A visible light communication system based on intensity modulation direct detection

Abstract

The present invention discloses a visible light communication system based on intensity modulation direct detection, belonging to the technical field of data transmission. The system of the present invention is composed of a power supply part, a transmitting part and a receiving part. First, the voltage stabilizing module stabilizes the input voltage to 12V and 15V respectively, and then the dual power module converts the single power supply into a dual power supply of ±5V, and supplies power to the receiving circuit and the bandpass filter to make it work normally; then the analog signal to be transmitted is directly loaded onto the white light LED, and the signal modulation is realized by changing the intensity of the light source. Finally, the PIN diode receives the signal and processes it, thereby realizing the transmission of audio signals and image information. The system selects the communication mode of intensity modulation direct detection, which is mainly composed of an input analog signal, an optical transmitter, an optical channel, and an optical receiver. Since this method does not require the use of complex modulation, demodulation circuits and external modulators, the system structure is simpler, the system failure points are reduced, and the adaptability is strong.

Description

Technical Field

[0001] The present invention relates to the technical field of data transmission, and in particular to a visible light communication system based on intensity modulation direct detection. Background Art

[0002] With the development of emerging information industries and the continuous evolution of mobile Internet, human society is moving towards a digital intelligent era characterized by "everything is sensed, everything is connected, and everything is intelligent", which puts forward higher requirements for high-speed and low-latency information interaction, but radio frequency spectrum resources cannot meet this demand. Unlike radio frequency communication, which requires spectrum allocation, the frequency band used by visible light communication (VLC) belongs to white spectrum and can be used without authorization. It uses visible light bands for information transmission and has the advantages of high transmission rate, good security, and rich spectrum resources. It is known as a green communication technology for the future and has shown great application potential in smart homes, smart cities and other fields.

[0003] However, despite the many advantages of VLC technology, it still has some obvious technical disadvantages in practical applications. Among them, one of the most prominent problems is the high cost. Traditional VLC systems usually use complex devices and expensive equipment, resulting in high overall costs and difficulty in large-scale promotion and application. In addition, the productivity of VLC systems is also subject to certain limitations, especially in high-speed communications, system stability and reliability are often difficult to guarantee.

[0004] In view of the above problems, the present invention designs a visible light communication system based on intensity modulation direct detection. The system can transmit audio signals and image information while in normal lighting, providing new spectrum resources for wireless communication. Moreover, since visible light propagation is not easily interfered with or restricted, the system has better information transmission security performance. By precisely controlling the intensity of the optical signal, efficient information transmission is achieved. At the same time, direct detection technology also greatly simplifies the structure of the receiving end, reduces system costs, and provides new possibilities for the promotion and application of VLC technology. Summary of the invention

[0005] The purpose of the present invention is to provide a visible light communication system based on intensity modulation direct detection in order to solve the above-mentioned problem.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is: including selecting the IM / DD communication mode, characterized in that: the two main parts of the transmitting part and the receiving part are analyzed by analyzing the characteristics of the transmission signal and designing the corresponding basic architecture, wherein:

[0007] (1) The emission part is a light driving circuit, which drives the LED through a high-power transistor to transmit signals while lighting. The circuit selects the emitter bias circuit, which can effectively avoid the influence of the transistor current amplification factor, base-emitter voltage and other parameters on the static operating point due to temperature changes.

[0008] (2) The receiving part consists of a transimpedance amplifier and an amplitude amplifier. The transimpedance amplifier selects the photovoltaic mode, converts the current into voltage, and measures the tiny electrical signal. The amplitude amplifier amplifies the amplitude and finally transmits the analog signal to the peripheral device.

[0009] Furthermore, signal transmission is divided into audio signal and image signal, among which,

[0010] The audio signal passes through the optical driving circuit, which enables the LED to complete the normal lighting function and convert the electrical signal into an optical signal. The photodetector then converts the detected optical signal into an electrical signal, which is convenient for the system to process and amplify the amplitude. The amplified analog signal is then transmitted to the bandpass filter to filter out an audio signal and compare the audio signal before and after passing through the filter.

[0011] The image signal generates image information through an analog camera, passes through an optical drive circuit, drives the LED lighting and transmits the image information, performs electro-optical conversion, and then the photodetector converts the detected tiny signal into an electrical signal, amplifies the signal amplitude, and then transmits the amplified signal to the video recorder, and finally displays the image information on the screen.

[0012] Furthermore, the LED selected the 12V 3W Purui lamp beads with high light efficiency and high color rendering.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] (1) By controlling the high-speed flashing of light-emitting diodes to transmit information, VLC has an ultra-wide spectrum band (430 THz), which can greatly expand the available bandwidth resources and break through the spectrum resource bottleneck faced by future communication networks.

[0015] (2) Visible light communication can optimize the lighting environment, provide higher brightness and softer light effects, and improve people's quality of life. At the same time, it fully utilizes the advantages of light-emitting diodes as a new type of energy-saving light source, realizes the organic combination of lighting, intelligent control and intelligent communication, and opens up a new situation for the application of the Internet of Things.

[0016] (3) The system selects the communication mode of intensity modulation direct detection, which is mainly composed of input analog signal, optical transmitter, optical channel and optical receiver. Since this method does not require the use of complex modulation and demodulation circuits and external modulators, the system structure is simpler, the system failure points are reduced, and the adaptability is strong; and the required components and circuits are fewer, with lower implementation costs and faster response speeds, and it can adapt to high-speed data transmission and is more competitive in the market.

[0017] (4) The IM / DD method adopted by the present invention has the advantages of simple structure and low power consumption, and is very suitable for short-distance high-speed communication scenarios.

[0018] (5) This system has good compatibility and scalability, and can be combined with other wireless communication technologies to form a more complete communication network. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a basic framework diagram of the audio signal transmission system of the present invention;

[0020] Figure 2 is a schematic diagram of a transmitting circuit of the present invention;

[0021] Figure 3 The TIA photoelectric detection circuit of the present invention;

[0022] Figure 4 The inverting amplitude amplification circuit diagram of the present invention;

[0023] Figure 5 The bandpass filter circuit diagram of the present invention;

[0024] Figure 6 It is a basic framework diagram of the image information transmission system of the present invention;

[0025] Figure 7 The same-phase amplitude amplification circuit diagram of the present invention;

[0026] Figure 8 Schematic diagram of spectrum resources of the present invention

[0027] Fig. 9 is a block diagram of the IM-DD system of the present invention;

[0028] Fig.10 The schematic diagram of the transmitting circuit after debugging of the present invention;

[0029] Fig.11 It is a schematic diagram of a receiving circuit of the present invention;

[0030] Fig.12 is an input audio signal result diagram of the present invention;

[0031] Fig.13The result diagram of the audio signal after filtering of the present invention;

[0032] Fig.14 This is the first version of the image information transmission test chart of the present invention;

[0033] Fig.15 This is the second version of the image information transmission test chart of the present invention;

[0034] Fig.16 It is the overall structural block diagram of the present invention. DETAILED DESCRIPTION

[0035] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further explained below in conjunction with specific implementation methods.

[0036] like Fig.16 As shown, the upper part is the audio signal transmission system, and the lower part is the image information transmission system. Connect the two power supply ends together, and use the key switch to select one of the systems to power. This system consists of a power supply part, a transmitting part, and a receiving part. First, the voltage regulator module stabilizes the input voltage to 12V and 15V respectively, and then the dual power module converts the single power supply into a dual power supply of ±5V to power the receiving circuit and the bandpass filter to make it work normally; finally, the white light LED illuminates the PIN diode to transmit audio signals and image information.

[0037] In order to make the system structure simpler and reduce the implementation cost, the present invention can adapt to high-speed data transmission and different application scenarios and light sources. The system selects the IM / DD communication mode. The analog signal to be transmitted is directly loaded onto the white light LED, and the signal modulation is achieved by changing the intensity of the light source, wherein the LED is both a light source and a modulator. Direct detection does not undergo any transformation, and a photodetector (PIN or APD) is used to directly detect the optical signal and convert it into an electrical signal. This signal is generally very weak and needs to be amplified.

[0038] This system is mainly composed of two parts: the transmitting part and the receiving part. The corresponding basic architecture is designed by analyzing the characteristics of the transmission signal.

[0039] (1) The emission part is a light driving circuit, which drives the LED through a high-power transistor to transmit signals while lighting. The circuit selects the emitter bias circuit, which can effectively avoid the influence of the transistor current amplification factor, base-emitter voltage and other parameters on the static operating point due to temperature changes.

[0040] (2) The receiving part consists of a transimpedance amplifier and an amplitude amplifier. The transimpedance amplifier selects the photovoltaic mode, converts the current into voltage, and measures the tiny electrical signal, while the amplitude amplifier amplifies the amplitude. Finally, the analog signal is transmitted to peripherals such as speakers and display screens.

[0041] This system uses Hikvision's high-definition coaxial analog camera to transmit PAL analog video signals. The frame rate of PAL video signals is 25 frames per second, and each pixel consists of 3 components (red, green, and blue), each component is represented by 8 bits, that is, each pixel requires 24 bits to represent.

[0042] If T v is the time required to scan all pixels of an image, N H is the total number of horizontal pixels, N v is the total number of vertical pixels, then the duration of each pixel is calculated as:

[0043]

[0044] One complete cycle of the square wave of the maximum video frequency is equal to the duration of two adjacent pixels, so the maximum video frequency f max for:

[0045]

[0046] in is the vertical refresh rate.

[0047] Since the full cycle of the minimum video frequency contains only one pixel, the minimum video frequency f min Actually depends on the vertical refresh rate:

[0048]

[0049] The definition of the analog camera is standard 720P, so the effective resolution is 1280×720, and the total resolution is N H ×N v =1650×750, the vertical refresh rate is 60Hz, so from equations (2) and (3), we can know that

[0050] The maximum video frequency is:

[0051] The minimum video frequency is: f min =f v =60Hz.

[0052] Therefore, designing a visible light communication system to transmit PAL signals requires the selection of large-bandwidth devices and circuits.

[0053] Audio signal transmission system design:

[0054] like Figure 1 As shown, the audio signal passes through the optical driving circuit, enabling the LED to complete the normal lighting function and convert the electrical signal into an optical signal. The photodetector then converts the detected optical signal into an electrical signal, which is convenient for the system to process and amplify its amplitude. The amplified analog signal is then transmitted to the bandpass filter to filter out a section of audio signal, and the audio signal before and after passing through the filter is compared.

[0055] The transmitting circuit uses an emitter bias circuit to drive the white light LED lighting, which loads the signal into the light source and sends it out. Figure 2 As shown in the figure, first adjust the quiescent operating point Q of the transistor to make it in the amplification state; then input the audio signal, transmit the signal to the collector, and the bias current drives the LED lighting, converting the electrical signal into an optical signal, and modulating the intensity of the optical signal. This circuit has the characteristics of high gain, good stability, and strong anti-interference ability, and is widely used in audio equipment and radio equipment.

[0056] Generally, the forward voltage drop of a 3W LED is 3.4V to 3.8V, and the modulation depth of the LED is:

[0057]

[0058] Among them, I C is the collector current at the static operating point, I M is the peak current, and ΔI is the difference between the peak current and the bias current. The higher the modulation index, the easier it is to detect the optical signal, but too high a modulation index will reduce the bandwidth and affect the system performance.

[0059] In order to maximize the magnification of the transistor during operation, ideally:

[0060]

[0061] Among them, U CQ is the collector voltage of the transistor when it is in static operation, U CC is the power supply voltage.

[0062] Let U CC =12V,m=3%,β=12,U BEQ =0.7V,U LED =3.45V,I M =700mA

[0063] Then U CQ =6V. From formula (1), we can get I C =550mA.

[0064] Base current I B, collector current I C and emitter current I E Has the following relationship:

[0065]

[0066] So I E ≈I C =550mA,I B =42.3mA.

[0067] U CEQ ≈U CC -I CQ R3-U LED (7)

[0068] Among them, U CEQ is the voltage between the collector and the emitter, and R3 is the DC feedback resistor.

[0069] Let U CEQ =5V, then 6≈12-0.55R3-3.45, R3≈6.45V.

[0070] U BQ =U BEQ +R3I E (8)

[0071] Among them, U BQ is the base voltage during static operation. Because the transistor is a silicon tube, U BEQ =0.7V.

[0072] Then U BQ =U BEQ +R3I E =0.7+6.45×0.55=4.25V.

[0073] U BQ It can also be represented by bias resistors R1 and R2, that is, R1 and R2 divide the supply voltage:

[0074]

[0075] Let R2 = 47kΩ, then R1 = 85.7kΩ.

[0076] Welding was performed according to the calculated values ​​above. After debugging, it was found that when R1 = 5.6kΩ, R2 = 47kΩ, the transmitter can achieve normal lighting while transmitting signals.

[0077] The optical receiving circuit consists of a transimpedance amplifier and an amplitude amplifier. A transimpedance amplifier (TIA) is a converter that uses a single or multiple operational amplifiers to convert current into voltage. It is often used in conjunction with a photodiode to detect weak photocurrent signals. Since the signal received by the photodetector in this visible light communication system is relatively weak, the transimpedance amplifier selects the photovoltaic mode, such as Figure 3 shown.

[0078] Transimpedance amplifier circuit: C DIFF is the parasitic differential capacitance of the chip input, C CM is the parasitic common mode capacitance of the chip input, C D is the parasitic capacitance, then the total parasitic capacitance C of the front-end input S =C D +C CM +C DIFF When the PIN diode model is determined, C D is a fixed value.

[0079] Assuming that the op amp is ideal, the typical value of GBP of OPA8045 is 1GMHz, then the -3dB closed-loop bandwidth it can achieve is approximately:

[0080]

[0081] Where R f is the feedback resistor and GBP is the gain-bandwidth product of the op amp.

[0082] The gain of this transimpedance amplifier is:

[0083]

[0084] Among them U out is the output signal voltage, I PD is the reverse current flowing through the photodiode.

[0085] Let C S =10pF,R f =100kΩ, f0 = 1MHz, substituting into the variables we can get

[0086] -3dB closed-loop bandwidth:

[0087] Circuit magnification:

[0088] Since the parasitic capacitance and feedback resistance of the front end will form a zero point on the noise gain curve, the approach speed of the intersection of the open-loop gain curve and the noise gain curve of the operational amplifier is -40dB / dec, which causes self-excitation. In order to make the operational amplifier work stably, Cf As compensation:

[0089]

[0090] Among them, Q = 0.707 is the quality factor, f0 is the center frequency, so

[0091] The amplitude amplification circuit selects an inverting proportional amplifier to perform secondary amplitude amplification on the signal passing through the transimpedance amplifier. Figure 4 As shown, it has the characteristics of high input impedance, low noise factor and reverse voltage protection. This circuit makes the leakage of input signal very small, so as to better maintain the integrity of input signal. At the same time, the feedback circuit is used to reduce the noise factor, so that the noise factor of the circuit is very low, which can better maintain the accuracy of the signal.

[0092] The gain of the inverting amplifier circuit is:

[0093]

[0094] Among them, R f is the feedback resistor, R2 is the balancing resistor, R2=R1 / / R f .

[0095] Let the magnification be 10, R1 = 2kΩ, then R f =10kΩ, R2≈2kΩ.

[0096] Active bandpass filter: The circuit consists of an op amp, capacitors and resistors, such as Figure 5 As shown in the figure, it filters out a waveform of a certain frequency and filters out all signals below or above this frequency band. An ideal bandpass filter has a flat passband, in which signals are not amplified or attenuated, while signals outside this passband are completely attenuated.

[0097] In reality, the ideal situation does not exist. Signals outside the passband are attenuated but not completely isolated. This phenomenon is called the roll-off phenomenon of the bandpass filter. Therefore, when designing a bandpass filter, attention should be paid to the setting of the roll-off range. The narrower the roll-off range, the closer its performance is to the designed circuit.

[0098] The quality factor (Q) of a bandpass filter is a parameter that characterizes the quality of the resonant circuit. The larger the Q value, the better the selectivity of the resonant circuit and the narrower the passband. The calculation formula is:

[0099]

[0100] Where f0 is the center frequency of the circuit and BW is the passband.

[0101] Assume f0 = 600Hz, BW = 100, Au = 2, C = 10nF,

[0102] From formula (11), we can get the quality factor Q=6.

[0103]

[0104] Where R3 is the feedback resistor, then

[0105] The gain of this bandpass filter is:

[0106]

[0107] Because the magnification A u =2, R3=318kΩ, so R1=79.5kΩ.

[0108] The calculation formula for R2 is:

[0109]

[0110] Substituting in the variables we get:

[0111] The passband calculation formula of the bandpass filter is:

[0112]

[0113] Substituting in the variables we get: Meets design requirements.

[0114] Image information transmission system design:

[0115] like Figure 6 As shown, the system generates image information through an analog camera, drives the LED lighting and transmits the image information through an optical driving circuit, performs electro-optical conversion, and then the photodetector converts the detected tiny signal into an electrical signal, amplifies the signal amplitude, and then transmits the amplified signal to the video recorder, and finally displays the image information on the screen.

[0116] Light drive circuit design

[0117] Let U CC =15V,m=3%,β=20,U BEQ =0.7V,U LED =3.5V,I M =618mA,

[0118] From formula (5), we can see that if we want the transistor to have the maximum amplification factor when working, then

[0119] According to formula (4),

[0120] According to formula (6),

[0121] According to formula (7), let U CEQ =7.5V, then 7.5≈15-0.6R3-3.5, R3≈6.67Ω;

[0122] According to formula (8), U BQ =0.7+6.67×0.6=4.7V;

[0123] According to formula (9), if R1 = 10 kΩ, then R2 = 4.56 kΩ.

[0124] Optical receiving circuit

[0125] (1) Transimpedance amplifier circuit

[0126] Assuming the op amp is ideal, the typical value of GBP of OPA8045 is 1GMHz, and the total input parasitic capacitance C S =10pF,R f =10kΩ,f0=4.5MHz

[0127] According to formula (10), the -3dB closed-loop bandwidth of the circuit is:

[0128] According to formula (11), the gain of the circuit is:

[0129] According to formula (12), the compensation capacitance is:

[0130] (2) In-phase proportional amplifier circuit

[0131] like Figure 7 As shown, the gain of the in-phase amplitude amplifier circuit is:

[0132]

[0133] Among them, R1 is the feedback resistor, R3 is the balancing resistor, and R3 = R1 / / R2.

[0134] Let the circuit gain be 2, R2=500Ω, then R1=500Ω, R3≈250Ω.

[0135] like Figure 6As shown in the figure, this system is the same as the audio signal transmission system. The optical drive circuit adopts an emitter bias circuit; the optical receiving circuit is composed of a transimpedance amplifier and an amplitude amplifier, and the transimpedance amplifier selects the photovoltaic mode. However, in this system, the amplitude amplifier circuit selects a common-phase proportional amplifier, such as Figure 7 As shown, it has the characteristics of no gain loss, high input impedance, low output impedance, wide bandwidth, good stability, etc. It is suitable for processing high-frequency signals and can ensure the stability and accuracy of the input signal source.

[0136] The amplifier circuit has a wide bandwidth and can transmit high-frequency signals without causing significant attenuation or phase distortion, so it is suitable for processing high-frequency signal transmission. At the same time, it has good stability and is less affected by factors such as temperature changes, power consumption changes or load changes, so it can provide reliable amplification performance under various environmental conditions.

[0137] The analog signal is then transmitted to the recorder and displayed on the screen. The recorder selects a 4-channel analog coaxial recorder that is compatible with Hikvision's high-definition coaxial analog camera. The image information that has passed through the amplitude amplification circuit is transmitted to the 4-channel analog coaxial recorder through a coaxial cable, and then the analog signal is displayed on the screen through the VGA interface.

[0138] Visible light communication is an emerging communication technology that uses visible light in the 380nm to 750nm band as a medium. It transmits information by controlling the high-speed light and dark flashing of light-emitting diodes. Figure 8 As shown in the figure, VLC has an ultra-wide spectrum band (430THz), which can greatly expand the available bandwidth resources and break through the spectrum resource bottleneck faced by future communication networks.

[0139] The system selects the communication mode of intensity modulation direct detection. The system block diagram is as follows Fig. 9 As shown in the figure, it is mainly composed of modulation signal, optical transmitter, optical channel and optical receiver. Since this method does not require the use of complex modulation and demodulation circuits and external modulators, the system structure is simpler, the system failure points are reduced, and the adaptability is strong; and the required components and circuits are fewer, with lower implementation costs and faster response speeds, it can adapt to high-speed data transmission and is more competitive in the market.

[0140] Fig.10 This is the schematic diagram of the transmitting circuit, where LED1 detects whether the circuit is powered normally, LED2 transmits the signal through intensity modulation, and C3 and C4 filter the ripple of the power supply. R1~R4, C1, C2 constitute the light driving circuit, where R1 and R2 provide bias voltage for the base, R3 and R4 are DC feedback resistors, and C2 is a bypass capacitor to eliminate the negative feedback of the DC feedback resistor to the AC signal.

[0141] like Fig.11As shown in the figure, the receiving circuit consists of two stages of op amps. The first stage is a transimpedance amplifier, which detects tiny signals and converts the photocurrent into a voltage signal. The second stage is an inverting proportional amplifier circuit, which amplifies the signal amplitude by 10 times. C3 and R3 in the middle of the two stages of op amps form an RC low-pass filter, and C4 to C7 are filter capacitors used to eliminate power supply ripple.

[0142] Comparing the technology of the present application with the prior art, a segment of audio signal is transmitted, such as Fig.12 As shown, the yellow waveform is the audio signal at the input end, and the purple waveform is the output signal at the receiving end. The signal curves are basically the same.

[0143] like Fig.13 As shown in the figure, the input end is the audio signal, the yellow waveform is the output signal of the receiving end, and the purple waveform is the output signal after the bandpass filter. Compared with the yellow signal, the purple signal is clearer and some noise is filtered out.

[0144] Transmit image information, while the transmitter is the same, change the receiver circuit. The receiver uses the OPA820 op amp to make an inverting proportional amplifier. The gain-bandwidth product (GBP) of OPA820 is 280MHz, which meets the design requirements.

[0145] The circuit was physically welded and a single-frequency sine wave signal received by the PIN diode was transmitted. It was found that when the input signal frequency was 2MHz, the amplitude of the output signal was severely attenuated and there was almost no signal. The image information was transmitted using this circuit. The results are as follows: Fig.14 As shown, it was found that only black and white images could be transmitted.

[0146] To improve this, the receiving circuit selects a combination of a transimpedance amplifier and a common-mode proportional amplifier, and uses a secondary op amp to improve the overall bandwidth and gain. The transimpedance amplifier circuit uses the OPA8045 op amp (GBP is 1GHz), and the common-mode proportional amplifier circuit uses the OPA843 op amp (GBP is 800MHz), both of which meet the design requirements. The PCB of the designed circuit is drawn to reduce the influence of tin soldering on the signal. Fig.15 As shown, the visible light communication system can transmit color images.

[0147] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0148] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A visible light communication system based on intensity modulation direct detection, characterized in that: Select IM / DD communication mode. The optical communication system consists of two parts: audio signal transmission system and image information transmission system. Both the audio signal transmission system and the image information transmission system contain two main parts: the transmitting part and the receiving part. The transmitting part includes the optical driving circuit and the white light LED, and the receiving part includes the photodiode PIN, the transimpedance amplifier and the amplitude amplifier. The audio signal transmission system first generates an audio signal from the mobile phone, transmits the signal to the optical drive circuit, and drives the white light LED to transmit the audio signal while lighting. The PIN captures the light signal in the environment. The transimpedance amplifier selects the photovoltaic mode and is used in conjunction with the PIN to detect the weak photocurrent signal, convert the detected light signal into an electrical signal, and then transmits the electrical signal to the amplitude amplifier. The amplitude amplifier is an inverting proportional amplifier circuit that increases the amplitude of the tiny signal. The partially amplified signal passes through an active bandpass filter with a center frequency of 600Hz and a bandwidth of 100Hz. The amplified signals that have passed through the bandpass filter and those that have not passed through the bandpass filter are then transmitted to the speaker for signal output. The image information transmission system first simulates the camera to synchronously acquire the image signal in the environment and outputs it to the optical drive circuit, transmits the optical signal through the white light LED, the PIN receives the tiny light signal, and the transimpedance amplifier and the PIN convert the optical signal into an electrical signal, and then transmits the electrical signal to the amplitude amplifier, which is a common-phase proportional amplifier circuit, amplifies the amplitude of the small signal, transmits the amplified signal to the 4-channel coaxial video recorder for storage, and then transmits it to the display screen to display the processed signal or image in real time; The whole system uses the power box as the core of energy supply. The switch selects to power the audio transmission system and the image transmission system respectively. After receiving the power input, the voltage stabilizing module of the audio transmission system stabilizes the voltage of the audio transmission system to 12V. The stabilized 12V voltage enters the dual power module of the audio transmission system, converting the single power supply into dual power supply ±5V, which powers the transimpedance amplifier, inverting proportional amplifier circuit, and bandpass filter of the audio transmission system. After receiving the power input, the voltage stabilizing module of the image transmission system stabilizes the voltage of the image transmission system to 15V. The stabilized 15V voltage enters the dual power supply module of the image transmission system, converting the single power supply into a dual power supply of ±5V, and supplying power to the transimpedance amplifier and the in-phase proportional amplifier circuit of the image transmission system.

2. The visible light communication system based on intensity modulation direct detection method according to claim 1, characterized in that: Signal transmission is divided into audio signal and image signal. The specific transmission process is as follows: The audio signal passes through the optical driving circuit, which enables the white light LED to complete the normal lighting function and convert the electrical signal into an optical signal. Then the PIN converts the detected optical signal into an electrical signal, which is convenient for the system to process and amplify the amplitude. The amplified analog signal is then transmitted to the bandpass filter to filter out an audio signal and compare the audio signal before and after passing through the filter. The image information is generated by an analog camera, which passes through an optical driving circuit to drive the white light LED to illuminate and transmit the image information, and then the electro-optical conversion is performed. Then the PIN converts the detected tiny signal into an electrical signal, amplifies the signal, and then transmits the amplified signal to the video recorder, and finally displays the image information on the screen.

3. The visible light communication system based on intensity modulation direct detection method according to claim 1, characterized in that: The white light LED uses 12V 3W Purui lamp beads with high luminous efficiency and high color rendering.

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