A circuit for implementing differential to single ended multiplexing of PLC input ports

Abstract

The utility model relates to industrial control technical field, concretely is a kind of circuit for realizing PLC input port difference and single-end multiplexing, including input terminal group, anti-reverse connection unit, filter unit, isolation unit, signal shaping unit and main control MCU, input terminal group contains A-24V, A-DIFF and A-COM terminal, anti-reverse connection unit is D1 diode, isolation unit is OC1 isolating device, signal shaping unit is U1 schmitt trigger. By switching input terminal wiring, DC24V single-end input of A-24V and A-COM cooperation can be realized, or 5V difference input of A-DIFF and A-COM cooperation;Anti-reverse connection unit avoids wiring error damage device, filter, isolation, shaping unit effectively suppresses common-mode noise and electromagnetic interference. This circuit can realize input type flexible configuration, has anti-reverse connection protection, low in cost, high stability, can adapt to short distance low noise, long distance high noise and other diversification industrial scene.

Description

Technical Field

[0001] This utility model relates to the field of industrial control technology, and in particular to a circuit for realizing differential and single-ended multiplexing of PLC input ports. Background Technology

[0002] In the field of industrial control, the input types of PLC (Programmable Logic Controller) typically include digital input types, which are specifically divided into two main types: single-ended input (including source and sink) and differential input.

[0003] The signal transmission mechanism of single-ended input is as follows: the common terminal (negative terminal) of all input signals in the signal input circuit is connected to the same grounding point (usually the COM terminal of the PLC), and the signal is transmitted through a single wire. Its advantages are simple structure and low cost. Single-ended modules usually have more input points than differential modules of the same type. However, its disadvantages are weak anti-interference ability, susceptibility to common-mode noise, and signal quality depends on the consistency of the ground potential of the two connected points. Ground potential difference or external electromagnetic interference (EMI) will directly cause signal error. Therefore, it is only suitable for low-frequency occasions with high signal voltage, short transmission distance and low noise interference.

[0004] The signal transmission mechanism of differential input is as follows: each input signal is transmitted through two wires (signal positive and signal negative). The PLC determines the signal status by comparing the voltage difference between the two wires (Vin=V+-V-), without the need for a common ground. Its advantages are that it can effectively suppress common-mode interference (external noise usually acts equally on the two signal lines, canceling each other out when calculating the voltage difference), and the two signal lines have opposite polarities, so the electromagnetic fields radiated to the outside can cancel each other out, further reducing EMI. At the same time, the timing positioning is more accurate (the logic transition is determined by the intersection of the two signals, and it is less affected by the threshold voltage). It is suitable for high-precision sensor interfaces, long-distance data transmission, or industrial environments with complex noise. However, the disadvantage is that it requires two signal lines for transmission, and each channel is equipped with an independent common line, resulting in relatively high hardware costs.

[0005] In existing technologies, traditional PLCs have fixed input types, with single-ended and differential inputs being separate and functionally limited. Corresponding terminals are fixedly connected to specific input ports, making it impossible to flexibly switch input types according to the needs of actual industrial environments (e.g., some scenarios require single-ended inputs while others require differential inputs). This makes traditional PLCs difficult to adapt to diverse application scenarios. Furthermore, traditional PLC input ports lack reverse connection protection, making them susceptible to damage to internal components and affecting system stability if wiring errors occur. In addition, since single-ended and differential inputs require separate modules, this not only increases hardware procurement costs but also enhances wiring complexity and maintenance difficulty.

[0006] Therefore, there is an urgent need for a circuit that can realize differential and single-ended multiplexing of PLC input ports, has reverse connection protection, and is low in cost, in order to overcome the shortcomings of existing technologies. Utility Model Content

[0007] The purpose of this utility model is to overcome the shortcomings of the prior art and provide a circuit for realizing differential and single-ended multiplexing of PLC input ports, so as to solve the technical problems of fixed input types, independent single-ended and differential inputs, lack of reverse connection protection devices, high cost due to the need for separate modules, and difficulty in adapting to various industrial scenarios in traditional PLCs.

[0008] The above objectives are achieved through the following technical solutions: A circuit for implementing differential and single-ended multiplexing of PLC input ports includes an input terminal group, a reverse connection protection unit, a filtering unit, an isolation unit, a signal shaping unit, and a main control MCU; The input terminal group includes an A-24V terminal, an A-DIFF terminal, and an A-COM terminal. The A-24V terminal is connected to one end of resistor R1, the A-DIFF terminal is connected to one end of resistor R3, and the A-COM terminal is connected to one end of resistor R7. The reverse connection protection unit is a D1 diode, whose anode is connected to the other end of the R7 resistor, and whose cathode is connected to a common node formed by the other end of the R1 resistor, the other end of the R3 resistor, and the ANODE terminal of the isolation unit, in order to prevent device damage caused by reverse connection when single-ended input is used. The filtering unit is connected between the common node and the signal shaping unit, as well as in the power supply circuit, and is used to perform noise filtering on the input signal and the power supply signal. The isolation unit is an OC1 isolation device, with its ANODE terminal connected to the common node, its VE terminal connected to VCC_3V3, its VO terminal connected to the input terminal of the signal shaping unit, and its GND terminal connected to GND, which is used to achieve electrical isolation between the input terminal and the control terminal. The signal shaping unit is a U1 Schmitt trigger, whose input is connected to the VO terminal of the isolation unit, the power supply is connected to VCC_3V3, the ground terminal is connected to GND, and the output is connected to the GPIO port of the main control MCU. It is used to shape the isolated signal into a standard square wave signal. The main control MCU receives the square wave signal output by the signal shaping unit through the GPIO port; By switching the wiring method of the input terminal group, a single-ended input mode can be achieved, where the A-24V terminal is connected to the resistor R1 and the A-COM terminal is connected to the resistor R7 and the diode D1, or a differential input mode can be achieved, where the A-DIFF terminal is connected to the resistor R3 and the A-COM terminal is connected to the resistor R7 and the diode D1.

[0009] Preferably, the filtering unit includes capacitors C3, C4, C1, and C2. One end of capacitor C3 is connected to the common node, and the other end is connected to GND. One end of capacitor C4 is connected to the input terminal of the signal shaping unit, and the other end is connected to GND. Capacitor C1 is connected in parallel between the power supply terminal of the U1 Schmitt trigger and GND. Capacitor C2 is connected in parallel between the VE terminal of the OC1 isolation device and GND.

[0010] Preferably, an R4 resistor is also connected between the VO terminal of the isolation unit and the input terminal of the signal shaping unit.

[0011] Preferably, the R4 resistor has a parameter of 10-5%, and an R5 resistor with a parameter of 100-1% is also connected between the output of the signal shaping unit and the GPIO port of the main control MCU.

[0012] Preferably, it further includes an indicator unit, which includes a D2 light-emitting diode and an R8 resistor. The cathode of the D2 light-emitting diode is connected to the output terminal of the U1 Schmitt trigger, and the anode is connected to GND through the R8 resistor.

[0013] Preferably, the D1 diode is of model 1N4148W.

[0014] Preferably, the OC1 isolation device is model NSI7211-DSPR.

[0015] Preferably, the U1 Schmitt trigger of the signal shaping unit is a 74HC14PW.

[0016] Preferably, the resistor R1 has a parameter of 3.3K-1%, the resistor R3 has a parameter of 150R-5%, and the resistor R7 has a parameter of 150R-5%.

[0017] Preferably, in the single-ended input mode, the voltage of the single-ended input signal is DC24V; in the differential input mode, the voltage of the differential input signal is 5V.

[0018] This utility model provides a circuit for realizing differential and single-ended multiplexing of PLC input ports. It allows for flexible multiplexing of DC24V single-ended input and 5V differential input by switching wiring, adapting to different industrial scenarios. A D1 diode provides reverse connection protection, preventing damage to components due to wiring errors. Filtering, isolation, and shaping designs suppress interference and ensure signal stability. No separate module is required, reducing cost and maintenance complexity. Furthermore, the signal status can be intuitively judged through an indicator unit, improving system reliability. Specific beneficial effects include: 1. Flexible input type configuration: By switching the wiring method of the input terminal group, the same input channel can realize DC24V single-ended input with A-24V and A-COM, or 5V differential input with A-DIFF and A-COM, which can adapt to diverse industrial scenarios such as short distance low noise and long distance high noise, and solve the defects of fixed input type of traditional PLC. 2. Features reverse connection protection: The D1 diode can effectively block the current when the single-ended input is reversed, preventing damage to the isolation unit and signal shaping unit, and improving system reliability; 3. Strong anti-interference capability: Through noise filtering of the filter unit, electrical isolation of the OC1 isolation device, and signal shaping of the U1 Schmitt trigger, common-mode noise and electromagnetic interference (EMI) can be effectively suppressed, ensuring signal transmission stability and accuracy; 4. Low cost and low complexity: No need to configure single-ended and differential input modules separately, reducing the number of hardware components, simplifying the wiring process, and reducing equipment procurement costs and maintenance complexity; 5. Intuitive status indication: The D2 LED can intuitively indicate the status of the input signal, which is convenient for on-site debugging and troubleshooting. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall structure of a circuit for realizing differential and single-ended multiplexing of PLC input ports according to the present invention. Detailed Implementation

[0020] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. The described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0021] like Figure 1 As shown, this solution provides a circuit for implementing differential and single-ended multiplexing of PLC input ports, including input terminal groups, reverse connection protection unit, filtering unit, isolation unit, signal shaping unit, and main control MCU. The structure and connection relationship of each component are as follows: The input terminal block includes an A-24V terminal, an A-DIFF terminal, and an A-COM terminal, for selectively connecting single-ended or differential input signals. Connect the A-24V terminal to one end of resistor R1 (3.3K-1%); Connect the A-DIFF terminal to one end of resistor R3 (150R-5%); Connect the A-COM terminal to one end of the R7 resistor (150R-5%); The reverse connection protection unit is a D1 diode (model 1N4148W). Its anode is connected to the other end of resistor R7, and its cathode is connected to a common node formed by the other end of resistor R1, the other end of resistor R3, and the ANODE terminal of the isolation unit. When the single-ended input wiring is reversed, the D1 diode is reverse cut off, and the current cannot flow into the subsequent circuit, thereby avoiding damage to the isolation unit and subsequent devices and achieving reverse connection protection.

[0022] The filtering unit is used to filter noise from the input signal and power supply signal to reduce external interference, including: C3 capacitor (33pF-50V): One end is connected to the common node and the other end is connected to GND, used for filtering the input signal; C4 capacitor (100pF-50V): One end is connected to the input terminal of the signal shaping unit, and the other end is connected to GND. It is used to filter the isolated signal. C1 capacitor (100nF-16V): Connected in parallel between the power supply terminal (VCC_3V3) and GND of the signal shaping unit to filter the power supply to the signal shaping unit; C2 capacitor (100nF-16V): Connected in parallel between the VE terminal (VCC_3V3) and GND of the isolation unit to filter the power supply to the isolation unit.

[0023] The isolation unit is an OC1 isolation device (model NSI7211-DSPR). Its ANODE terminal is connected to the common node, its VE terminal is connected to VCC_3V3 and connected in parallel with capacitor C2, its VO terminal is connected to one end of resistor R4 (10-5%), and its GND terminal is connected to GND. The OC1 isolation device achieves electrical isolation between the input terminal (input signal side) and the control terminal (signal shaping unit and MCU side), reducing the impact of external interference on the control terminal and improving system stability.

[0024] The signal shaping unit is a U1 Schmitt trigger (model 74HC14PW). Its input is connected to the other end of resistor R4 and one end of capacitor C4. The power supply is connected to VCC_3V3 and capacitor C1 is connected in parallel. The ground is connected to GND. The output is connected to one end of resistor R5 (100-1%). It is used to shape the non-standard signal output by the isolation unit into a standard square wave signal, so that the main control MCU can accurately identify the signal status and further reduce the introduction of interference.

[0025] The main control MCU receives the square wave signal transmitted from the other end of resistor R5 through the GPIO port, completes the identification and processing of the input signal, and realizes the control function of the PLC.

[0026] In addition, the circuit also includes an indicator unit, which includes a D2 light-emitting diode (model 19-217 / GHC-YQ1R1QY / 6T) and an R8 resistor (1K-1%). The cathode of the D2 light-emitting diode is connected to the output terminal of the U1 Schmitt trigger, and the anode is connected to GND through the R8 resistor. This is used to visually indicate the status of the input signal, which is convenient for on-site debugging and troubleshooting. At the same time, the common node is also connected to an R6 resistor (1K-1%), and the other end of the R6 resistor is connected to GND.

[0027] As a specific embodiment of this solution, the models and parameters of each component in this embodiment are as follows: Reverse polarity protection unit: D1 diode (1N4148W). Isolation unit: OC1 isolation device (NSI7211-DSPR); Signal shaping unit: U1 Schmitt trigger (74HC14PW); Indicator unit: D2 light-emitting diode (19-217 / GHC-YQ1R1QY / 6T), R8 resistor (1K-1%); Resistors: R1 (3.3K-1%), R3 (150R-5%), R6 (1K-1%), R7 (150R-5%), R2 (1K-1%), R4 (10-5%), R5 (100-1%). Capacitors: C1 (100nF-16V), C2 (100nF-16V), C3 (33pF-50V), C4 (100pF-50V); Power supply voltage: VCC_3V3 (power supply for main controller and related components); Input voltage: Single-ended input DC24V, differential input 5V; Main control MCU: Industrial-grade MCU with GPIO ports (such as STM32 series) When single-ended input is required in industrial settings (such as short-distance, low-noise scenarios, where a DC24V sensor signal is connected), the wiring method is as follows: connect the A-24V terminal to the DC24V signal terminal, connect the A-COM terminal to the common terminal, and leave the A-DIFF terminal floating (NC).

[0028] The workflow is as follows: 1. The DC24V signal flows in through the A-24V terminal, passes through resistor R1, enters the ANODE terminal, flows out through CATHODE, passes through resistor R7, and flows into the A-COM terminal; diode D1 is used for reverse cutoff. 2. After the signal from the common node is filtered by capacitor C3, it is input to the ANODE terminal of the OC1 isolation device. The OC1 preamplifier is enabled (because VCC_3V3 at the VE terminal is normal), and the output level at the VO terminal changes from high level (3.3V) to low level (0V). 3. The low-level signal at the VO terminal is filtered by resistor R4 and capacitor C4 and then enters the input terminal of the Schmitt trigger U1. U1 shapes the signal into a standard high-level (3.3V) square wave. 4. The shaped high-level signal is transmitted to resistor R5 through the output of U1, and then to the GPIO port of the main control MCU. The MCU recognizes the valid input signal. At the same time, the high level at the output of U1 causes LED D2 to conduct and light up, indicating that there is an input signal.

[0029] If the wiring is reversed (A-24V to signal negative, A-COM to signal positive): Diode D1 conducts in the forward direction, current cannot flow into the ANODE terminal, the OC1 preamp is not enabled, the VO terminal remains at a high level (3.3V), U1 outputs a low level (0V), D2 does not light up, and the MCU has no valid signal input, thus achieving reverse connection protection.

[0030] When differential input is required in industrial settings (such as long-distance, high-noise scenarios, where a 5V differential sensor signal is connected), the wiring method is as follows: connect the A-DIFF terminal to the differential signal "+" terminal, connect the A-COM terminal to the differential signal "-" terminal, and leave the A-24V terminal floating.

[0031] The workflow is as follows: The 1.5V differential signal flows in from the "+" terminal through the A-DIFF terminal, passes through resistor R3, and enters the ANODE terminal; it flows out from the CATHODE terminal, passes through resistor R7, and flows into the "-" terminal via the A-COM terminal; diode D1 (reverse cutoff). 2. The differential signal of the common node (voltage difference Vin=V+-V-=5V) is filtered by capacitor C3 and then input to the ANODE terminal of the OC1 isolation device. The OC1 preamplifier is enabled, and the output level of the VO terminal changes from high level (3.3V) to low level (0V). 3. The low-level signal at the VO terminal is filtered by resistor R4 and capacitor C4 and then enters the input terminal of the Schmitt trigger U1. U1 shapes the signal into a standard high-level (3.3V) square wave. 4. The shaped high-level signal is transmitted to resistor R5, and then to the GPIO port of the main control MCU. The MCU recognizes the valid input signal; at the same time, LED D2 turns on and illuminates, indicating that there is an input signal.

[0032] Because the differential input determines the signal by voltage difference, and the OC1 isolation device suppresses common-mode interference, accurate signal transmission can be ensured even in the presence of ground potential difference or external EMI.

[0033] The above description is only for illustrating the embodiments of this utility model and is not intended to limit this utility model. For those skilled in the art, any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the protection scope of this utility model.

Claims

1. A circuit for implementing differential and single-ended multiplexing of PLC input ports, characterized in that, It includes input terminal blocks, reverse connection protection unit, filtering unit, isolation unit, signal shaping unit, and main control MCU; The input terminal group includes an A-24V terminal, an A-DIFF terminal, and an A-COM terminal. The A-24V terminal is connected to one end of resistor R1, the A-DIFF terminal is connected to one end of resistor R3, and the A-COM terminal is connected to one end of resistor R7. The reverse connection protection unit is a D1 diode, whose anode is connected to the other end of the R7 resistor, and whose cathode is connected to a common node formed by the other end of the R1 resistor, the other end of the R3 resistor, and the ANODE terminal of the isolation unit, in order to prevent device damage caused by reverse connection when single-ended input is used. The filtering unit is connected between the common node and the signal shaping unit, as well as in the power supply circuit, and is used to perform noise filtering on the input signal and the power supply signal. The isolation unit is an OC1 isolation device, with its ANODE terminal connected to the common node, its VE terminal connected to VCC_3V3, its VO terminal connected to the input terminal of the signal shaping unit, and its GND terminal connected to GND, which is used to achieve electrical isolation between the input terminal and the control terminal. The signal shaping unit is a U1 Schmitt trigger, whose input is connected to the VO terminal of the isolation unit, the power supply is connected to VCC_3V3, the ground terminal is connected to GND, and the output is connected to the GPIO port of the main control MCU. It is used to shape the isolated signal into a standard square wave signal. The main control MCU receives the square wave signal output by the signal shaping unit through the GPIO port; By switching the wiring method of the input terminal group, a single-ended input mode can be achieved, where the A-24V terminal is connected to the resistor R1 and the A-COM terminal is connected to the resistor R7 and the diode D1, or a differential input mode can be achieved, where the A-DIFF terminal is connected to the resistor R3 and the A-COM terminal is connected to the resistor R7 and the diode D1.

2. The circuit for implementing differential and single-ended multiplexing of PLC input ports according to claim 1, characterized in that, The filtering unit includes capacitors C3, C4, C1, and C2. One end of capacitor C3 is connected to the common node, and the other end is connected to GND. One end of capacitor C4 is connected to the input terminal of the signal shaping unit, and the other end is connected to GND. Capacitor C1 is connected in parallel between the power supply terminal of the U1 Schmitt trigger and GND. Capacitor C2 is connected in parallel between the VE terminal of the OC1 isolation device and GND.

3. The circuit for implementing differential and single-ended multiplexing of PLC input ports according to claim 1, characterized in that, A resistor R4 is also connected between the VO terminal of the isolation unit and the input terminal of the signal shaping unit.

4. The circuit for implementing differential and single-ended multiplexing of PLC input ports according to claim 3, characterized in that, The R4 resistor has a parameter of 10-5%, and an R5 resistor with a parameter of 100-1% is also connected between the output of the signal shaping unit and the GPIO port of the main control MCU.

5. A circuit for implementing differential and single-ended multiplexing of PLC input ports according to claim 1, characterized in that, It also includes an indicator unit, which includes a D2 light-emitting diode and an R8 resistor. The cathode of the D2 light-emitting diode is connected to the output terminal of the U1 Schmitt trigger, and the anode is connected to GND through the R8 resistor.

6. A circuit for implementing differential and single-ended multiplexing of PLC input ports according to claim 1, characterized in that, The type of diode D1 is 1N4148W.

7. A circuit for implementing differential and single-ended multiplexing of PLC input ports according to claim 1, characterized in that, The OC1 isolation device is model NSI7211-DSPR.

8. A circuit for implementing differential and single-ended multiplexing of PLC input ports according to claim 1, characterized in that, The U1 Schmitt trigger of the signal shaping unit is model 74HC14PW.

9. A circuit for implementing differential and single-ended multiplexing of PLC input ports according to claim 1, characterized in that, The R1 resistor has a parameter of 3.3K-1%, the R3 resistor has a parameter of 150R-5%, and the R7 resistor has a parameter of 150R-5%.

10. A circuit for implementing differential and single-ended multiplexing of PLC input ports according to claim 1, characterized in that, In the single-ended input mode, the input single-ended input signal voltage is DC24V; in the differential input mode, the input differential input signal voltage is 5V.

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