1 Introduction to the new intelligent remote control campus wireless broadcasting system
The intelligent remote control campus wireless broadcasting system is a new campus wireless broadcasting system that integrates wireless communication, audio and digital technology. The campus wireless broadcasting system adopts the dual tone multi-frequency DTMF (Dual Tone Multi-Frequency) communication method of telephone dialing and receiving. Dual tone multi-frequency is a reliable and mature communication technology. Because it provides a higher dialing rate, it quickly replaced the dial pulse signaling used by traditional rotary telephones. In recent years, DTMF has also been used in interactive control systems, such as language menus, voice mail, telephone banking and ATM terminals. DTMF has low requirements for transmission circuits. It can receive and send signals through ordinary telephone lines. The transmission distance is long, and there are many types of general dual audio components available. The transmitter of the campus wireless broadcasting system adopts stereo wireless FM. In order to avoid the interference of the addressing control signal with the broadcast audio signal, the left channel is the broadcast audio signal, and the right channel is the dual audio signal for receiver addressing. The modulated RF signal is transmitted to the receiver of each broadcast point through the electromagnetic wave emitted into space. After the receiver receives the RF signal through the antenna, it detects and obtains the audio signal of two stereo channels. The left channel broadcast audio signal is sent to the power amplifier for amplification; the dual audio control signal of the right channel is sent to the dual audio decoding circuit for decoding to obtain the corresponding binary control code. The control code is sent to the single chip microcomputer in the receiver. The single chip microcomputer turns on or off the power of the power amplifier part of the receiver according to the machine number code set in the machine, so as to realize the function of fixed-point/partition control of the FM receiver of each related broadcast point. The block diagram of the intelligent remote control wireless broadcasting system is shown in Figure 1. The left side of Figure 1 shows the manual button, remote communication terminal, and PC, which are mainly used to realize the control function of the wireless broadcasting system. In addition to the control function, the PC can also provide the system with broadcast audio source signals.
2 Hardware Design of Campus Broadcasting System Control
The intelligent remote control campus wireless broadcasting system mainly includes four parts: FM transmitter, FM receiver, control system and broadcasting sound source. This article focuses on the control system of wireless broadcasting. The control system can be divided into three modes: manual key control, PC host computer control and remote telephone remote control. The key component of the entire control system is the digital addressing encoder, and various control methods will eventually control the entire wireless broadcasting system through the addressing encoder.
2.1 Digital encoder
The core components of the digital encoder are the single-chip microcomputer AT89C52 and the DTMF transmitter 9200. Manual key control, telephone remote control and PC host computer control will eventually use the single-chip microcomputer in the encoder to send the control information through 9200. The biggest difference between different control methods is that the control instructions for the entire wireless broadcasting system are sent to the single-chip microcomputer through different methods and means such as manual keys, remote communication terminals and PCs. The hardware structure of the encoder is shown in Figure 2.
In Figure 2, 8870 is a DTMF receiving chip, which is used to receive DTMF signals from remote telephones. 7289 is a serial interface chip that integrates input keyboard and output display, and is connected to manual operation buttons. After the control code obtained according to different control methods is sent to the single-chip microcomputer, the single-chip microcomputer sends the control code to the DTMF sending chip 9200 in the form of a serial interface. 9200 generates corresponding dual-audio signals according to different codes, and then modulates the dual-audio signals through the transmitter and transmits them into the air, reaching each receiver through the propagation of electromagnetic waves.
2.2 Manual control part
The core component of the manual control part circuit is: the integrated chip ZLG7289A that integrates keyboard input and output display. ZLG7289A has a serial interface function and can drive 8-bit common cathode digital tubes at the same time. Each digital display tube can independently control properties such as blanking and flashing, and provides circular left shift/circular right shift display instructions. ZLG7289A can also connect up to 64-key keyboard matrices, and the keyboard controller contains a de-jitter circuit.
When a key is pressed during manual operation, the key value is sent to the 7289 chip, and the 7289 then sends the key value to the single-chip microcomputer in the encoder. After the single-chip microcomputer processes the key value, it is sent as a control code to the 9200 in the encoder. In this way, the addressing control of fixed points or partitions can be finally realized by operating the keys. In the wireless broadcasting system, if there are many broadcasting points, multiple 7289 chips can be set in the manual key panel. Each 7289 chip has its own chip select signal to facilitate the single-chip microcomputer to select the device.
2.3 PC control part
The realization of PC control of the entire wireless broadcasting system depends on the dedicated broadcast control software, which has two main functions: management of sound source information and addressing control. In terms of sound source information, the shared resources of computers and even networks can be used to add various sound source information, which greatly enriches the content of wireless broadcasting. At the same time, it is also very convenient to manage the audio source program. Various playback management can be performed through the broadcast control software: timed playback, loop playback, audio source program selection, etc.; in terms of addressing control, when fixed-point or partition playback is required, the PC sends the corresponding code to the single-chip microcomputer in the encoder. Through the flexible interface function of the single-chip microcomputer, according to the different control requirements of the code, the corresponding control code is sent to 9200, thereby achieving the purpose of controlling the relevant wireless broadcast receivers. The PC and the single-chip microcomputer use serial communication, the PC is the upper computer, and the single-chip microcomputer is the lower computer.
2.4 Telephone remote control part
Telephone remote control can realize remote control of the entire wireless broadcast system. The remote control system uses program-controlled exchange signals (DTMF dual-tone multi-frequency signals, ringing signals, etc.) as system control commands, allowing users to use fixed phones or mobile phones to send DTMF dual-tone multi-frequency signals at the remote end to achieve remote control of the near-end wireless broadcast system equipment.
After the encoder receives the DTMF signal from the remote phone, it is decoded by a dedicated DTMF receiving chip, and the decoded signal is processed by the single-chip microcomputer. According to the dial-up transmitted from the remote communication device, the corresponding operation is performed. First, the password must be checked. If the password is correct, the corresponding operation can be further performed according to the information sent from the remote communication device (such as fixed-point or group opening/closing of the wireless broadcasting system related receivers, etc.), and finally the remote control of the campus wireless broadcasting system is realized.
The remote control circuit is mainly divided into the online circuit, the driving circuit, the DTMF decoding circuit, and the central control unit. Both the online circuit and the driving circuit are constructed with discrete components, which can further control the product cost. When the signal decoding circuit is connected to the user's telephone line, the system is called the online state; conversely, when the DTMF signal decoding circuit and the voice prompt circuit are disconnected from the user's telephone line, the system is called the offline state. The system should be in the online state only when the telephone remote control system is working. This can prevent the high-voltage ringing signal when the user calls the system and other high-voltage noise on the line from causing harm to the DTMF signal decoding circuit and the voice prompt circuit. The driving circuit is implemented by a relay. When the central processing unit confirms that the operation password is correct, it sends a control signal to energize the relay, so that the DTMF signal sent by the remote personal communication device can be sent to the DTMF receiving chip. The DTMF receiver and decoder uses CM8870, which is used to receive the DTMF signal, decode it, and send the decoded signal to the single-chip microcomputer in the encoder. The remote control circuit is shown in Figure 3.
Remote control is accomplished by both hardware and software. As shown in Figure 3, when the remote personal communication device dials the campus wireless broadcasting system number, a ringing signal EXTI is generated. After the ringing signal is rectified and filtered, it triggers the photocoupler transistor, the tube is turned on, and a valid CHECK signal is sent to the single-chip microcomputer. After receiving the CHECK, the single-chip microcomputer sends a TONE signal, starts the drive circuit, energizes the relay, closes the contacts, connects the external DTMF signal to the DTMF receiving chip CM8870, as shown in Figure 4. After that, CM8870 starts to receive the DTMF signal and decodes it to the single-chip microcomputer, which makes a judgment based on the pre-set operation password. If the password is correct, it continues to send a valid TONE signal and stays online. CM8870 continues to receive and decode it to the single-chip microcomputer, and the single-chip microcomputer continues to receive the code and performs the corresponding operation according to the agreement. For example: according to different codes, the receivers of the wireless broadcasting system are controlled at fixed points or in groups. If the password check fails, the microcontroller invalidates TONE, which in turn de-energizes the relay, disconnects its normally open contacts, and prevents external DTMF from being sent to the CM8870, putting the system in an offline state.
3 Software design of campus broadcasting system control
3.1 PC broadcast control software
Corresponding to the PC control part, it is programmed with VB, with a friendly interface and easy operation. Its functions mainly include modules such as playback task management, instant playback management, music library management and various settings, as shown in Figure 5.
3.2 Encoder control software
The manual control software is mainly used to process the addressing control and system timing control information input from the manual key panel. The remote control software mainly has the functions of ring current detection, password confirmation, output drive and further processing of remote control instructions. The control functions of the three control methods of PC control, manual control and telephone remote control will eventually be realized by the single chip microcomputer in the encoder. The encoder software is compiled in assembly language, and its functional block diagram is shown in Figure 6.
The main program corresponds to the manual key control part. If the system does not start PC control and there is no access to remote telephone control, the system enters the manual key control state and processes the control information of the manual key. The PC occupies the serial port interrupt of the microcontroller. The serial port interrupt service program is the interface program between the microcontroller and the PC. Its main function is to convert the control requirements sent by the PC into corresponding control codes and send them out through 9200. The remote telephone is connected in the form of external interrupt, and the ringing signal of the telephone call is used as the external interrupt request signal of the microcontroller. In the corresponding external interrupt service program, the microcontroller needs to confirm the operation permission password. If the password is correct, it will further receive the control information sent by the remote telephone dial-up through 8870, and process these control information accordingly to convert them into relevant control codes. This campus wireless broadcasting system has been debugged and run with good results.
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