Multi-path pulse width modulation signal transmission method for realizing long-distance transmission based on differential signals

Abstract

The invention discloses a multi-path pulse width modulation signal transmission method for realizing long-distance transmission based on differential signals, which comprises the following steps: S1, signal generation and differential conversion, S2, long-distance multi-path parallel transmission, S3, differential signal receiving and reduction, and S4, load driving. In this way, the lamp or the lamp strip can be designed and installed in a multi-section modular mode, an original scheme which can only be designed integrally is changed into a scheme which can be designed in a modular mode, the situation that the brightness is inconsistent due to the length problem can be solved, and the situation that the whole system goes wrong possibly due to the fault of a certain power source is avoided. And long-distance connection and cascading functions of the PWM signal, the SPI signal and the driving circuit are realized, so that the problem that the same path of PWM signal and SPI signal are used for driving lamps in different areas in the prior art is solved, and the brightness or color adjustment and control functions of the lamps are realized.

Description

Technical Field

[0001] This invention belongs to the field of lighting control technology, specifically relating to a method for transmitting multi-path pulse width modulation signals over long distances based on differential signals. Background Technology

[0002] In modern lighting control, industrial automation control and other fields, pulse width modulation (PWM) signals have become the core control signal for stepless load regulation due to their advantages such as high control precision, low hardware implementation cost and fast response speed. Especially in the field of LED lighting, the brightness adjustment and color temperature switching of almost all mid-to-high-end LED light strips and spotlights rely on PWM signals. With the acceleration of urbanization and the popularization of large-scale commercial and cultural tourism projects, the application scenarios of PWM control systems have put forward the core requirements of "large range, multi-zone, and high precision". Typical scenarios include whole-floor lighting of commercial complexes, facade outline lighting of super high-rise buildings, stage lighting for large-scale outdoor cultural tourism performances, and multi-area equipment indicator light groups in industrial parks. In such scenarios, the distance between the PWM controller and the load often reaches tens of meters or even hundreds of meters, and multiple independent loads need to be controlled simultaneously to achieve differentiated regulation.

[0003] Existing traditional PWM signals generally adopt a single-ended transmission architecture, that is, a transmission loop is formed by a single signal line and a common ground line. This architecture can work stably in short-distance (usually ≤5 meters) scenarios, but in long-distance transmission scenarios, there are two major technical bottlenecks that seriously restrict its application expansion. First, the signal attenuation is significant: during single-ended signal transmission, the voltage decreases linearly with the transmission distance. When the transmission distance exceeds 10 meters, the high-level amplitude of the PWM signal can decrease by more than 30%, resulting in duty cycle distortion. Specifically, this manifests as LED strip brightness shift, flickering, and inconsistent brightness of strips at different locations, which reduces the control accuracy of industrial equipment. Second, the anti-interference capability is weak: single-ended transmission has no noise suppression mechanism. In industrial sites and outdoor environments, electromagnetic interference generated by equipment such as frequency converters, motors, and high-voltage lines can easily couple to the signal line, forming noise and further damaging the integrity of the PWM signal. In extreme cases, this can lead to load loss of control. Summary of the Invention

[0004] The purpose of this invention is to provide a method for transmitting multi-path pulse width modulation signals over long distances based on differential signals, so as to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for transmitting multi-channel pulse width modulation signals over long distances based on differential signals, comprising the following steps: S1. Signal generation and differential conversion: Multiple independent single-ended signals are generated by the signal generation unit at the transmitting end. The signals are at least one of PWM single-ended signals, single-wire SPI single-ended signals, dual-wire synchronous SPI single-ended signals, or four-wire bidirectional synchronous SPI single-ended signals. Each single-ended signal is converted into a pair of differential signals with the same amplitude and opposite phase by the differential conversion unit. Each single-ended signal corresponds to a set of differential signal pairs. S2. Long-distance parallel transmission of multiple differential signals: The multiple differential signal pairs are respectively connected to multiple pairs of differential lines in the transmission medium, and the long-distance parallel transmission of multiple differential signals is realized through the transmission medium. During the transmission process, the signal reflection is eliminated through the impedance matching mechanism. S3. Differential signal reception and restoration: The receiving end receives each differential signal pair through the differential receiving unit, suppresses common-mode noise and extracts the differential signal through differential amplification, and then restores the differential signal to a PWM single-ended signal, single-wire SPI single-ended signal, dual-wire synchronous SPI single-ended signal or four-wire bidirectional synchronous SPI single-ended signal with the same parameters as the transmitting end through the signal restoration unit. After restoration, high-frequency noise is filtered out by the filtering unit. S4, Load Drive: The restored multiple single-ended signals are input to the corresponding load drive modules to drive the load to work. It also supports modular cascading expansion of multiple receivers. Through isolation measures, the failure of a single module can ensure that the operation of the overall system is not affected.

[0006] Preferably, in step S1, the transmitting end further includes an impedance matching unit. The PWM signal generation unit adopts a microcontroller (MCU), which can independently adjust the frequency of each PWM single-ended signal from 50Hz to 400Hz and the duty cycle from 0% to 100%. The core hardware and adjustable range of the transmitting end are clearly defined, enabling personalized adjustment of PWM signal parameters to adapt to different load requirements. It can also synchronously output single-wire SPI, dual-wire synchronous SPI, and four-wire bidirectional synchronous SPI signals and match the corresponding transmission timing.

[0007] Preferably, the differential conversion unit adopts a multi-channel differential transmitter or a combination of multiple single-channel differential transmitters, and the impedance matching unit is a 120-ohm precision terminating resistor connected across the output of the differential conversion unit to match the differential impedance of the differential line. The differential conversion hardware model and parameters are specified, and signal reflection is further eliminated through precise impedance matching to ensure the impedance consistency of the transmission link.

[0008] Preferably, in step S2, the transmission medium is a general-purpose Category 5e or Category 6 network cable. The network cable contains 4 pairs of differential lines, which can simultaneously transmit 4 PWM differential signals, or simultaneously transmit 4 single-wire SPI differential signals, or simultaneously transmit 2 dual-wire synchronous SPI differential signals, or simultaneously transmit 1 four-wire bidirectional synchronous SPI differential signal. Each signal occupies 1 pair of differential lines, and the four-wire bidirectional synchronous SPI signal occupies 4 pairs of differential lines.

[0009] Preferably, in step S3, the differential receiving unit at the receiving end adopts a multi-channel differential receiver that matches the model of the differential transmitter at the transmitting end. The filtering unit is an RC low-pass filter circuit. The transmitting end and the receiving end adopt a common ground design to ensure that the potentials of the transmitting and receiving ends are consistent, further improving the signal transmission stability. It consists of a 1k ohm resistor and a 0.1μF capacitor, with a cutoff frequency of 1.59kHz. It adopts adapted hardware and a common ground design, and accurately filters out high-frequency noise through RC low-pass filtering to enhance the signal transmission stability.

[0010] Preferably, in step S4, the load drive module adopts a DC step-down module, which can be replaced with other compatible drive modules according to actual needs, and can adapt to the needs of driving various loads with PWM signals and SPI signals.

[0011] Preferably, in step S4, the number of transmitted signals can be adjusted based on the number of differential line pairs in the transmission medium. By increasing or decreasing the number of differential conversion units, differential receiving units, and load drive modules, the corresponding number of connection ports can be matched to achieve the transmission of 1, 2, 3, 4, or more PWM signals.

[0012] Preferably, in step S4, the load includes, but is not limited to, LED light strips, industrial equipment indicator light groups, and servo motors, adapting to various PWM control scenarios such as lighting control and industrial equipment control. The adaptable load types and application scenarios broaden the applicability of this transmission method.

[0013] Preferably, in S1, each single-wire SPI single-ended signal corresponds to one set of differential signal pairs. In S3, the restored single-wire SPI signal retains the original data transmission timing, enabling cascading of SPI slave devices with multiple receivers. Each SPI slave is controlled by an independent chip select signal, and each SPI signal is transmitted through an independent differential transmitter, differential line, and differential receiver, sharing the same grounding loop. This ensures the independence and stability of long-distance transmission of the single-wire SPI signal, while also enabling collaborative control of multiple slaves without interference.

[0014] Preferably, in S1, the dual-wire synchronous SPI single-ended signal includes a CLK clock signal and a MOSI data signal, each corresponding to one set of differential signal pairs, occupying a total of two pairs of differential lines, ensuring that the clock and data of the dual-wire synchronous SPI signal are transmitted synchronously. The four-wire bidirectional synchronous SPI single-ended signal includes a CLK clock signal, a MOSI data transmit signal, a MISO data receive signal, and a CS chip select signal, each corresponding to one set of differential signal pairs, occupying a total of four pairs of differential lines on the network cable, realizing the independent transmission of the four-wire bidirectional SPI signal across the entire link, and ensuring the stability and accuracy of bidirectional data interaction.

[0015] Compared with the prior art, the beneficial effects of the present invention are: (1) By implementing multi-segment cascading and long-distance transmission of PWM signals and SPI signals, lamps or light strips can be designed and installed in multi-segment modular form, transforming the original integrated design into a modular design. This solves the problem of inconsistent brightness caused by length issues and avoids the possibility of a power supply failure causing problems for the entire system. Furthermore, since the long-distance connection and cascading function of PWM signals, SPI signals and driving circuits is realized, the previously unsolvable problem of using the same PWM signal and SPI signal to drive lamps in multiple different areas is solved, enabling lamp brightness or color adjustment and control functions.

[0016] (2) By leveraging the common-mode rejection characteristics of differential transmission, this invention can effectively resist electromagnetic interference generated by equipment such as frequency converters, motors, and high-voltage lines in industrial settings, avoid damage to PWM signals by noise, and ensure the integrity of the signal in complex electromagnetic environments. At the same time, the impedance matching design and the low attenuation characteristics of differential signals solve the signal distortion problem of traditional single-ended transmission, ensuring that the load is always in a stable working state without brightness drift, flickering, or control lag. The global common ground design further eliminates potential difference interference, ensures the synchronization of the entire link signal, improves the overall stability and reliability of the system, and extends the service life of the equipment.

[0017] (3) By using network cables to remotely transmit PWM signals, one network cable can realize up to 4 PWM transmissions, or 4 single-wire SPI transmissions, or 2 dual-wire SPI transmissions, saving application costs, facilitating installation, and providing a more stable and reliable solution for the system.

[0018] (4) Through the precise conversion and restoration of differential signals, the present invention can maintain the frequency and duty cycle parameters of the PWM signal without distortion, ensure the consistency of multi-zone load control accuracy, realize the coordinated adjustment of parameters such as brightness and color temperature, avoid the problems of asynchronous zone control and accuracy deviation in traditional solutions, and the mode of unified control of multiple loads by a single transmitter facilitates the realization of global collaborative control logic, simplifies control program design, and improves the overall control efficiency and experience of the system. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the 4-channel PWM transmission method of the present invention; Figure 2 This is a schematic diagram of the 4-channel single-wire SPI transmission method of the present invention; Figure 3 This is a schematic diagram of the two-way dual-wire synchronous SPI transmission method of the present invention; Figure 4 This is a schematic diagram of the single-channel four-wire bidirectional synchronous SPI transmission of the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed," "equipped with," "sleeved with," "connected," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0022] Please see Figures 1 to 4 The present invention provides a technical solution: Example:

[0023] 1. Hardware Selection 1.1 Hardware selection and details for the transmitting end: MCU: The system uses an STM32F103C8T6 minimum system board with a core frequency of 72MHz. It features four general-purpose timers (TIM1-TIM4) capable of outputting independent PWM signals. TIM2-TIM5 are selected to correspond to the four PWM outputs, with pin assignments as PA0 (TIM2_CH1), PA1 (TIM3_CH1), PA2 (TIM4_CH1), and PA3 (TIM5_CH1). It supports push-pull output mode, outputting a high level of 3.3V and a low level of 0V, meeting the input signal requirements of a differential transmitter. Additionally, this MCU includes SPI1 and S... The PI2 has two hardware SPI interfaces. SPI1 (PA5=SCK, PA6=MISO, PA7=MOSI, PA4=CS) is used to output a two-wire synchronous SPI signal. SPI2 (PB13=SCK, PB14=MISO, PB15=MOSI, PB12=CS) can be switched to single-wire SPI or four-wire bidirectional synchronous SPI mode. The pin output level is consistent with the PWM signal, which is compatible with the input requirements of differential transmitters. The minimum system board requires an external 5V power supply and is equipped with an 11.0592MHz crystal oscillator to ensure clock accuracy and avoid PWM frequency deviation.

[0024] 2. Differential Transmitter: The SN75176 differential bus transceiver is selected. This chip supports half-duplex communication, operates at a voltage of 4.75V~5.25V, and can be adapted to the 3.3V PWM signal output by the MCU. Six SN75176 chips are selected, with four chips corresponding to four PWM signals and two chips corresponding to one dual-wire synchronous SPI signal (SCK and MOSI each occupy one chip, MISO and CS can be multiplexed or configured separately. In this embodiment, MISO is used for signal feedback and CS is used for chip select control. One chip of each is added, for a total of four chips corresponding to one dual-wire synchronous SPI). The DI pin (data input terminal) of each chip is connected to one PWM output pin of the MCU. The DE pin (enable terminal) and RE pin (receive enable terminal) are connected to a high level of 5V to keep the chip in transmit mode.

[0025] 3. Impedance Matching Unit: A 120Ω±1% precision metal film resistor is selected. One resistor is connected in parallel for each differential signal, bridging pin A (differential positive output) and pin B (differential negative output) of the SN75176 chip. This is used to match the 120Ω characteristic impedance of the network cable differential pair and suppress signal reflection. The resistor should be placed close to the transmitter output interface to minimize the impact of lead length on impedance matching.

[0026] 4. Auxiliary circuit: A 1kΩ current-limiting resistor is connected in series between the MCU and SN75176 to prevent damage from excessive input current; a 0.1μF ceramic capacitor and a 10μF electrolytic capacitor are connected in parallel to the power supply pin (VCC) of the SN75176 chip to filter out power supply ripple and ensure stable chip operation.

[0027] 5. Transmission media selection and cabling requirements: Cable: Cat5e unshielded network cable (CAT5E) is used, with oxygen-free copper core material, 0.51mm diameter, 12-15mm twist pitch per differential pair, characteristic impedance 120Ω±15%, supporting a maximum transmission distance of 100 meters, meeting the 100-meter transmission requirements of this invention. The network cable contains 4 pairs of differential wires. This embodiment uses a hybrid transmission mode: 2 pairs of differential wires are used to transmit 2 PWM signals, and 2 pairs of differential wires are used to transmit 1 dual-wire synchronous SPI signal (SCK and MOSI each occupy 1 pair, MISO and CS multiplex 1 pair, or 4 pairs of network cables can be used separately to transmit 1 four-wire bidirectional synchronous SPI signal); if transmitting 4 single-wire SPI signals separately, the 4 pairs of differential wires can be assigned to 4 single-wire SPI signals respectively, with each signal occupying 1 pair. The color assignments are: PWM1 (white-orange-orange), PWM2 (white-green-green), SPI_SCK (white-blue-blue), SPI_MOSI (white-brown-brown).

[0028] 6. Cabling Specifications: Network cables must be laid separately, avoiding parallel laying with high-voltage power lines (220V and above). If crossing, they must be perpendicular to each other at 90° with a spacing of no less than 30cm. During the cabling process, avoid excessive bending (bending radius ≥ 8 times the wire diameter), twisting, and stretching to ensure that the differential wire twist pitch is not damaged. The connectors at both ends should be RJ45 crystal heads, using the T568B standard crimping to ensure accurate wire pair correspondence, no misconnections or loose connections, and ensure synchronous transmission of PWM and SPI signals.

[0029] 7. Receiver hardware selection and details: Differential Receiver: Six SN75176 chips, identical to those used in the transmitter, are selected, each corresponding to one of the transmitters. Four chips receive four PWM signals, and two chips receive one dual-wire synchronous SPI signal (SCK, MOSI). If MISO or CS feedback / control is included, additional chips are added accordingly. The DE and RE pins of the chip are connected to a low level (0V) to put the chip in receive mode. Pins A and B are connected to the corresponding wire pairs of the RJ45 network cable connector to receive differential signals. The RO pin (data output) serves as the output terminal for the restored PWM and SPI signals, with output levels consistent with the transmitter MCU (3.3V / 0V). The SCK and MOSI output terminals of the SPI are connected to the corresponding pins of the receiver MCU or load control chip to achieve signal synchronization.

[0030] 8. RC Filtering Unit: Each PWM signal and SPI signal (SCK, MOSI, MISO, CS) is equipped with one RC low-pass filter circuit. The resistors are 1kΩ±1% metal film resistors, and the capacitors are 0.1μF±5% multilayer ceramic capacitors. The circuit topology is a series RC structure, i.e., the RO pin of the SN75176 is connected in series with a resistor, which is then connected to one end of the capacitor. The other end of the capacitor is grounded. The filtered signal is led out to the driver module from the connection point of the resistor and capacitor. The cutoff frequency of this circuit is f=1 / (2πRC)≈1.59kHz, which can effectively filter out high-frequency noise above 10kHz without affecting the PWM signal waveform from 50Hz to 400Hz.

[0031] 9. Auxiliary circuit: A 0.1μF ceramic capacitor and a 10μF electrolytic capacitor are also connected in parallel at the power supply terminal of the SN75176 chip; a 10kΩ pull-up resistor is connected in parallel at the output terminal of the filter circuit (especially the SCK and MOSI pins of SPI) to ensure a stable low level output when there is no signal and to avoid malfunction of the driver module.

[0032] 10. Load driver module and load selection: Driver Module: An XL6009 DC-DC step-down module (with PWM control) is selected, with 4 signals corresponding to 4 modules for driving loads such as LED strips. A new SPI signal driver module (using an STM32F103C8T6 minimum system board as the receiver control core) is added to receive the restored SPI signal, enabling load parameter configuration, status feedback, and multi-load collaborative control. The module's input voltage range is 12V~24V, and the output voltage is continuously adjustable from 3.3V to 12V, with a maximum output current of 3A and a maximum single-channel drive power of 36W (12V / 3A). The module's PWM control pin (usually labeled "PWM" or "ADJ") connects to the filtered signal received at the receiver, adjusting the output current through the PWM duty cycle to control the LED strip brightness. The module's enable pin (EN) is connected to a high level of 12V to maintain operation.

[0033] 11. Load: Use 5050 type RGB LED strip (single-channel white light), 60 LEDs per meter, rated voltage 12V, rated current 2A / meter, 2 meters per channel (total power 48W), and install aluminum heat sinks to prevent overheating damage. Connect the positive and negative terminals of the LED strip to the output positive and negative terminals of the XL6009 module respectively. Each channel of the LED strip is connected in series with a 5A fast-blow fuse to prevent short circuits from burning out the module.

[0034] 12. Power supply system: The control circuits (MCU, SN75176) of the transmitting and receiving ends are powered by a 12V to 5V / 3A switching power supply; the driver module and LED light strip are powered by a 12V / 10A switching power supply. The two power supplies are connected to the same ground to ensure that the potential of the transmitting and receiving ends is consistent and to avoid PWM / SPI signal distortion and SPI data errors.

[0035] 1.2 Implementation Steps 1. Hardware connection steps: Transmitter Assembly: First, fix the STM32F103C8T6 minimum system board onto the experimental board, and solder the power interface, crystal oscillator, and reset circuit. Insert four SN75176 chips into the slots on the experimental board, and solder the power pins and enable pins (DE / RE connected to 5V). Connect the PA0-PA3 pins of the MCU to the DI pins of the four SN75176 chips via 1kΩ resistors, and then solder them to the corresponding PA5-PA7 pins (SPI1_SCK, SPI1_MISO, SP...). After connecting the I1_MOSI and PA4 (SPI1_CS) pins in series with 1kΩ resistors, solder them to the DI pins of two (or four) other SN75176 chips. Connect a 120Ω terminating resistor in parallel between the A and B pins of each SN75176 chip, and then solder the A and B pins to the corresponding wire pairs of the RJ45 connector (according to the T568B standard). Finally, connect a 12V to 5V power supply to the MCU and SN75176, and test that the supply voltage is stable at 5.0V±0.1V.

[0036] 2. Transmission link setup: Cut a 100-meter Cat5e network cable, crimp RJ45 connectors at both ends according to the T568B standard, insert one end into the transmitting end's RJ45 interface, and connect the other end to the receiving end's RJ45 interface. Use a network cable tester to check that all 8 cores are connected and there is no crosstalk or short circuit.

[0037] 3. Receiver Assembly: Insert six SN75176 chips into the receiver experimental board, connecting the DE / RE pins to 0V; solder the corresponding RJ45 connector pins to the A and B pins of the SN75176 (4 for PWM and 2 for SPI); connect a 1kΩ resistor in series to the RO pin of each SN75176, then connect one end of a 0.1μF capacitor and one end of a 10kΩ pull-up resistor, grounding the other end of the capacitor and connecting the other end of the pull-up resistor to 3.3V. The filtered signal is then output to the PWM control pin of the XL6009 module; the filtered SPI signals (SCK, MOSI, MISO, CS) are output to the SPI interface of the receiver MCU; the receiver control circuit is connected to a 12V to 5V power supply, and the power supply is tested to be normal.

[0038] 4. Load and Driver Connection: Connect the four XL6009 modules to a 12V / 10A power supply, and adjust the module output to 12V. Connect a 2-meter 5050 LED strip to the output of each module after connecting a 5A fuse in series. Connect the filtered PWM signal to the corresponding PWM control pin of each module, ensuring that the wiring is free of reverse polarity or loose connections. Connect the three groups of industrial equipment indicator lights to the GPIO pins of the receiving MCU. Control each group of indicator lights through the SPI chip select signal (CS). Connect the SCK and MOSI pins of the SPI to the corresponding SPI interface of the receiving MCU to realize command transmission. Debug the SPI chip select function to ensure that each group of indicator lights can be controlled independently.

[0039] 5. Common grounding: Connect the GND pins of the transmitting and receiving control circuits to the GND pins of the driver module and LED strip power supply through a 1.5mm² copper wire to the same grounding busbar to achieve global common grounding and eliminate potential difference interference.

[0040] 6. Parameter configuration and program logic: MCU program development: Based on the Keil MDK5 development environment, STM32 standard library programming is used. The core logic includes timer initialization, PWM output configuration, and duty cycle adjustment. The timer is configured as PWM mode 1, the clock source is the internal 72MHz crystal oscillator, the frequency divider is 720, and the counter auto-reload value is 999. The calculated PWM frequency is 72MHz / (720×1000)=100Hz, which meets the design requirements.

[0041] 7. Duty cycle configuration: The duty cycle of the four PWM signals is set to 30%, 50%, 70%, and 90% respectively through the program, and the corresponding timer compare register values ​​are 300, 500, 700, and 900 respectively; an infinite loop is added to the program to maintain a stable output of the duty cycle, and a serial port debugging interface is reserved so that the duty cycle can be read and modified in real time through the host computer.

[0042] 8. Program Download and Debugging: Write the compiled program to the MCU using the SWD downloader. After startup, use an oscilloscope to measure the output of the MCU's PA0-PA3 pins to confirm that the PWM waveform is normal, with a frequency of 100Hz±1Hz, a duty cycle deviation of ≤0.5%, a high level of 3.3V±0.1V, and that the SPI signal timing is normal (clock frequency of 500kHz±10kHz, no data transmission distortion). Measure the filtered PWM and SPI signals at the receiving end to ensure they are consistent with those at the transmitting end, ensuring that the signal restoration is distortion-free.

[0043] 9. System Testing and Result Verification: Basic performance test: After the system is started, all four LED strips are observed to light up normally, with brightness levels of 30%, 50%, 70%, and 90% respectively, without flickering or brightness transition delay; the PWM and SPI signals after filtering at the receiving end are measured with an oscilloscope, and the waveforms are without distortion, with the frequency and duty cycle consistent with the transmitting end, and the distortion is ≤0.5%; after 72 hours of continuous operation, the LED strip brightness is stable, and there is no module overheating or signal loss.

[0044] 10. Long-distance transmission accuracy test: Illuminance was measured at the midpoint of each light strip using a lux meter. 30% duty cycle corresponds to 120 lux ± 3 lux, 50% corresponds to 200 lux ± 4 lux, 70% corresponds to 280 lux ± 5 lux, and 90% corresponds to 360 lux ± 6 lux. The brightness deviation was ≤1.5%, which is far superior to traditional single-ended transmission (deviation ≥8%). The signal attenuation after 100 meters of transmission was measured with an oscilloscope. The high-level amplitude attenuation was ≤5%, which is far lower than the attenuation of more than 30% in single-ended transmission.

[0045] 11. Anti-interference performance test: Place a 1.5kW frequency converter near the receiving end, 1 meter away from the experimental board at the receiving end. After starting the frequency converter, observe that the brightness of the LED strip does not change, and measure the PWM and SPI waveforms with an oscilloscope and find that there is no noise superposition. The common mode noise rejection ratio is ≥40dB and the differential mode noise rejection ratio is ≥35dB, which meets the requirements of the electromagnetic environment in the industrial site.

[0046] 12. Reliability and scalability test: When the power supply of the second driver module is disconnected, the other three light strips still work normally without mutual interference; when the fifth and sixth extended signals are connected (using spare wire pairs of the network cable, and adding corresponding SN75176 chips and driver modules), the brightness of the extended channels is stable after startup, realizing flexible capacity expansion; when the network cable is slightly bent and pulled (bending radius 10cm, pulling force ≤5kg), the signal transmission is uninterrupted and the brightness of the light strips remains unchanged.

[0047] 13. Test Conclusion: This embodiment achieves stable transmission of 4 PWM signals and 1 dual-wire synchronous SPI signal (expandable to 4 single-wire SPI or 1 four-wire bidirectional SPI) over a long distance of 100 meters. The PWM control accuracy, SPI data transmission reliability, and anti-interference performance meet the requirements of large-scale lighting control and industrial equipment collaborative control scenarios, and support modular expansion, which is in line with the design goals of this invention.

[0048] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for transmitting multi-channel pulse width modulation signals over long distances based on differential signals, characterized in that, Includes the following steps: S1. Signal generation and differential conversion: Multiple independent single-ended signals are generated by the signal generation unit at the transmitting end. The signals are at least one of PWM single-ended signals, single-wire SPI single-ended signals, dual-wire synchronous SPI single-ended signals, or four-wire bidirectional synchronous SPI single-ended signals. Each single-ended signal is converted into a pair of differential signals with the same amplitude and opposite phase by the differential conversion unit. Each single-ended signal corresponds to a set of differential signal pairs. S2. Long-distance parallel transmission of multiple differential signals: The multiple differential signal pairs are respectively connected to multiple pairs of differential lines in the transmission medium, and the long-distance parallel transmission of multiple differential signals is realized through the transmission medium. During the transmission process, the signal reflection is eliminated through the impedance matching mechanism. S3. Differential signal reception and restoration: The receiving end receives each differential signal pair through the differential receiving unit, suppresses common-mode noise and extracts the differential signal through differential amplification, and then restores the differential signal to a PWM single-ended signal, single-wire SPI single-ended signal, dual-wire synchronous SPI single-ended signal or four-wire bidirectional synchronous SPI single-ended signal with the same parameters as the transmitting end through the signal restoration unit. After restoration, high-frequency noise is filtered out by the filtering unit. S4, Load Drive: The restored multiple single-ended signals are input to the corresponding load drive modules to drive the load to work. It also supports modular cascading expansion of multiple receivers. Through isolation measures, the failure of a single module can ensure that the operation of the overall system is not affected.

2. The method for transmitting multi-channel pulse width modulation signals over long distances based on differential signals according to claim 1, characterized in that: In S1, the transmitting end also includes an impedance matching unit. The signal generation unit adopts a microcontroller, which can independently adjust the frequency of each PWM single-ended signal, and can synchronously output single-wire SPI, dual-wire synchronous SPI, and four-wire bidirectional synchronous SPI signals and match the corresponding transmission timing.

3. The method for transmitting multi-channel pulse width modulation signals over long distances based on differential signals according to claim 1, characterized in that: The differential conversion unit employs a multi-channel differential transmitter or a combination of multiple single-channel differential transmitters. The impedance matching unit is a 120-ohm precision terminating resistor connected across the output of the differential conversion unit to match the differential impedance of the differential lines.

4. The method for transmitting multi-channel pulse width modulation signals over long distances based on differential signals according to claim 1, characterized in that: In S2, the transmission medium is a general-purpose Category 5e or Category 6 network cable. The network cable contains 4 pairs of differential lines, which can transmit 4 PWM differential signals, or 4 single-wire SPI differential signals, or 2 dual-wire synchronous SPI differential signals, or 1 four-wire bidirectional synchronous SPI differential signal simultaneously. Each signal occupies 1 pair of differential lines, and the four-wire bidirectional synchronous SPI signal occupies 4 pairs of differential lines.

5. The method for transmitting multi-channel pulse width modulation signals over long distances based on differential signals according to claim 1, characterized in that: In S3, the differential receiving unit of the receiving end adopts a multi-channel differential receiver that matches the model of the differential transmitter of the transmitting end, the filtering unit is an RC low-pass filter circuit, and the transmitting end and the receiving end adopt a common ground design to ensure that the potential of the transmitting and receiving ends is consistent, thereby further improving the signal transmission stability.

6. The method for transmitting multi-channel pulse width modulation signals over long distances based on differential signals according to claim 1, characterized in that: In S4, the load drive module adopts a DC step-down module.

7. The method for transmitting multi-channel pulse width modulation signals over long distances based on differential signals according to claim 1, characterized in that: In S4, the number of transmitted signals can be adjusted based on the number of differential line pairs in the transmission medium. By increasing or decreasing the number of differential conversion units, differential receiving units, and load drive modules to match the corresponding number of connection ports, the transmission of 1, 2, 3, 4, or more PWM signals can be achieved.

8. The method for transmitting multi-channel pulse width modulation signals over long distances based on differential signals according to claim 1, characterized in that: In S4, the load includes, but is not limited to, LED light strips, industrial equipment indicator light groups, and servo motors, adapting to PWM control scenarios for lighting control and industrial equipment control.

9. The method for transmitting multi-channel pulse width modulation signals over long distances based on differential signals according to claim 1, characterized in that: In S1, each single-wire SPI single-ended signal corresponds to one set of differential signal pairs. In S3, the restored single-wire SPI signal retains the original data transmission timing, enabling cascading of SPI slave devices with multiple receiving ends. Each SPI slave is controlled by an independent chip select signal, so they do not interfere with each other. Each SPI signal is transmitted through an independent differential transmitter, differential line, and differential receiver, sharing the same grounding loop.

10. The method for transmitting multi-channel pulse width modulation signals over long distances based on differential signals according to claim 1, characterized in that: In S1, the dual-wire synchronous SPI single-ended signal includes the CLK clock signal and the MOSI data signal, each corresponding to one set of differential signal pairs, occupying a total of two pairs of differential lines. The four-wire bidirectional synchronous SPI single-ended signal includes the CLK clock signal, the MOSI data transmission signal, the MISO data reception signal, and the CS chip select signal, each corresponding to one set of differential signal pairs, occupying a total of four pairs of differential lines on the network cable.

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