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Abstract : This paper designs a multimedia car audio system based on 32-bit ARM microprocessor with RADIO, IRDA, MP3, DVD and other functions. This paper combines the complex environment of the car body, gives the system software and hardware design, and the realization methods of each part of the system, mainly introduces the design and system integration of the radio, MP3 software and hardware.Keywords : car audio; ARM; multimedia
introduction
Looking at the current domestic car audio products, most of them are still card machines or CD players, and need to increase the design and research and development of high-end car audio. This paper designs a car audio with functions such as Radio, IRDA, MP3, DVD, etc., which has high market value.
System hardware architecture
The hardware circuit part of the system is mainly composed of buttons, infrared remote control, MOTOR control, radio, MP3, DVD and LCD display module. The module part is controlled by the MCU through the corresponding communication protocol. In view of MCU's processing speed, peripheral functions and price considerations, 32-bit ARM processors are significantly better than 8-bit MCUs in terms of on-chip resources and cost performance. Here, the ARM7TDMI processor S3C44B0 is selected as the main control chip. The connection between the chip and the peripheral is shown in Figure 1.
Figure 1 MCU and various peripherals connection diagram
Here, the button module uses the AD conversion simulation inside the 44B0 chip, and the number of analog buttons can reach 210 theoretically, which can fully meet the design requirements of the system. The infrared remote control module adopts an infrared remote control head which is integrated with the transceiver, and receives the infrared code based on the NEC code. The output pin of the infrared receiving chip is connected to an interrupt pin of 44B0, and each time the receiving interrupt of the 32-bit data is interrupted, the timer interval is compared, and it is judged whether it is 1 or 0, thereby obtaining the transmitted user code. , control the corresponding system functions. The motor control module uses two H-bridge chips CMD6208 to control two DC motors, which are used to realize the horizontal entry and exit of the pallet and the vertical flipping action. The CMD6208 chip has four output modes for forward, reverse, brake, and idle operation of the motor. The DVD drive uses the DVC3500 series of ultra-thin slot-loading optical drives, effectively alleviating the contradiction between the volume and function of high-end car audio. Using a GPIO pin of the 44B0, the purpose of controlling the DVD function is achieved by transmitting an infrared code of the analog NEC protocol to the DVD.
Radio module design
The harsh environment inside the car produces various electromagnetic radiation and pulse interference. In addition, the external electromagnetic wave acts on the car radio. It is difficult for the ordinary radio circuit to reliably avoid the interference signal. This requires the car radio circuit to perform certain anti-electromagnetic interference, such as adding The metal casing is electromagnetically shielded and a filter circuit is added to the power source or the like. This design uses Chengdu Xuguang's TAF-3LMF radio head, which uses an all-metal housing to effectively prevent electromagnetic interference. The module is mainly an EEPROM 24C02 chip based on TDA7540B chip and an IIC interface. The TDA7540 is an AM/FM FM circuit chip with an internal mixer, IF amplifier, demodulator for AM/FM, and stereo decoder. It uses BICMOS technology to allow multiple tuning functions to be performed externally. Just use a few components. The EEPROM is used to store the values ​​of the registers of the TDA7540 chip and the various parameter values ​​set by the user. This module can receive signals in the frequency range of FM 87.5MHz ~ 108MHz, MW 522kHz ~ 1620kHz, its pin and the connection with 44B0 as shown in Figure 2.
Figure 2 radio circuit
SDA and SCL are connected to the IIC pin of 44B0, and ADJCH, AM, and SSTOP are connected to the three GPIO ports of 44B0. 44B0 performs data transmission through the internal IIC interface to complete data reading and writing.
Before searching, you must initialize the TDA7540 register. The initialization of the FM search station is: TunerReg[14] = 0x25; TunerReg[5] = 0x1B; TunerReg[6] = 0xAF; TunerReg[18] = 0xB4; TunerReg[19 ] = 0xCF; TunerReg[30] &=0x7F; TunerReg[31] &= 0x7F; The search process is shown in Figure 3.
Figure 3 search flow chart
MP3 design
The MP3 part includes the master MCU AT89C51SND1 and the audio DAC CS4330. This part of the design uses the AT89C51SND1 chip, which has MP3 hard decoding. 44B0 and AT89C51SND1 control the playback and pause of MP3 through UART communication. The serial port between the two can be directly connected. The SCLK, DSEL, DCLK, and DOUT pins of the AT89C51SND1 are connected to the corresponding pins of the CS4330 for output control. The connection to the SD card uses the SPI interface built into the chip to set the SD card to the SPI transfer mode for reading and writing MP3 files. The USB interface is mainly used to download firmware or debuggers.
AT89C51SND1 has ISP download function internally. When downloading firmware, open ATMEL's FLIP software, select AT89C51SND1 device under “Device†menu, and select “USB†or RS232 for firmware download under “Communication†under “Settings†menu.
Conclusion
The basic functions of this system have been realized. In the prototype test phase, the hardware and software are tested, which shows that this scheme has good feasibility.
references:
1.SAMSUNG.S3C44B0 DATASHEET.
2.ATMEL .AT89C51SND1 DATASHEET.
3.ST .TDA7540B DATASHEET.TAF-3LMF Module Description Chengdu Xuguang Company
4.ST . Driving An Analog Keyboard with the ST7 ADC
5. Zhao Yun, Guo Lili. The minimum embedded system architecture of S3C44B0X. Computer programming skills and maintenance.2007.1
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