1. Customer needs
A city-level key middle school in a city has a main teaching building with 20 classrooms on three floors, 60 meters long on each floor, and a small teaching building with 2 classrooms on the second floor, each building has a length of 15 meters and an experiment. There are 6 classrooms on the third floor of the building, each floor is 30 meters long, the school has a standard 200-meter runway, and a 350-square-meter auditorium. Now the school needs to build a campus intelligent broadcasting system to meet the requirements of education and teaching. The specific requirements of the English listening test are as follows:
1. The school broadcasting system is divided into 4 parts: classroom area, playground area, auditorium area, corridor area.
2. All 28 classrooms (20 teaching buildings, 6 experimental buildings, and 2 small second floors) require that each classroom can be independently controlled (point-to-point, point-to-group) and the volume of each terminal can be adjusted by itself. The speakers in the classroom can realize stereo broadcasting.
3. Aisle area, playground area, and auditorium area can realize individual broadcast of each area, combined broadcast of several areas, or whole broadcast.
4. When the DVD in the broadcasting room and the computer play the video, the video screen is displayed by the projector in the classroom, and the audio needs to be amplified by the speakers of the broadcasting system in the classroom.
5. Player DVD (with MP3, flash memory socket), deck (JVC digital display touch), digital tuner (excellent reception, with digital display), computer (graphic card with video output) requires clear and undistorted sound, The equipment is reliable in quality and good in use.
6. Using the remote auxiliary control system, the Academic Affairs Office and Sports Group can broadcast the teaching area, playground area, auditorium area, aisle area, etc. individually or in combination. The control requires easy operation.
7. The system construction is based on the principles of mature technology, stable operation, good effect, economical and practical, and easy upgrade.
2. Scheme design
According to the needs of customers, considering that the school may be relocated or expanded in the future, we design the school's broadcasting system as a comprehensive campus intelligent broadcasting system based on the principles of science, economy, practicality, and application. Addressing FM broadcasting system, the corridor, playground, and auditorium use constant pressure partition broadcasting system. The control system of the entire system is the intelligent broadcast control system designed and developed by Beijing Jinmai Video Technology Development Co., Ltd. The design of the entire system is simple, easy to implement, and economical. practical.
1. Audio source design
★ Digital sound source design
The digital audio source is the audio signal output by the computer. It plays the digital audio files in the computer, including MP3, WAV, MIDI and other audio formats. The characteristic of the digital audio source is that it can be automatically broadcast at regular intervals. The universal application of the school has gradually increased the demand for automatic broadcasting of music. Music ringtones, English listening training and exams are inseparable from the demand for automatic broadcasting. Therefore, our school broadcasting system has designed 4 sets of digital audio sources.
a. Digital audio source 1 is used for automatic timing playing of school music ringtones, eye exercises, background music for school attendance, etc.
b. Digital audio sources 2, 3, and 4 are used for personalized broadcasting for each grade or class, such as listening to the English listening teaching courses of this grade in the early self-study time at grade 7, 8, and 9 respectively, and conducting listening training to fully satisfy The need to broadcast different programs for different classes or grades at the same time.
★ Analog audio source design
DVD: DVD is the most commonly used analog audio source in schools, mainly used to play educational teaching discs.
Deck: The deck is mainly used to play various English teaching tapes. To ensure the quality, the deck uses the Japanese JVC brand.
Tuner: used to listen to and broadcast the English listening test content of radio stations, and important news.
Conference microphone: used for the principal's speech, the speeches of the teachers in charge, broadcasting announcements, holding parent meetings, etc.
Wireless microphone: The wireless microphone is mainly used for raising the flag in the playground and doing radio gymnastics. The teacher in charge speaks in the playground.
2. Design of FM broadcasting system
FM broadcast is to modulate the audio signal that needs to be broadcast into a radio frequency signal and send it to the broadcast receiving end through a radio frequency coaxial cable. The characteristic of FM broadcast is that it can broadcast multiple programs at the same time. There are different programs on the receiver side, and different users can listen to different programs according to their needs. This feature of FM radio is commonly used in English teaching in schools. For example, the three grades are trained in English listening at the same time. The FM broadcasting system is designed for the classroom end of the school teaching area. We have designed 8 sets of programs, that is, 8 channels, of which 4 channels play digital audio sources, and 4 channels play DVD, deck, tuner, and microphone analog audio sources. Another characteristic of FM broadcasting is the common cable transmission with the CCTV system. When we built the school FM broadcasting system, we only need to add the cable TV modulator.
★ Audio modulator design
Each channel of FM broadcast requires an audio modulator to realize the modulation and transmission of audio signals. This school requires 8 audio modulators for 8 channels. We chose the American PBI-3000FM agile audio modulation The output frequency range is 87-108MHz. In the national FM broadcast band, the modulation frequency of the audio modulator is continuously adjustable in steps of 0.1MHz. Avoid local FM radio stations to ensure the sound quality of school FM radio.
★ Mixer design
8 channels of audio signals are modulated into radio frequency signals by 8 audio modulators to form 8-channel FM broadcast. We use a PBI-4016C mixer to mix 8 channels of RF signals into one channel signal, and then use coaxial cable The broadcast signal is transmitted to the FM speakers in each classroom.
★ FM speaker design
The FM speaker is a GMTD-FM8A model independently developed and produced by our company. The receiving frequency is 87-108MHz, which corresponds to the frequency range of the audio modulator. It ensures that every signal sent by the front end can be received. The output power of the speaker is 10W The reception effect is stereo, which can fully meet the requirements of school broadcasting and teaching. The FM speaker also integrates the controller of FM broadcast to achieve the addressing control of each classroom speaker in the broadcast center, and each speaker is equipped with a dedicated remote control. The FM speaker can receive the infrared signal emitted by the remote control, and the remote control can be used to switch the FM speaker, switch the channel, and adjust the volume. There are 20 classrooms in the main teaching building of the school, 2 classrooms in the small teaching building, and 6 classrooms in the experimental building. A total of 28 addressable FM speakers are needed.
3. Design of constant pressure broadcasting system
The constant pressure broadcasting system is the most widely used broadcasting system. It is cheap, convenient to implement, and stable in performance. We design the corridors, playgrounds, and auditoriums of the school as a constant pressure zone broadcasting system.
★ Speaker design
â‘ Corridor speaker design (main teaching building, small teaching building, experiment building)
The main teaching building has 3 floors, each floor is 60 meters long, and the corridor has a suspended ceiling, so each floor is designed to install 4 GM-513 (3-6W) ceiling speakers. This speaker has high sensitivity, wide frequency response range, and sound quality. With beautiful and beautiful appearance, a total of 12 GM-513 ceiling speakers are needed in the main teaching building corridor, with a total power of 72W.
The test building has 3 floors, the corridor is about 30 meters, and the corridor has a suspended ceiling. Among the corridors on the second floor, no speakers are installed, and the speaker interface is reserved. Two GM-513 (3-6W) ceiling speakers are installed on the first and third floors, A total of 4 GM-513 are required, with a total power of 24W.
The small teaching building is on the second floor, each floor is about 15 meters, and each floor is designed to install a GM-356 (3-6W) wall-mounted speaker, a total of two, a total power of 12W.
According to school requirements, the corridor is divided into 4 areas, one area on each floor of the main teaching building, and one area on the small teaching building and experiment building.
â‘¡ Playground sound column design The school playground is a playground with a standard 200-meter runway. In addition to the usual collective exercises, flag raising, sports games, etc., the wind and rain playgrounds also need to make broadcast speeches. There must be a good analysis and reduction of music and vocals. In addition, the outdoor area is relatively open and open, so the choice of speakers must have a good frequency response range and sufficient power. Here, install 6 GM-418 (40W-60W) outdoor sounds for the playground area The total power is 360W, and the playground is a separate area.
â‘¢ Auditorium speaker design
The area of ​​the small auditorium is about 350 square meters, and the room is relatively high. The school mainly wants to use the broadcasting system in this area for English listening tests, which requires high voice effects for speakers. To this end, install four GM-606 (40W) wall-mounted speakers in this area, with a total power of 160W.
★ Power amplifier design
The power amplifier uses a feeder circuit with a constant voltage output, and the output voltage is 70V or 100V. According to the calculation, the design of the power amplifier is generally 1.3-1.5 times that of the total power of the loudspeaker. If the site noise is large, the transmission line is long, and the power must be increased, determine the actual site situation of the school Line loss and possible expansion of the receiving speakers. The power amplifier part of the school's constant-voltage zone broadcasting system is designed to be two, with a GM-8660P (660W) for the playground area. A pure post-stage constant-voltage amplifier is configured for the auditorium and corridor areas. (460W) One.
4. Control system design
★ Overall control design
The school's broadcasting includes two different public broadcasting methods: FM broadcasting and constant pressure broadcasting, but in terms of intelligent control, we use a control host and a set of control software, which can control FM broadcasting and fixed voltage broadcasting. FM broadcast can be controlled to broadcast to every point, we call it addressing control, constant pressure broadcast can be controlled to broadcast in every area, we call it partition control, different control methods are relatively independent, and do not interfere with each other .
â‘ Master computer
The main control computer is the core equipment of the campus intelligent broadcast system. It controls the hardware equipment of each part of the broadcast system through the broadcast control software, allowing the system to perform various broadcasts according to the needs of the school. The configuration of the main control computer can be popular. It plays a controlling role in the system. It is recommended that users do not use this host for other purposes, and do not connect to the Internet to avoid virus intrusion, because once the control host has problems, it will affect the operation of the entire intelligent broadcast system. The control system adopts the 485 bus control mode, which has the characteristics of strong anti-interference and long control distance. The intelligent broadcast system of our company has been proved to be very stable after many years of application by many large, middle and primary schools across the country. Another use of the control host is to provide 4 digital audio sources.
â‘¡Power controller
There are many audio source equipment and power amplifier equipment in the front end of the broadcast system. When the system is turned on every day, these devices must be powered. If you power on or power off these devices at the same time, it may cause excessive current to damage the equipment. Design a power controller. Under the control of the computer when the system is turned on, the power controller will sequentially power on the front-end equipment, and sequentially turn off the equipment when the system is turned off.
★ Addressing control
Addressing is a requirement of most primary and secondary schools in recent years. The traditional fixed-pressure zone broadcasting system uses physical partitioning. Once the system is built, it is difficult to change. Now the enrollment of many primary and secondary schools is changing every year, so each grade The number of classes also changes with the enrollment changes, and the corresponding classroom distribution must also change frequently. If the classroom uses a constant pressure zoning broadcast system, the physical zoning method cannot change the zoning according to the changes in the class classroom, so we put the school classroom Partly designed as addressable broadcast, addressable broadcast is to set an address code for each speaker, and then the system broadcasts according to one or several speakers specified by the user. The class name of each speaker can be changed, but the address code It is the same, any grouping or fixed-point broadcasting can be realized through software. For the overall beauty and generosity, our company integrates the addressable controllers of FM broadcasting into FM speakers. Each controller is controlled by the main control computer, which controls the switch of the designated speakers, listening channels, etc. At the same time, the speakers have digital displays. Displays the broadcast channel and status of the speaker.
★ Zone control
The school's constant pressure broadcasting system is divided into six areas. The school needs to broadcast to different areas according to different needs during automatic broadcast, such as ringing bells to all areas, raising flags to do radio exercises to playground areas, etc., we design for the system An 8-channel partition controller, controlled by the main control computer to automatically open the required broadcast area at a fixed time, and also has a manual function, which is convenient for temporary broadcast.
★ Sub-control system design
The school broadcasting room controls the daily regular broadcasting of the whole school, such as ringing bells, raising the flag, doing eye exercises, etc. However, other departments will have many regional temporary broadcasts, and they cannot go to the broadcasting room to control the broadcast every time. The auxiliary control system is convenient for other departments to realize remote control and temporary broadcasting in their offices. The school needs to configure two sets of auxiliary control systems for temporary speeches and announcements in the Academic Affairs Office and Sports Group. The auxiliary control system uses touch screen control to avoid occupying computer resources, and the operation is relatively simple.
★ Playground remote control system design
Addressing broadcasting and district broadcasting solve most of the school ’s broadcasting needs, but there is also a problem of remote control of the playground or square for the school, because in each school ’s daily flag-raising activities and radio gymnastics, the team must first be organized Sometimes, school leaders or teachers in charge also need to speak or notify some things, so in this case, using the timing broadcast system will often result in the formation of the team or the leader ’s speech is not finished, the national anthem or radio gymnastics music It has already sounded, or the formation has been lined up, and the teacher has finished speaking. The time for playing music has not yet arrived. The teacher and classmates need to stand there and wait. Therefore, when flag raising activities and radio gymnastics are held in the school, the automatic The regular broadcast mode can only be played manually. However, the broadcast room of the general school is in a room in the building, and the situation of the playground is often not visible. Manual broadcast is still very inconvenient, so we designed for playground broadcasting A set of broadcast wireless broadcast control system to solve the problem of remote manual playback in the playground. The system uses remote control by wireless remote control. Control panel remote control radio room of the national anthem, music players and other broadcast gymnastics, stop, for music and so on.
Third, the main functional characteristics of the system
★ Auto-play function ---- The system can automatically play radio exercises, eye exercises, national anthem, athlete march, preparatory music bell, class music bell, class music bell, wake-up number, etc. through the auto-play software according to the schedule set by the school. , And other optional radio music and programs in schools such as news and English teaching programs.
★ Pre-scheduled playlists ---- According to the teaching and management needs of the school, the system can pre-schedule the playlists for one day and one week After the computer is turned on every day, the system will automatically judge the day of the week, and then automatically play according to the arranged playlist. Playlists can be stored, modified, and edited.
★ Cycling function ---- After arranging a week's play schedule, it can be played in a loop throughout the year without resetting every week.
★ Large playback capacity ---- Because it is automatically broadcasted by computer, thousands of ringtone music, various radio exercises, eye exercises, classroom music, various language teaching, English teaching can be used The programs are stored in the computer to form a sound file material library for selection when arranging playlists, and can also play audio files on the disc.
★ Play multiple file formats ---- The computer broadcast system can play WAV, MID, WMF, MP3 and other audio file formats, while supporting CD discs to play various music programs.
★ Set Play Identifier ---- You can set various play identifiers according to the play content, such as class bell, class bell, inter-class exercise, etc.
★ Play temporary broadcast ---- The system is divided into manual and automatic modes. If the school has temporary broadcast content to be played, it can end the automatic playback state at any time and enter the manual playback state to play.
★ Divisional control function ---- The system can control the speakers of playgrounds, corridors, campuses, etc. to play regularly according to the different contents and needs through the partition controller.
★ Power control function ---- Similarly, the power controller can sequentially power on other devices in the broadcast control room when the system is turned on, and sequentially power off these devices when the system is turned off, to avoid damage to the device due to excessive current.
Main functions of multi-channel addressable FM broadcasting system:
1. Multi-channel stereo playback
The system can provide dozens of stereo playback capacity (87MHz-108MHz) to meet the teaching and examination needs of different classes and grade language courses, as well as various needs of campus broadcasting. The traditional broadcasting system generally only has the functions of the principal's speech, playing music, radio exercises, etc., and intelligent FM broadcasting can build multiple sets of broadcast programs according to the needs, and each listening point can also listen to different programs according to different needs, providing students with multiple content, Multilingual campus radio program.
2. Authorization management
The main control system adopts computer control, visual operation interface, intuitive control interface and simple operation. The operation platform of the central control room can be used to authorize management of the classroom, control the switching of classroom speakers, listening channels, etc., and have control priority. That is, when the main control room controls the speakers at the classroom end, the remote control at the classroom end can only control the volume of the speaker volume, but cannot control the switch of the speaker and the channel to listen to, so as to ensure the normal conduct of the listening test and listening training.
3. Power management
The central control room can control the power switch of the FM speaker in a classroom or all classrooms through the automatic playback host to ensure that the speaker power is turned off when there is no broadcast, to avoid crosstalk from external signals and affect the teaching effect.
4. Scheduled playback
The automatic playback control host can automatically switch the machine on and off according to the needs of the school, and automatically play the bells, radio exercises, eye exercises, national anthem, etc., to achieve unattended operation.
5. Multi-channel digital playback
The automatic playback control host can broadcast multiple digital audio files at the same time, which has met the needs of multiple teachers or multiple grades for simultaneous English listening training and exams.
6. Fixed-point broadcasting
Can realize the point-to-point directional broadcasting function, according to the need to broadcast a classroom individually, or free group broadcasting to multiple classrooms.
7. Full channel reception
FM speakers can receive more than 60 sets of broadcast programs at the same time. When the system program source is increased, there is no need to replace the speakers, just add the front-end modulator.
8. Flexible channel setting
The frequency adjustment of the modulation end and the receiving end of the system are continuously adjustable. The channel setting can be carried out on site. When the local FM station interferes with the school's FM broadcast, the frequency of the front and back ends can be adjusted at any time to avoid interference Channels to ensure the quality of broadcasting.
9. Remote control function
The controller can perform channel setting, storage, deletion and other functions through the remote control. You can control the storage, deletion, channel addition and subtraction, and volume addition and subtraction of the channel through the remote control.
10. LED frequency display
The controller is equipped with 3 LED digital tubes, which can display the frequency of the current receiving channel.
11. PLL phase-locked loop frequency stabilization
The system uses PLL phase-locked loop frequency stabilization technology in the receiving part to ensure that the receiving frequency is not affected by changes in ambient temperature, thereby ensuring the listening effect of the broadcast.
4. System Topology
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