CN103944635A - Voice broadcast system based on visible light communication - Google Patents

Abstract

The invention discloses a voice broadcasting system based on visible light communication, which includes a visible light transmitter and a fixed terminal with a photodiode, the fixed terminal is wirelessly connected to the visible light transmitter through visible light communication, and the visible light transmitter includes AD converter, parallel-to-serial data conversion module, light-emitting diode and light-emitting diode drive circuit, the described parallel-to-serial data conversion module adopts the first FPGA processor, and the described fixed terminal includes a photoelectric receiver, a serial-to-parallel data conversion module, a DA For the converter and the sound box, the serial-to-parallel data conversion module adopts the second FPGA processor. The present invention has the function of wireless transmission of voice signals by using visible light for lighting, and can be used for voice information broadcasting in places requiring all-weather lighting such as large shopping malls and subway stations, and can be used for hearing broadcasting in places requiring confidential communication such as examination rooms. The system is installed and maintained Convenience, wide application range, energy saving and environmental protection, scientific and reasonable, safe and reliable.

Description

Voice Broadcasting System Based on Visible Light Communication

technical field

The invention relates to a voice broadcast system based on visible light communication, which belongs to the field of multimedia information transmission and playback.

Background technique

In recent years, semiconductor (LED) lighting technology known as "green lighting" has developed rapidly, especially white LEDs are attracting more people's attention, and they are considered to be the next generation of lighting sources. It will eventually replace incandescent and fluorescent light bulbs that are widely used in offices and homes today. Utilizing the high-speed light-emitting response characteristics of LEDs, the signal is modulated to the visible light of LEDs for transmission, which can realize the high-efficiency mode of lighting and communication integration.

Sound broadcasting is usually used in stations, shopping malls, public venues, buildings, and residential areas for background music broadcasting, paging broadcasting, and forced-inserted disaster broadcasting. Sound broadcasting is also usually used in language test examination rooms to play listening test questions .

The traditional wired sound broadcasting system mainly includes sound sources, sound source management and control equipment, power amplifiers, output control equipment, sound restoration equipment, and power management equipment. It often adopts a bus system structure and uses RS-422, Ethernet and other interfaces. Using wired transmission. However, the traditional wired sound broadcasting system has the following disadvantages: First, the transmission line needs to be specially laid, and it is easy to generate parasitic capacitance to affect the system performance. problems such as gnawing, etc., increase the system maintenance cost; secondly, the wired transmission makes the speaker layout fixed and inflexible, and the sound broadcasting effect is difficult to guarantee; thirdly, the sound broadcasting of the wired transmission cannot be used in occasions with strict restrictions on electromagnetic interference; Finally, the traditional cable broadcasting system still has problems such as difficult wiring, complicated installation, poor expansion, and damage to the wall.

The wireless broadcasting system used to play listening test questions uses radio waves to transmit sound signals. It has the characteristics of no need for poles, wide coverage, unlimited expansion, convenient installation and maintenance, low investment, and beautiful and clear sound quality. However, the traditional wireless The broadcasting system has the following disadvantages: First, the traditional wireless broadcasting system cannot be used in places with strict restrictions on electromagnetic interference; secondly, the sound signal transmitted by the traditional wireless broadcasting system is easy to be monitored, causing problems such as leakage of test questions and cheating in the exam.

The visible light voice communication system that has emerged in recent years is still in its immature stage. The main problems are: the use of complex modulation and demodulation technology increases the cost of system implementation and maintenance; the transmission speed is low and the distance is short. In order to avoid the obvious flickering of LED lights, Technologies such as Maichester coding must be used, which also increases the complexity of the system.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the existing technology and provide a voice broadcasting system based on visible light communication, which has a compact structure, simple implementation, convenient installation and maintenance, wide application range, energy saving and environmental protection, scientific and reasonable, safe and reliable.

To achieve the above object, the technical solution adopted in the present invention is:

A voice broadcasting system based on visible light communication, comprising a visible light transmitter and a fixed terminal with a photodiode, the fixed terminal is wirelessly connected to the visible light transmitter by means of visible light communication, and is characterized in that:

The visible light transmitter includes an AD converter, a parallel-to-serial data conversion module, a light-emitting diode, and a light-emitting diode drive circuit. The described parallel-to-serial data conversion module adopts the first FPGA processor, and the AD converter simulates the voice generated by the sound source. The signal is converted into a parallel digital signal, and the first FPGA processor converts the parallel digital signal converted by the AD converter into a serial data stream to realize UART asynchronous transmission, and the LED driver circuit receives the serial data stream signal And drive the light-emitting diode to turn on and off at high frequency;

The fixed terminal includes a photoelectric receiver, a serial-to-parallel data conversion module, a DA converter and a sound box, the serial-to-parallel data conversion module adopts a second FPGA processor, and the photoelectric receiver receives the white light signal of the light-emitting diode And convert it into a serial data stream of an electrical signal, the second FPGA processor converts the serial data stream into a parallel digital signal to realize UART asynchronous reception, and the DA converter converts the parallel digital signal into a voice analog signal, and the speaker plays the voice analog signal.

The photoelectric receiver includes a photoelectric receiving circuit, the photoelectric receiving circuit is composed of a PIN photodiode, a transimpedance amplifier, a second-stage amplifier, a third-stage amplifier and a high-speed comparator connected in sequence, and the PIN photodiode is used to identify Light-emitting diode on and off signal.

The LED drive circuit is an AC current source circuit, which is composed of four current feedback operational amplifier circuits connected in parallel.

The visible light transmitter includes a power management module, and the power management module converts 220V alternating current into positive and negative 15V direct current.

The photoelectric receiving circuit includes a power management circuit, and the power management circuit converts 9V direct current into positive and negative 5V direct current.

In order to avoid the use of complex modulation techniques and coding techniques, thereby reducing system complexity and improving the accuracy of data transmission, the parallel-to-serial conversion module of the present invention uses FPGA processors to convert parallel audio digital signals into serial data streams and realize UART asynchronous transmission Function. That is, after receiving the parallel 8-bit data, it is sent out bit by bit starting from the low bit according to the fixed baud rate. The serial-to-parallel conversion module uses the FPGA processor to restore the serial data stream to a parallel audio digital signal and realize the UART asynchronous reception function. That is, after the level change on the channel is detected, the data of a character frame can be collected according to a fixed sampling rate, and the data bits in it can be transferred to other processing modules in parallel.

The photoelectric receiver of the present invention includes a photoelectric receiving circuit, wherein the photoelectric receiving circuit includes a photodiode, a transimpedance amplifier, a second-stage amplifier, a third-stage amplifier and a high-speed comparator. The photodiode recognizes the on-off signal of the light-emitting diode to generate a corresponding current signal, the transimpedance amplifier converts the current signal output by the photodiode into a voltage signal, and the second stage amplifier converts the voltage signal output by the transimpedance amplifier Amplification, the third-stage amplifier further amplifies the signal output by the second-stage amplifier to a certain value, and the high-speed comparator processes the signal output by the third-stage amplifier into a digital level signal, and the digital level signal is the photoelectric The output signal of the receiver or the received visible light signal, the output end of the photoelectric receiver is connected with the serial-to-parallel converter.

The voice broadcasting system based on visible light communication provided by the present invention has the following beneficial effects compared with the public broadcasting system which is widely used at present:

1. Visible light communication can be combined with the existing lighting power lines in the actual environment. There is no need to add additional power supply lines in the system layout. The transmitter of the voice broadcasting system based on visible light communication can be established by simply modifying the existing lighting system to achieve The purpose of making full use of existing resources, environmental protection and energy saving;

2. Visible light communication belongs to wireless transmission, which avoids the maintenance cost caused by the failure of the signal line, and also makes the layout of the speaker more flexible and easy to maintain;

3. LED is a green light source, and visible light is safe and harmless to the human body. This invention can be used in large shopping malls, subway stations and other places with dense crowds that require all-weather lighting and all-round voice broadcasting systems;

4. No electromagnetic interference, the present invention can be applied to occasions where electromagnetic interference is strictly limited, such as airplanes and operating rooms;

5. It is convenient to realize secure communication, and the present invention can be used in voice broadcasting application scenarios (such as hearing examination room) that require anti-eavesdropping.

6. Under the condition that the LED power is 1 watt, the system tests the attenuation characteristics of square wave signals with different frequencies. The system can finally realize the data transmission with a distance of 6 meters and a bandwidth of 2.5MHz. It does not require complex modulation and demodulation, coding and decoding technologies, and the system implementation and maintenance are very convenient.

Description of drawings

Fig. 1 is a structural block diagram of the use state of the present invention.

Fig. 2 is a block diagram of the connection structure of the visible light transmitter of the present invention.

Fig. 3 is a block diagram of the connection structure of the fixed receiver of the present invention.

Fig. 4 is a schematic circuit diagram of the LED driving circuit of the present invention.

Fig. 5 is a schematic circuit diagram of the photoelectric receiving circuit of the present invention.

Fig. 6 is the data frame format of the UART asynchronous serial port communication protocol adopted by the present invention.

Fig. 7 is a block diagram of UART sending program design in the present invention.

Fig. 8 is a block diagram of UART receiving program design in the present invention.

Detailed ways

The present invention will be further described below in conjunction with drawings and embodiments.

As shown in FIG. 1 , the voice broadcasting system based on visible light communication includes a visible light transmitter and a fixed terminal with a photodiode, and the fixed terminal is wirelessly connected to the visible light transmitter through visible light communication.

As shown in Figure 2, the visible light transmitter includes a power management module, an AD converter, a parallel-to-serial data conversion module, and a light-emitting diode drive circuit. Corresponding signals are connected in turn by wires between several modules.

In this case, the power management module can use an AC-DC conversion circuit to convert 220V AC power into government 15V DC power.

In this case, the parallel-to-serial data conversion module uses FPGA to realize UART universal asynchronous serial transmission.

Figure 6 shows the format of one frame of UART data, and the meanings of each bit of a character frame are as follows. Start bit: first send a logic "0" signal, indicating the beginning of the transmission character. Data bit: Immediately after the start bit, the number of data bits can be 4, 5, 6, 7, 8, etc., forming a character. Usually ASCII code is used. Transmission starts from the lowest bit, and is positioned by the clock. Parity bit: After adding this bit to the data bit, the number of "1" bits should be even (even parity) or odd (odd parity), so as to verify the correctness of data transmission. You can choose not to add it. Stop bit: It is the end mark of a character data. It can be a high level of 1 bit, 1.5 bit, or 2 bits. Since data is timed on the transmission line, and each device has its own clock, it is possible for two devices to be slightly out of sync during communication. So the stop bit not only signals the end of the transfer, but also provides an opportunity for the computer to correct clock synchronization. The more bits available for stop bits, the greater the tolerance for different clock synchronizations, but the slower the data transfer rate.

As shown in Figure 7, the program design of UART sending is basically the same as the idea of receiving. After receiving parallel 8-bit data, it will be sent out bit by bit starting from the low bit at a fixed baud rate.

As shown in Figure 4, the LED drive circuit uses a simple AC current source circuit to drive the LED, and the frequency of the drive diode can reach 2-3MHz, which cannot be recognized by human eyes. An AC current source circuit is designed with high output current and high bandwidth operational amplifier THS3091, and multiple operational amplifiers are connected in parallel to further increase the driving capability.

As shown in FIG. 3 , the fixed terminal includes a power management module, a photoelectric receiver, a serial-to-parallel data conversion module, a DA converter, and a sound box. Corresponding signals are connected in turn by wires between several modules. The white light signal becomes a serial data stream of electrical signals through the photoelectric receiver, then becomes a parallel digital signal through the serial-to-parallel data conversion module, and then becomes a voice analog signal through the DA converter, and the sound box plays the voice analog signal.

In this case, the power management module can use a positive 5V voltage regulator circuit and a DC-DC conversion circuit to convert the 9V battery direct current into positive and negative 5V direct current to power the chip.

In this case, the serial-to-parallel data conversion module uses FPGA to realize UART universal asynchronous serial reception.

As shown in Figure 8, the design idea of the UART receiving program is to collect the data of a character frame at a fixed sampling rate after detecting the level change on the channel, and transfer the data bits to other processing modules in parallel. The input of the level detection module is the signal input pin, and its function is to detect the start bit of the data. When it detects that the data signal changes from 1 to 0, it generates a high pulse to the control receiving module, indicating that a frame of data has been completed. Start; the baud rate timing module is a module that configures the baud rate. When a frame of data starts, this module regularly generates a high pulse to control the sampling of the receiving module; the control receiving module is the core module, and the configuration for the serial port is mainly 1 Frame 11-bit data, when used for one-way communication, the parity bit can be ignored. When a frame of data starts, this module samples data at the timing rate generated by the baud rate timing module, and waits for the 8-bit data bit to be received. , turn it into a parallel output, and notify other modules to read the data.

As shown in Figure 5, the photoelectric receiving circuit implements the signal conditioning function, including a three-stage amplifying circuit and a one-stage ultra-high-speed comparator. The first-stage amplifying circuit is a transimpedance amplifier built with the OPA657 chip, and the latter two-stage amplifying circuits are broadband low-noise amplifiers, and then output corresponding TTL level signals through the TLV3201 ultra-high-speed comparator behind.

In this case, when the LED power is 1 watt, the attenuation characteristics of square wave signals with different frequencies are tested. The system can finally realize the data transmission with a distance of 6 meters and a bandwidth of 2.5MHz.

The present invention is dedicated to wirelessly transmitting the voice signal from a microphone or other sound sources through an optical transmitter using visible light, and the photoelectric receiver receives the optical signal and restores the voice signal to the speaker for broadcasting. It can be used in subway stations, large shopping malls, museums, books, etc. Service broadcasts such as background music, emergency broadcasts such as fire alarms, and other business broadcasts in places such as museums, airplanes, and operating rooms. It has the characteristics of energy saving and environmental protection, flexible layout, convenient maintenance, low cost, and wide application range.

Claims (5)

1. the voice broadcast service system based on visible light communication, comprises VISIBLE LIGHT EMISSION machine and the fixed terminal with photodiode, and described fixed terminal and VISIBLE LIGHT EMISSION machine, with line-of-sight propagation wireless connections, is characterized in that:

Described VISIBLE LIGHT EMISSION machine comprises AD converter string data modular converter, light-emitting diode and LED driving circuit, described and string data modular converter adopts a FPGA processor, the voice analog signal that described AD converter produces source of sound changes into as parallel digital signal, a described FPGA processor changes into the parallel digital signal changing into through AD converter for serial data stream and realizes UART asynchronous transmission, and described LED driving circuit receives described serial data stream signal and drives the light on and off of light-emitting diode high frequency;

Described fixed terminal comprises optoelectronic receiver, string data conversion module, DA converter and audio amplifier, described string data conversion module adopt the 2nd FPGA processor, described optoelectronic receiver receives the white light signal of described light-emitting diode and changes into the serial data stream into the signal of telecommunication, described the 2nd FPGA processor changes into described serial data stream to realize the asynchronous reception of UART for parallel digital signal, described DA converter changes into described parallel digital signal into voice analog signal, and described audio amplifier is play described voice analog signal.

2. the voice broadcast service system based on visible light communication according to claim 1, it is characterized in that: described optoelectronic receiver comprises photoelectricity receiving circuit, described photoelectricity receiving circuit is made up of the PIN photodiode connecting successively, trans-impedance amplifier, second level amplifier, third level amplifier and high-speed comparator, and described PIN photodiode is for identifying the light on and off signal of light-emitting diode.

3. the voice broadcast service system based on visible light communication according to claim 1, is characterized in that: described LED driving circuit is alternating current source circuit, is composed in parallel by four current feedback operation amplifier circuits.

4. according to the voice broadcast service system based on visible light communication described in claim 1,2 or 3, it is characterized in that: VISIBLE LIGHT EMISSION machine comprises power management module, described power management module is converted to the alternating current of 220V the direct current of positive and negative 15V.

5. according to the voice broadcast service system based on visible light communication described in claim 1,2 or 3, it is characterized in that: described photoelectricity receiving circuit comprises electric power management circuit, 9V direct current is converted to positive and negative 5V direct current by described electric power management circuit.