Bluetooth audio player control board design

With the continuous development of bluetooth technology, bluetooth is applied to more and more electronic products, such as bluetooth music player is one of them. The music player was originally an early portable tape player, and later developed into a CD disc and then an MP3 player. Great changes have taken place in both shape and sound quality. The music of the MP3 machine is stored in the solid-state flash memory, which can realize the storage and playback of music, but when the memory is full, if you want to listen to other songs, you have to delete the original song and download the new song before you can play it, which brings some inconvenience. . Nowadays, the development of multimedia technology is getting faster and faster. As a consumer electronic product that often appears in life, the demand for music players is constantly increasing, and the competition is also constantly increasing, prompting manufacturers to actively adopt advanced technology to improve product competitiveness. The design of music players began to slowly add bluetooth technology, and the audio player with bluetooth function can enhance the user's entertainment experience, making music players with bluetooth function more and more used in various places. Audio players with Bluetooth function can bring consumers a more convenient music experience, and play an important role in today's rapid development of multimedia technology.

Aiming at the limitations of traditional music players such as not easy to carry and manual operation, the Bluetooth music player is designed to support wireless remote control technology, which can remotely control the playback of music. At the same time, functions such as pause, play, and up/down can also be realized on the player. At the same time, SD card and U disk are added, so that the product supports Bluetooth transmission and also supports SD card and U disk, realizing multi-mode transmission. Compared with traditional music players, it is more popular with the public.

1. Overall scheme design of Bluetooth audio player

The schematic flow chart of the design is shown in Figure 1.

AC4601, which uses Bluetooth chip as the main control chip, has many functions, supports Bluetooth remote control, USB, TF, etc., and can basically meet the design requirements. Among them, the Bluetooth module has no direct hardware embodiment in the circuit.

In the audio amplifier module, the audio can be amplified and transmitted with low distortion and low noise, and at the same time, the speaker can be driven to produce sound. Choose MIX3018 as the audio amplifier chip.

The main control chip decodes the audio received or read through Bluetooth, audio socket, SD card, etc., transmits the decoded audio to the audio amplifier for low distortion and low noise amplification, and finally plays the sound from the speaker. The function button circuit can control the start and pause of audio playback, the operation of the next song and so on. The power circuit supplies power to the entire system.

2. Bluetooth player hardware design

2.1 Main control module AC4601

The AC4601 chip is used as the main control chip of the entire audio player. AC4601 is a bluetooth chip launched by Jerry, which belongs to AC460N series. LQFP48 package, music in MP3 and WAV formats and music without lossy compression can be decoded by this chip. At the same time, it also supports the output of 24-bit DAC digital-to-analog conversion. The functions of AC4601 are generally divided into Bluetooth, plug-in card and radio.

The decoding system process in AC4601 is divided into two processes, one is the master decoding system process and the other is the slave decoding system process. The two processes are responsible for the command control of the decoding system. Operation response, the Slave channel is used to play the specified audio file, and the playback time and times are limited. The decoder thread is responsible for song decoding, such as MP3 and WAV. The system supports simultaneous decoding of multiple channels. The decoded data is superimposed through sound processing and output .

For a better Master decoding channel, its general program flow is as follows: first create a decoding process, then obtain system information, start to initialize the parameters of the decoding system, activate the music task after initialization, and start decoding. If there is an error in decoding, return to The step that waits for a system message. During the music playing process, if a button message is received, the message can be processed to control the pause, play, next song, etc. of the song. When a song is played, the system will automatically find the next song to play. If a new device is plugged in, the system will go to the latest plugged in device to find the song to play.

The decoding output will change. When the sound effect is successfully started, the sound effect obtained by decoding will be output to the DAC after the sound effect processing is completed; when the sound effect is invalid, the decoding output will be directly sent to the DAC.

2.2 Audio amplifier module MIX3018

The audio signal output by the main control chip is very weak. At this time, an audio power amplifier is needed to amplify the audio signal. The MIX3018 chip is used as the core of the audio amplifier circuit in the design. The function of the MIX3018 audio power amplifier is to amplify the relatively small input audio signal, increase its power and ensure the audio output with low distortion and low noise, and at the same time drive the speaker with relatively large power to make it emit sound. At the same time, a volume adjustment button is connected, and the volume of the sound played by the player can be adjusted through the volume adjustment button.

3. Audio player software design

The overall design of the software is to combine the MP3 decoding part and the playing part to realize the decoding while broadcasting, that is, the realization of real-time decoding. Sound is a continuous analog signal, which must be processed before transmission. The processing process is sampling, quantization, encoding, and finally pcm data, that is, pulse code modulation data, which is the source of MP3.

MP3 decoding can be divided into 9 processes in total: bit stream decomposition, Huffman decoding, inverse quantization processing, stereo processing, spectrum rearrangement, anti-aliasing processing, IMDCT transformation, sub-band synthesis, pcm output. MP3 decoding is dual-channel, and the decoding information of the two channels is decoded separately and then synthesized and filtered for output.

The bit stream decomposition is actually to open the MP3 file and read out the relevant header information, side information and scale factor information. The way of opening is binary mode, and the basis for reading information is the format definition during compression.

In the design, the AC4601 chip has its own hardware decoding function. You only need to call its pins and give it the corresponding decoding instructions to decode the acquired audio without additional software decoding. First select the corresponding mode, the system reads or receives music files, applies for decoding interface resources, and decodes and outputs to the audio amplifier module.

The Bluetooth protocol stack is the most important thing to realize the Bluetooth function. Mutual positioning, connection, transmission and exchange of data between two devices are all inseparable from the Bluetooth protocol. Logically, each unit of the protocol stack can be divided into three parts: application group, middleware protocol group, and transmission protocol group. The protocol contained in the transmission protocol group mainly has two functions. One is to enable the devices with the Bluetooth function to confirm each other's location, and the other is to create, configure and manage the physical logical link, which is convenient for other high-level protocol data. transmission. In the process of sound effect processing, the step of EQ equalization is a work that cannot be omitted. EQ adjustments are the audio changes of the high volume, midrange, and accent of the sound roll. Balanced EQ can make the music more beautiful, and the timbre of the instrument can be changed, as long as in the digital EQ, the size of the frequency band db can be adjusted.

epilogue

In life, Bluetooth audio players can also be applied to many places, such as Bluetooth headsets. Now high-quality Bluetooth headsets have become more and more popular. Bluetooth headsets can perform functions such as listening to music and making calls. The bluetooth audio player can also be applied in the car bluetooth, or in some other electronic devices. From the perspective of the system itself, the system is easy to operate and the functions realized are relatively simple. The hardware cost of the design is relatively low, and the fun brought by remote control music playback can be achieved. It is also a good choice for users who do not require high sound quality.

The above is the development example of Bluetooth audio player introduced by Shenzhen Zuchuang Microelectronics Co., Ltd. for you. If you have bluetooth headset solution development needs, you can trust us. We represent a variety of single-chip microcomputers, voice chips, dual-mode Bluetooth ICs, and wifi chips. Brands include Songhan MCU, Yingguang MCU, Jerry Bluetooth, Ankai Bluetooth, Allwinner, and Realtek. Our technical services include: PCB design, microcontroller development, Bluetooth solutions, software and hardware custom development, APP development, small program development, WeChat official account development, etc. It can also undertake the design of intelligent electronic products, the development of living appliances, the research and development of beauty equipment, the application of Internet of things platform, the smart home control system, the development of TWS earphones, Bluetooth earphone speakers, the development of children's educational toys, the design of electronic education products, etc.