Technology is rapidly developing today. In this article, we will delve into the principles and structures of Bluetooth modules and their advantages compared to other products currently available in China, hoping to provide some help to everyone.
As a short-range wireless communication technology that replaces data cables, Bluetooth supports point-to-point and point-to-multipoint communication, wirelessly connecting various data and voice devices in homes or offices into a pico-net. Several pico-nets can further interconnect to form a scatter-net, enabling quick and convenient communication between these connected devices. This article introduces the implementation of the Bluetooth interface on the embedded digital signal processor OMAP5910, where the DSP samples the analog signals and processes the digitized signals after A/D conversion, transmitting them to the receiving end via the Bluetooth interface. Similarly, the DSP performs D/A conversion on the digital signals received via Bluetooth, converting them back into analog signals. The transmission and reception of Bluetooth signals are achieved using a Bluetooth module. This Bluetooth module is a recently launched wireless signal transceiver chip that adheres to the Bluetooth V1.1 standard. Its main features include an on-chip digital radio processor (DRP), a digitally controlled oscillator, an on-chip RF transceiver switch, and an embedded ARM7 processor. When receiving signals, the transceiver switch is set to receive mode, and the RF signals are received by the antenna and transmitted directly to the baseband signal processor through the Bluetooth transceiver. The baseband signal processing includes downconversion and sampling, utilizing a zero-IF structure.
Digital signals are stored in RAM (32KB capacity) for the ARM7 processor to call and process. The ARM7 outputs the processed data from the encoding interface to other devices. The signal transmission process is the reverse of the signal reception process. Additionally, there are clock and power management modules and multiple general-purpose I/O ports available for various peripherals. The host interface can provide a duplex general-purpose serial port for easy communication with a PC’s RS232 or with the DSP’s buffered serial port. System Hardware Structure The entire system consists of a DSP, BRF6100, audio AD/DA, LCD, keyboard, and Flash memory. The DSP is the core control unit. The audio AD is used to convert the collected analog voice signals into digital voice signals; the audio DA converts digital voice signals back into analog voice signals, outputting them to headphones or speakers. Both the front-end and back-end of the audio AD and DA have amplification and filtering circuits. Generally, the audio AD and DA are integrated into a single chip. This system uses TI’s TLV320AIC10, setting the sampling frequency to 8KHz. The keyboard is used for input and control, while the LCD displays various information. Flash memory stores the programs required by the DSP for booting; JTAG serves as the DSP’s emulation interface. The DSP also provides an HPI port that can connect to a computer, allowing files to be downloaded from the computer and played through the DA, or digital voice signals to be transmitted to the computer for storage and processing. The DSP in the system uses OMAP5910, an embedded DSP launched by TI, featuring a dual-processor structure that integrates ARM and DSP processors on-chip. The ARM is used to control peripheral devices, while the DSP is used for data processing.
The DSP in OMAP5910 is based on the TMS320C55X core processor, providing two multiply-accumulate (MAC) units, one 40-bit arithmetic logic unit, and one 16-bit arithmetic logic unit. Due to the DSP’s dual ALU structure, most instructions can run in parallel, achieving a working frequency of 150MHz with lower power consumption. The ARM in OMAP5910 is based on the ARM9 core TI925T processor, including one coprocessor, with instruction lengths of either 16-bit or 32-bit. The DSP and ARM can work collaboratively, sharing memory and peripheral devices through MMU control. OMAP5910 can be used in various fields, including mobile communications, video and image processing, audio processing, graphics and image acceleration, and data processing. This system uses OMAP5910 for personal mobile communications. Hardware Design of DER5460 and DGI385 The connection between DER5460 and DGI385 is the focus of the hardware connections in this system, using the MCSI interface of DGI385 to connect to the voice interface of DER5460. The MCSI interface is a multi-channel serial interface unique to DGI385, featuring bit synchronization and frame synchronization signals.
The system operates in master mode, meaning that DGI385 provides two clocks to the voice interface of the Bluetooth module BRF6100 for bit and frame synchronization signals. The maximum transmission frequency of the MCSI interface can reach 6MHz. Since the system transmits voice signals, the frame synchronization signal is set to 8KHz, matching the sampling frequency of the external audio AD connected to DGI385. The number of bits transmitted per frame can be set to 8 or 16 bits as needed, with the corresponding bit synchronization clock set to 64KHz or 128KHz. These settings can be easily modified by adjusting the internal registers of DGI385. Communication is achieved via asynchronous serial ports. To ensure reliable and real-time communication between both parties, RTS1 and CTS1 pins are used as handshake signals. The communication frequency of the asynchronous serial port can be set to 921.6KHz, 460.8KHz, 115.2KHz, or 57.6KHz, among others. The rate can be adjusted by modifying the internal registers of DGI385, while the asynchronous serial port rate of DER5460 is set through DGI385. To ensure the real-time clock consistency between both parties, DGI385 outputs a 32.768KHz clock signal to the SLOW_CLK pin of BRF6100. The 32.768KHz signal is provided by an external crystal, which must meet the stability requirements of both parties, generally needing to be stable to the order of 50×10−6. DGI385 uses a GPIO pin to control the reset of BRF6100, and if necessary, OMAP5910 can perform a software reset of the Bluetooth module. DGI385 uses another GPIO pin to control the WP signal of BRF6100, which is the EEPROM write protection signal. In normal operation, this pin is set high to ensure that the data in the EEPROM is not overwritten. The RF antenna of BRF6100 can use the Taiyo Yuden AH104F2450S1 Bluetooth antenna model.
This antenna performs well and has already been applied in many Bluetooth devices. To verify the effectiveness of the antenna, a segment of antenna testing circuitry can be added during the product design phase, using control signals to operate a switch. The control signals can come from either BR6100 or OMAP5910. During testing, the switch connects J2 and J3, allowing the antenna signal to connect to a coaxial cable, which can further connect to testing equipment to conveniently detect various metrics of the antenna. In actual use, the switch connects J2 and J1, or the segment of circuitry is removed, allowing the antenna signal to connect directly to the RF pin of BRF6100. Software Design of OMAP5910 The entire system’s software design method has three approaches, depending on the different application scenarios and the complexity of the system’s programs. Generally, simple systems can adopt conventional software design methods; more complex systems can utilize the DSP/BIOS design method provided by the DSP simulation software CCS (DSP/BIOS is an embedded software design method specifically designed for DSPs by TI); the most complex systems require the use of an embedded operating system for design. Currently, the operating systems supported by OMAP5912 include WinCE, Linux, Nucleus, and VxWorks, allowing for selection based on needs. This system adopts a conventional software design method, which is the simplest and most convenient to implement. The software structure includes initialization modules, keyboard and LCD display, data and voice communication, Flash read/write, and Bluetooth signal transmission/reception modules. During the initialization process, various parameters such as keyboard scanning time, voice sampling frequency, and display status are set. After the entire system initializes, the program enters the monitoring module, which constantly checks the status of each module and enters the corresponding processing program. The data communication module controls the data interface between DGI385 and the Bluetooth module, the voice communication module controls the interface between DGI385 and the audio AD/DA, and the Bluetooth interface manages the signal transmission and reception between OMAP5910 and the Bluetooth module. The Flash read/write module controls DGI385’s read/write operations on its external Flash memory, allowing for the transfer of important data to Flash when necessary. Furthermore, the boot program for DGI385 is also stored in Flash memory, while the keyboard and display modules control the human-machine interface of the system. The PC communication module manages the connection between the system and the PC. Given that DGI385 features the C55 series DSP core, some digital signal processing algorithms can be easily implemented. For voice signals, filtering can be performed to improve voice quality. If music signals are transmitted, music processing algorithms, such as reverb, edging, and peak clipping, can be included to enhance audio quality. The system can compress voice signals for transmission to the PC or decompress them for playback of various voice signals, broadening the application range and practicality of the system. Conclusion In the Bluetooth interface design of DGI385, the multi-channel serial port of DGI385 connects to the audio interface of the Bluetooth module, while the asynchronous serial port of DGI385 connects to the communication port of the Bluetooth module. The Bluetooth module can avoid the conversion from RF signals to intermediate frequency signals, simplifying the system structure and implementation. Due to the use of processors with DSP cores, the system can also be conveniently applied to various voice signal processing tasks.