier circuit, resistor R60 performs the reset function, and similarly through the negative feedback formed by R58 and R59, the amplification factor is set to 9. After two stages of amplification, the voltage signal corresponding to the 15mA pulsating DC component is amplified from the initial approximately 49.5mV to 2.673V.

[0032] To prevent the amplified signal from floating low levels and causing misinterpretation by the MCU, a logic chip U2 is added in the subsequent stage of the circuit for level shaping. Resistors R30 and R7 work together to set the reference threshold for the positive input of the logic chip, and the amplified signal is connected to the negative input of the logic chip: when the negative input signal is lower than the positive reference threshold, the OUT terminal of the logic chip outputs a high level, forming a standard TTL "1" signal; when the negative input signal is higher than the positive reference threshold, the OUT terminal outputs a low level, forming a standard TTL "0" signal. Diode D2 is used to solve the level mismatch problem. Finally, the signal is transmitted to the MBUS RXD terminal of the MCU through resistor R6 to complete the reception process.

[0033] II. Transmitting Circuit Design and Workflow. For example... Figure 3 As shown, the transmitting circuit uses voltage-type signal transmission, converting the TTL level output by the MCU into a 30V high level and an 18V low level, thus realizing master-slave communication and providing power to the slave device. The key components and operating logic are as follows:

[0034] The power supply terminals of the transmitting circuit are connected to 30V and 18V respectively. The core switching components include transistors Q6, Q8, Q9, and Q10, diodes D10 and D11, thermistors RT1, TVS10, and a PTC. The PTC has a resistance of 4 to 7Ω, a rated current of 300mA at 60℃, and a rated current of 700mA at 25℃. The MBUS_CTL signal output by the MCU is the slave power switch signal: Under normal operating conditions, MBUS_CTL continuously outputs a high level, at which time Q10 conducts, which in turn drives Q9 to conduct, allowing the slave to obtain power through the MBUS bus, establishing the basis for communication; when an abnormally large current occurs on the bus, MBUS_CTL will switch to a low level, Q10 and Q9 will be cut off, cutting off the master-slave loop and protecting the slave from damage.

[0035] The MBUS_TXD signal output by the MCU controls the bus voltage switching: In steady state, MBUS_TXD outputs a high level, Q8 and Q6 are turned on, and the 30V voltage is transmitted to the MBUS bus through D10, Q9, and RT1, forming a logic "1" signal; when the master and slave are communicating, MBUS_TXD outputs a low level, Q8 and Q6 are turned off, and the 18V voltage is transmitted to the MBUS bus through D11, Q9, and RT1, forming a logic "0" signal, realizing the transmission of frame data to the slave. TVS10 is used to suppress bus voltage spikes, while PTC further enhances the circuit's overcurrent protection capability.

[0036] III. Overload Detection Circuit Design and Workflow. The overload detection circuit is used to monitor whether the bus current exceeds the safe threshold, preventing circuit components from being damaged due to overcurrent. Figure 4 As shown, the core component is operational amplifier U12, which is combined with resistors R64, R67, R70 and capacitors C61 and C62.

[0037] The core of overload detection is monitoring the voltage across R50 and obtaining the voltage value corresponding to the bus current through I / U conversion. Under normal operating conditions, the maximum bus voltage is 1.5mA multiplied by the number of slave devices, then multiplied by 3.3Ω, plus 15mA multiplied by 3.3Ω. Resistors R64 and R67 set the overload threshold voltage for U12. The actual voltage across R50 is connected to the +IN terminal of U12, and the threshold voltage is connected to the -IN terminal of U12. When the actual voltage is lower than the threshold voltage, the OUT terminal of U12 outputs a high level, i.e., MBUS_CHK is high, indicating that the bus current is normal; when the actual voltage is higher than the threshold voltage, the OUT terminal of U12 outputs a low level, i.e., MBUS_CHK is low, indicating that the bus is overloaded.

[0038] Resistor R70 and capacitors C61 and C62 form a π-type low-pass filter to filter high-frequency noise in the detection signal, preventing false triggering of overload detection due to noise interference. When MBUS_CHK outputs a low level, the MCU receives an overload signal and immediately controls MBUS_CTL to output a low level, cutting off the power supply to the transmitting circuit. The overload condition is not resolved until MBUS_CTL is restored to a high level, resuming normal communication.

[0039] The overall communication process of the instrument bus master communication circuit in this embodiment is as follows: When the instrument bus master communication circuit is working, in the slave non-communication state, each slave outputs a steady-state current of 1.5mA to the bus, and the total bus current is 1.5mA multiplied by the number of slaves. The receiving circuit converts this current into a fixed voltage, and after filtering and DC blocking, there is no pulsating component output, and the MCU does not receive any communication signal. When communication with a slave is required, the MCU outputs a voltage transition pulse between 30V and 18V through the transmitting circuit to send frame data to the target slave. After receiving the data, the target slave outputs a pulse current of 10-20mA to the bus, and the total bus current becomes 1.5mA multiplied by the number of slaves plus 15mA. The receiving circuit converts, filters, amplifies, and levels this current signal, and then outputs a standard TTL signal to the MCU, completing one data reception. Throughout the communication process, the overload detection circuit monitors the bus current in real time, and immediately triggers protection when an overload occurs to ensure stable circuit operation.

[0040] It should be noted that the functions described in this embodiment require the cooperation of software and other related programs to be fully realized; the aforementioned software and other related programs are not the technical solutions claimed by this utility model and are not within the protection scope of this utility model.

[0041] The above description is only a preferred embodiment of the present utility model. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present utility model, and these improvements and modifications should also be considered within the protection scope of the present utility model.

Claims

1. An instrument bus host communication circuit, characterized in that, The system includes a receiving circuit, a transmitting circuit, an overload detection circuit, and a microcontroller unit. The receiving circuit converts the current signal transmitted by the slave device into a standard TTL signal and outputs it to the microcontroller unit. The transmitting circuit converts the TTL level output by the microcontroller unit into a corresponding high or low level and provides operating power to the slave device. The overload detection circuit monitors the voltage value corresponding to the bus current, compares it with a set threshold, and outputs an overload detection signal to the microcontroller unit to control the on / off state of the transmitting circuit. The microcontroller unit is electrically connected to the receiving circuit, the transmitting circuit, and the overload detection circuit.

2. The instrument bus host communication circuit according to claim 1, characterized in that, The receiving circuit sequentially includes a current-to-voltage conversion module, a notch filter module, a DC blocking module, an operational amplifier module, and a logic shaping module. The current-to-voltage conversion module converts the current signal into a voltage signal through a resistor. The notch filter module includes an inductor and capacitor branch for filtering out radio frequency interference. The DC blocking module retains the pulsating component through a capacitor. The operational amplifier module amplifies the signal amplitude through multiple stages. The logic shaping module uses a logic chip, sets a reference threshold calibration level, and outputs a standard TTL signal by comparing positive and negative input signals.

3. The instrument bus host communication circuit according to claim 1, characterized in that, The transmitting circuit is connected to high and low level voltages, and converts the MBUS_TXD signal output by the microcontroller unit into high and low levels through a transistor switching component. The MBUS_CTL signal controls the on / off state of the slave power supply path.

4. The instrument bus host communication circuit according to claim 3, characterized in that, The transmitting circuit uses a PTC element in series and a TVS diode in parallel; the resistance of the PTC element is 4-7Ω.

5. The instrument bus host communication circuit according to claim 1, characterized in that, The overload detection circuit includes a threshold comparison module composed of operational amplifiers and a π-type low-pass filter module. The threshold comparison module monitors the voltage across the resistor corresponding to the current-voltage conversion module, compares it with a set threshold, and outputs an overload detection signal. The π-type low-pass filter module filters out high-frequency noise in the detection signal.

6. The instrument bus host communication circuit according to claim 1, characterized in that, The circuit is connected to up to 256 slave devices, and the operating power of the slave devices is obtained through the transmitting circuit.

7. The instrument bus host communication circuit according to claim 2, characterized in that, In the receiving circuit, the current-to-voltage conversion module includes a parallel conversion resistor branch, the notch filter module includes a parallel branch composed of inductor L4 and capacitor C58, the DC blocking module includes a parallel branch of capacitor C55, and the operational amplifier module includes a first-stage operational amplifier and a second-stage operational amplifier. The amplification factor is set by a negative feedback resistor. The input terminals of the first-stage and second-stage operational amplifiers are both equipped with TVS diodes for amplitude limiting protection.

8. The instrument bus host communication circuit according to claim 3, characterized in that, The transmitting circuit has a high level of 30V and a low level of 18V. When the MBUS_TXD signal is high, it conducts a 30V voltage output to form logic 1, and when it is low, it conducts an 18V voltage output to form logic 0. When the MBUS_CTL signal is high, it conducts the slave power supply path, and when it is low, it cuts off the path. The transmitting circuit is equipped with a series thermistor RT1 and a PTC element for overcurrent and voltage spike suppression, and a parallel TVS10 element.

9. The instrument bus host communication circuit according to claim 5, characterized in that, The threshold voltage of the overload detection circuit is set based on the bus rated current, and the voltage value corresponding to the bus rated current is calculated based on the number of slave devices. When the operational amplifier U12 outputs a low-level MBUS_CHK signal, the microcontroller controls the MBUS_CTL signal to switch to a low level, cutting off the power supply path of the transmitting circuit.

10. The instrument bus host communication circuit according to claim 1, characterized in that, The circuit also includes multiple protection mechanisms, including: overcurrent cut-off protection of the overload detection circuit, overcurrent protection of the PTC element in the transmitting circuit, voltage spike suppression protection of the TVS tube, and high-frequency noise filtering protection of the π-type low-pass filter module.

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