Design and Development of Wireless Communication Module Based on Bluetooth Chip

Design and Development of Wireless Communication Module Based on Bluetooth Chip

Abstract: In this paper, a Bluetooth wireless communication module is designed using BlueCore2-External Bluetooth chip, FB2520 band-pass filter, balun and LTCC ceramic antenna. The communication module can replace the cable and be effectively applied to the industrial site with complex and changeable environment, and realize the wireless communication of field devices, access points, handheld communicators and other devices. The actual test results show that the wireless communication module introduced in this paper is stable and reliable.

1 Introduction

Bluetooth technology is an open, short-range wireless communication technology standard. It works in the global 2.4GHZ ISM frequency band and uses frequency hopping spread spectrum technology. It can be used to achieve fixed devices and mobile devices at close range through wireless connection. Inter-network interconnection, to achieve flexible, safe, low-cost, low-power data and voice communication between various digital devices, to achieve a full range of data transmission.

The industrial site environment is harsh, and workers in some places are even difficult to access. Especially in some industrial environments, it is forbidden to use cables (such as ultra-clean or vacuum-enclosed rooms) or it is difficult to use cables to transmit data (such as high-speed rotating equipment, high-altitude equipment, and discomfort Due to the strong corrosion and harsh environment of wiring), using wireless communication technology such as Bluetooth to replace the cable to realize the data transmission between the field device and the monitoring network can effectively solve the above problems. To this end, this article designs Bluetooth wireless communication modules for industrial field devices, access points, handheld communicators, etc. This module has the characteristics of small size, fully embedded Bluetooth protocol, reliable performance and flexible networking. The feasibility of applying Bluetooth technology to industrial control systems is verified.

3 Hardware design of Bluetooth module

The hardware block diagram of the Bluetooth module is shown in Figure 1. It includes BlueCore2-External (BC212015) Bluetooth chip, SST39VF800 FLASH chip, FB2520 band-pass filter + balun, LTCC ceramic antenna, etc. The power supply is introduced by the supporting main equipment, and after the power module level conversion, it provides the required + 3.3V and + 1.8V power for the Bluetooth main chip, memory, band-pass filter, and balun. Each module will be introduced separately below.

3.1 BlueCore2 chip introduction

The Bluetooth module uses the BlueCore2-External (BC212015) chip. BlueCore2 is a single-chip Bluetooth chip that integrates baseband and radio frequency in the ISM (industrial, scientific, medical) band of 2.4GHZ launched by the British CSR company.

The internal structure of the BlueCore2-External chip is shown in Figure 1. The chip mainly integrates 32Kbyte on-chip RAM, DSP, MCU, RF front-end and various I / O ports. Various I / O ports include SPI, UART, USB, PIO, PCM, I2C and other interfaces. Among them, SPI, UART, USB interfaces are mainly used to transmit data; I2C bus is used to link EEPROM; PIO interface is a programmable interface; PCM interface is used to transmit voice; the maximum transmission rate of UART interface in BlueCore2 is 1.5Mbps, which can reach The data transmission rate of 723.2kbps specified in the Bluetooth standard.

3.2 Storage circuit

Since the Bluetooth chip does not have its own protocol stack, a FLASH is needed to store the protocol stack and application software. In this design, one of the SST39VF series from Silicon Storage Technology (SST) is selected, and the flash memory model is SST39VF800. SST39VF800 is a successful example of SST multi-purpose high-precision CMOS flash memory technology. It uses discrete gate circuit component design and oxidation channel injection technology, which greatly improves its storage reliability, and its process and performance are far superior to other competitors. In addition, SST has specially optimized the performance of SST39VF800 for portable devices, which makes it consume less energy during running, and the program execution speed is faster, which is more suitable for portable devices. According to the size of the Bluetooth protocol stack, the 8Mbit SST39VF800 is used, the reading time is 70ns, and the operating voltage is 2.7 ~ 3.6V. In order to meet the stringent requirements of the industrial site, the model that supports the industrial temperature range of -20 ℃ ~ + 85 ℃ is selected.

3.3 Bandpass filter + balanced unbalanced converter (Balun)

Generally, the RF transmitter outputs two differential signals TX_A and TX_B, and its output characteristics are balanced (symmetrical). The antenna output cable is 50 ohm unbalanced coaxial cable. When the coaxial cable is directly connected to a balanced system, the coaxial cable not only has high-frequency current inside the shield, but also has high-frequency current outside the shield. However, this will cause unnecessary coupling and cause a lot of interference. In severe cases, even the surrounding equipment will not work properly. Therefore, it is necessary to connect a balun between the antenna and the output of the transmitter. The band-pass filter is generally a passive device. Its function is to filter out signals in the frequency band that the receiver does not need, and to provide selective signals for the low-noise amplifier (LNA) to reduce interference. In this design, Taiwan's ACX company's integrated band-pass filter + balanced unbalanced converter device FB2520 is used. The band-pass filter and balanced-unbalanced converter are integrated together. The integration is higher and the circuit board's Area, the device has the advantages of small size, low insertion loss, etc., and can well complete the conversion of the balanced to unbalanced end and the function of band-pass filtering.

3.4 Power module Bluetooth module required

There are two kinds of voltages, 3.3V and 1.8V, of which 1.8V is used to power Bluetooth chips and band-pass filters + balanced unbalanced converters, and 3.3V is used to provide voltage for the peripheral I / O pins of FLASH chips and Bluetooth chips. Since the voltage introduced from the main device is 3.3V, a DC-DC chip is required on the Bluetooth module to realize voltage conversion. In this design, the XC6204B182MR high-speed LDO conversion chip widely used in mobile phones is used for 3.3V to 1.8V voltage conversion. The maximum output current of the chip is 150mA, and the output voltage range is 1.8V-6V, which fully meets the power requirements of the Bluetooth module.

3.5 Crystal oscillator CSX-5032

The selected crystal oscillator is CSX-5032, which is a SMD crystal unit made on a lead-free surface. The highly reliable ceramic hermetic package ensures the stability of the component at high frequencies and excellent solderability in a wide range of applications such as PHS, GPS handheld devices, Bluetooth, WLAN, etc. We have selected a 16MHz model with an external size of 5mmX3.2mm, a frequency tolerance of 25 ° C of + -10ppm, and a frequency stability of + -5ppm.

4 Software design of Bluetooth module

The software design of the Bluetooth module is divided into two parts: protocol layer loading and module initial parameter setting. The Bluetooth protocol provides a complete solution for a variety of applications built on Bluetooth technology, but for different applications, only a few of the Bluetooth protocols are generally used, and it is not necessary to use all the functions it provides for each protocol. .

4.1 Protocol layer loading

As shown in Figure 2, this module is mainly used in industrial wireless communication, so only the baseband (including LC), LM and HCI (host control interface) protocol layers are loaded in the external FLASH of the module. Among them, HCI provides a command interface for the baseband controller and link manager in the Bluetooth hardware, so as to achieve access to the hardware status register and control register, especially the interface provides a unified access mode for the Bluetooth baseband. Loading these protocol layer modules implements the complete Bluetooth link control and embedded HCI protocol, shielding the two hardware protocol layers of radio frequency and baseband. Future application development can start directly from the HCI layer. By encapsulating the HCI protocol layer, standard HCI interface functions can be generated to provide a complete platform for upper-layer application development.

In the case where the external host has a UART or USB interface and the Bluetooth module is compatible with the signal level of the host, no additional auxiliary circuits are needed, and the Bluetooth module can be directly connected to the host.

Figure 3 is a schematic diagram of the connection between the host and Bluetooth hardware. The host controller interface (HCI) provides a general interface for accessing Bluetooth hardware capabilities. The HCI layer implements HCI commands for Bluetooth hardware by accessing baseband commands, link manager commands, hardware status registers, control registers, and event registers. There are several intermediate layers between the HCI driver of the host system and the hardware HCI firmware of the Bluetooth, also known as the host controller transmission layer, which provides the ability to transmit data. The goal of this layer is to be transparent. The host controller driver does not care whether it is on the UART or USB. UART and USB cannot process the data sent by the host controller driver to the host controller, so that the host controller interface and The host controller can be upgraded without any impact on the transport layer.

4.2 Initial parameter setting of the module

The Bluetooth module does not work after loading various protocol layers, and the initial parameters of the module need to be set according to different hardware designs. The initial parameter setting based on the bluecore2 Bluetooth chip is also called PSK setting, which can be achieved through the BLUELAB integrated development environment or PS Key setting software, as shown in the figure for the ps key setting interface.

5 Bluetooth module application examples

As shown in Figure 4, take Bluetooth hand-held communicator and Bluetooth valve positioner as examples. The Bluetooth module performs serial (UART) full-duplex communication with the control board in the valve positioner. Various parameters such as the valve position value and upper limit of the valve positioner are sent to the Bluetooth module through the serial port and sent to the Bluetooth module by wireless communication. Bluetooth hand-held communicator, the hand-held communicator can dynamically modify the corresponding parameters of the valve positioner with relevant instructions, which changes the traditional parameter setting or modification method. The Bluetooth module in the valve positioner is set to passive link mode. After the device is started, the valve positioner will periodically collect the valve position value and store it in the buffer of the device. When the Bluetooth communicator searches for the valve positioner The valve positioner sends a link command. After establishing the link, the Bluetooth Communicator will obtain a link handle. After that, it enters the monitoring interface as shown in Figure 5, and can perform the three functions of reading the valve position value, valve position upper limit, and writing upper limit. When each function is executed, a control command is sent by the handheld communicator. The command is sent to the Bluetooth module from the serial port, including the Bluetooth link handle, function code (0x01-0x03 for the above three functions) and CRC check. area. After receiving the control instruction, the valve positioner first judges the link handle, judges whether to receive the instruction, and then executes the corresponding tasks respectively according to the function codes. Figure 5 shows the valve position value of the valve positioner read through the Bluetooth Communicator. In addition, the Bluetooth handheld operator can also operate Bluetooth electromagnetic flowmeters, Bluetooth temperature transmitters and other devices.

5 Conclusion

Field tests show that the Bluetooth module designed in this paper has stable performance, convenient use, strong practicability, and has certain anti-interference ability. It can also be upgraded according to needs, and can be effectively embedded in field devices instead of cables for wireless communication. The extension of the traditional wired industrial control bus provides a new networking method for the industrial monitoring network.

The author of this article is innovative: the Bluetooth wireless communication module is designed using BlueCore2-External Bluetooth chip, FB2520 band-pass filter and balun, LTCC ceramic antenna, etc., and is actually used in the Bluetooth handheld operator and valve positioner The results show that the Bluetooth module has stable performance and strong practicability.

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