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Loudspeaker Solution Development
Wireless loudspeakers have roughly gone through four stages of history. The first stage is the FM wireless loudspeaker, because the cost of FM is relatively low, and it is very attractive in terms of price; however, the operation of the FM wireless loudspeaker is more troublesome, the durability is relatively poor, and it is also easily interfered by radio signals. Buzz and whoosh. The second stage is 2.4G external wireless loudspeaker, which effectively solves most of the problems of the first stage loudspeaker; the working principle of the wireless mouse used in this stage of loudspeaker; it has no setting, no FM radio Interference with signals such as mobile phones, and the wireless range can reach 50 meters; but the socket of the receiver is easily damaged, and three devices need to be charged. The third stage is UHF built-in wireless, which effectively solves most of the problems of the second stage loudspeaker; it uses the principle of KTV microphone to start and connect. The wireless range is not wide enough, and the wall penetration is poor. The fourth stage is 2.4G built-in wireless loudspeaker, which effectively solves all the problems of the third stage loudspeaker; it has no setting, built-in 2.4G wireless, rejects all signal interference, no noise howling, wireless distance of 50 meters, can Wall penetration, easy charging and low power consumption. The wireless loudspeaker of the fourth stage adopts bluetooth technology.
It can be seen that the application of Bluetooth technology in loudspeakers solves the problems of wireless loudspeakers in terms of sound quality, operation, and use range. With the improvement of the quality of life, people's requirements for life enjoyment are also getting higher and higher. As a device used by people to protect the voice and realize sound amplification, the loudspeaker will become more and more popular with the improvement of sound quality and performance. Therefore, it is very necessary to study the application of Bluetooth technology in loudspeakers at this stage.
1. Overview of Bluetooth technology
Before understanding Bluetooth technology, let's take a look at 2.4G technology. 2.4G technology is a short-distance wireless transmission technology, which has the advantages of two-way transmission, strong anti-interference, long transmission distance and low power consumption. The so-called Bluetooth technology is a wireless transmission protocol based on 2.4G technology. Due to the different protocols used, it is different from other 2.4G technologies. In other words, Bluetooth technology is actually a short-range wireless communication technology.
Bluetooth is a technical specification for short-distance wireless communication. Due to its small size and low power consumption, it is used in most mobile portable devices that do not require high data transmission rates. The loudspeaker is just one of them. . Bluetooth technology mainly has the following characteristics:
(1) Applicable worldwide. Bluetooth works in the 2.4GHz ISM frequency band, which is an applicable frequency band licensed by the radio resource management departments of various countries.
(2) Voice and data can be transmitted at the same time. Bluetooth uses circuit switching and packet switching technology to support asynchronous data channels, three-way voice channels, and channels for simultaneous transmission of asynchronous data and synchronous language.
(3) Temporary peer-to-peer connections can be established. According to the role of the Bluetooth device in the network, the master-slave Bluetooth device can be set to realize the point-to-point communication of the master-slave device.
(4) High anti-interference ability. Since there are many wireless devices in the ISM frequency band openly used, Bluetooth technology uses frequency hopping to spread the spectrum, and the order of frequency hopping is pseudo-random, so it has strong anti-interference.
(5) The Bluetooth module is small in size and easy to integrate. Low power consumption. Open interface standards. In order to promote the application of Bluetooth technology, SIG has released all Bluetooth technology standards.
(6) Low cost. With the increasing demand of the market, more and more developments of Bluetooth chips and Bluetooth modules have been developed, resulting in a corresponding rapid reduction in the price of Bluetooth products.
2. Application of bluetooth loudspeaker
Before Bluetooth technology, most loudspeakers only realized the signal connection between the loudspeaker and the microphone, but could not realize the connection of signals such as computers and mobile phones. With the emergence of Bluetooth technology, the loudspeaker can not only amplify the microphone signal, but also connect to Bluetooth devices such as mobile phones and computers to achieve amplified sound. Like this, has brought new development space to loudspeaker. The loudspeaker is mainly composed of three parts: microphone, power amplifier circuit and speaker. Bluetooth technology is mainly used in the microphone and speaker of the loudspeaker. According to the use of loudspeakers, tour guides and teachers use the highest frequency. Next, we will introduce the necessity of using Bluetooth loudspeakers for tour guides and teachers.
2.1 bluetooth tour guide amplifier
We all know that tour guides often lead groups out and explain attractions to tourists on the way. When the tour guide uses a loudspeaker to explain the itinerary and attractions, the wireless loudspeaker is more convenient to carry and use than the wired loudspeaker. There are many varieties of wireless loudspeakers, which can basically meet these requirements. From the perspective of sound quality requirements, 2.4G wireless loudspeakers, UHF wireless loudspeakers, and Bluetooth loudspeakers can all meet these requirements. However, if the tour guide has to explain the scenic spots to everyone all the way, it will inevitably bring a certain level of demand to the voice of the tour guide, and if he does not explain, it will lead to insufficient understanding of the scenic spots by tourists. Then using computers or mobile phones to play scenic spot explanation audio to tourists can fully solve these problems. How to use computers and mobile phones to allow passengers to enjoy loud and clear explanations has become a test for tour guides. Some tour guides bring a large speaker in the car, and there are many problems with the sound quality played by some tour guides, which leads to various complaints from passengers. The appearance of bluetooth loudspeaker can fully solve these problems. First of all, the Bluetooth speaker is small in size and easy to carry; the sound signal is not easily disturbed, and the sound quality is good; the most important thing is that it can be connected to mobile devices such as wireless microphones, mobile phones, and tablet computers. For use with mobile phones, tablets, bluetooth microphones are a premium option for wireless loudspeakers. Considering the portability and sound quality of all equipment, it is very advantageous to use a Bluetooth microphone in the tour guide loudspeaker.
2.2 bluetooth teacher loudspeaker
During the lecture, the teacher needs to talk a lot, and the throat is easily damaged. In order to enable the students to listen to the class clearly, the teacher can protect the voice well. The application of loudspeakers among teachers is very extensive.
In addition to the same advantages as used in tour guides among teachers, Bluetooth loudspeakers also have two application characteristics. One is a portable Bluetooth speaker system; because the speaker is light and portable, it can be easily carried and used at any time. The second is a system with multiple bluetooth microphones and a bluetooth loudspeaker; teachers only need to bring a bluetooth microphone to use the loudspeaker in the classroom with the bluetooth loudspeaker; because the bluetooth technology is easy to connect, it greatly reduces the number of students in the school. The cost of using the loudspeaker also brings great convenience to each teacher.
Since most power amplifiers can only receive analog audio signals, the interfaces of the corresponding integrated circuits are almost all analog, so analog-to-digital conversion and digital-to-analog conversion need to be repeated. However, such a process introduces quantization noise, which degrades the sound quality, making it less than optimal. Digital power amplifiers have an absolute advantage in power consumption and volume, and have been widely used in car audio and subwoofer active speakers with high requirements. This paper designs a digital loudspeaker, which has the characteristics of simple circuit, short development cycle and high stability.
3. Overall scheme design of loudspeaker
The digital loudspeaker designed in this paper mainly uses a class D audio power amplifier component, the function of which is to amplify the weak signal from the audio source or the pre-amplifier, so as to meet the design requirements. The designed digital loudspeaker has the following functions H]: ① amplify the audio; ② adjust the tone; ③ adjust the volume.
The digital loudspeaker is mainly composed of 4 modules (see Figure 1), including audio input, frequency selection network, amplification module, and digital power amplifier. The functions of the 4 modules are as follows:
(1) Audio input. The detected sound is collected and sent to the control system. (2) frequency selection network. Tone adjustment is realized by using a frequency division network of resistors and capacitors. (3) Enlargement module. The signal voltage is amplified by an amplifying circuit composed of an operational amplifier. (4) Digital power amplifier. The principle of digital circuit is used to amplify the audio signal to drive the speaker. The frequency of the input signal is changed through the adjustment of the sliding rheostat, and then the frequency is adjusted to the expected value through the frequency selection network, and then the tone is adjusted through the voltage amplifier, and finally the signal is transmitted to the class D power amplifier chip. The power amplification is driven by current amplification to drive the speaker, and finally the design requirements and expected effects of digital signal amplification are achieved.
4. Hardware design of digital loudspeaker
4.1 Power circuit design
This article mainly adopts bridge rectifier circuit, the principle of this circuit is relatively simple. The power circuit converts the AC voltage of 220V into a DC voltage of 12V. The principle of the power circuit is shown in Figure 2.
Use the characteristics of the transformer to convert the 220V voltage into a low-voltage AC, then convert it into a pulsating DC through the bridge rectifier circuit and add it to the capacitor C9, and then generate a 15V DC voltage through filtering, and this part of the voltage is provided to the power amplifier; 15V The DC voltage generates a 12V DC voltage through the step-down effect of the LM7812, which meets the requirements of the operational amplifier.
4.2 Volume adjustment circuit design
The core device of the volume adjustment circuit is a potentiometer R10, and the main function of R10 is to divide the voltage. Slide the floating point on the rheostat according to a certain rule or ratio to produce different output values, thereby completing the adjustment and change of the volume.
4.3 Tone adjustment circuit design
The tone adjustment circuit design uses an inverse proportional operational amplifier, a frequency selection network is formed by resistors and capacitors, and the size of the capacitor is changed by changing the distance between the two plates of the capacitor and the facing area, thereby changing the frequency of the network to achieve tone adjustment.
4.4 digital power amplifier
The class D power amplifier converts the signal with almost zero loss, so the utilization rate of the power supply is very high. The design of this article is mainly based on Class D power amplifier. The power amplifier circuit consists of four components, namely circuit power supply, signal input, power amplifier processing and signal output n. The digital power amplifier chip adopts TDA8932 chip. After the input audio analog signal is processed by pulse width modulation, a pulse chain is formed according to a certain ratio, and the amplified signal is filtered out by a low-pass filter to obtain an amplified input signal waveform to drive the speaker. Finally, the purpose of digital signal amplification is achieved.
The digital loudspeaker designed in this paper mainly consists of four important components, namely power supply circuit, volume adjustment circuit, tone adjustment circuit and digital power amplifier circuit, and each component plays a vital role. The audio signal is amplified by the current to drive the speaker, and finally achieve the effect of audio amplification, tone and volume adjustment.
epilogue
With the updating of technology and the improvement of people's living standards, people's requirements for the quality of life are getting higher and higher. As one of the more mature new technologies, Bluetooth technology will be more widely used in wireless systems. In order to meet the needs of technological development, we should be committed to perfecting Bluetooth technology and making it more widely used.
The above are the details of the loudspeaker solution introduced by Shenzhen Zuchuang Microelectronics Co., Ltd. for you. If you have the electronic function development needs of the loudspeaker, you can rest assured to entrust it to us. We have rich experience in custom development of electronic products, and can evaluate the development cycle and IC price as soon as possible, and can also calculate the PCBA quotation. We are a number of chip agents at home and abroad: Songhan, Yingguang, Jieli, Ankai, Quanzhi, realtek, with MCU, voice IC, Bluetooth IC and module, wifi module. Our development capabilities cover PCB design, single-chip microcomputer development, Bluetooth technology development, software customization development, APP customization development, WeChat official account development and other hardware and software design. It can also undertake the research and development of smart electronic products, the design of household appliances, the development of beauty equipment, the development of Internet of Things applications, the design of smart home solutions, the development of TWS earphones, the development of Bluetooth earphone speakers, the development of children's toys, and the development of electronic education products.
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