Application of Bluetooth technology in sensor wireless network

Usually in the measurement and control system, sensors are important devices for information collection. Data collection depends entirely on sensors. How to realize the networking of sensors, which are known as "nerve antennae", is also a hot research issue. In most current measurement and control systems, sensors are mostly wired, but in some special cases, wired cable connections will obviously cause a lot of inconvenience and cannot meet actual needs. With the development of emerging wireless technologies (such as Bluetooth technology) and the reduction of chip prices, wireless methods have been used in many occasions to replace the original wired interface methods. Wireless networked sensors are bound to become an important direction for the development of sensors. Based on the introduction of IEEE1451.2 and Bluetooth technology, this paper proposes a wireless networked sensor structure model based on the Bluetooth protocol, and focuses on the implementation of the simulation experimental device developed based on this model and its application in remote patient monitoring.

1 Wireless network sensors based on IEEE1451.2 and Bluetooth protocols

1.1 IEEE1451.2 Standard

IEEE1451.2 is a standard for intelligent sensor interface modules. It provides an interface standard for networking sensors and transmitters. It uses a universal A/D or D/A converter as the I/O interface of the sensor, converts various sensor analog quantities into data in the standard format, and connects a small memory, the transducer electronic data sheet (TEDS), to the processor target model specified in the standard, the network adapter (NCAP, network capable application process). In this way, the data can be connected to the network according to the protocol specified by the network. The structural model of this standard provides a 10-wire standard interface connecting the smart transducer interface model (STIM, smart transducer interface module) and NCAP, the transducer independence interface (TII, transducer independence interface). Its workflow is that the analog signal output by the sensitive element is converted by A/D and processed accordingly (filtering, calibration), and then encapsulated into a data frame by the network processing device according to the program settings and network protocol (TCP/IP), and transmitted to the network through the network interface.

1.2 Bluetooth Technology

As a new short-range wireless communication protocol, Bluetooth technology provides an open standard for wireless data and voice communication. It has many unique advantages: strong portability and can be applied to a variety of communication occasions; simple hardware integrated circuit application, low cost, easy to implement, and easy to promote; Bluetooth has low power consumption and little harm to the human body; Bluetooth uses spread spectrum frequency hopping technology, has strong anti-interference ability, and increases the security of information transmission. Bluetooth technology is attracting widespread attention from many experts and scholars with its unique advantages.

1.3 Sensor structure model

The structure model of wired networked sensor based on IEEE1451.2 includes three parts: STIM, TII and NCAP. The wireless networked sensor designed in this paper based on IEEE1451.2 and Bluetooth protocol uses Bluetooth module instead of TII to achieve wireless connection, which is similar to the mode of realizing a wireless STIM and wireless NCAP receiving terminal. They communicate with each other in a master-slave mode in a point-to-multipoint manner in the Bluetooth Peak network.

STIM accesses Ethernet or In2ternet through wireless NCAP, and NCAP is connected to the network through the assigned IP address, as shown in Figure 1. Compared with the typical wired method, the above wireless network model adds two Bluetooth modules. For the Bluetooth module part, the standard Bluetooth external interface circuit generally uses RS232 or USB interface, while TII is a serial interface that controls the STIM linked to it. Therefore, a Bluetooth circuit similar to the TII interface must be designed, and a special processor must be constructed to complete the functions of controlling STIM and converting data to the Bluetooth host control interface (HCI, host control interface). Interface modules can be used for hardware implementation, and standard STIM software modules can be used for software implementation: STIM module, STIM sensor interface module, TII module, TEDS module, and address and function module.

2 Implementation of simulation experimental device

The following uses the simulation device developed in the laboratory as an example to illustrate the implementation of the sensor. The structural block diagram of the device is shown in Figure 2. The MCU in the front-end wireless STIM is used to regularly collect the temperature value of the temperature sensor and transmit the data to the NCAP via the Bluetooth wireless network. The NCAP will store the value in a specific location. When a browser wants to view the value, the value will be embedded in the corresponding web page program, and the entire program will be encapsulated by TCP/IP and transmitted to the client's browser.

2.1 Implementation of STIM

The MCU used in STIM is AD's microconversion chip ADμC812. The chip has an 8052-compatible microprocessor that complies with the IEEE1451.2 standard. It uses the 640B data memory inside the chip ADμC812 as a rewritable TEDS storage, uses an internal 12-bit ADC to achieve A/D conversion, and communicates with the Bluetooth module through the UART serial port inside the chip. The Bluetooth module uses the Ericsson ROK101008 series that supports point-to-multipoint, and the module comes with a RF microstrip antenna. The internal structure of the ROK101008 Bluetooth module complies with the Bluetooth specification 1.1, and its internal baseband controller also provides a UART interface. The Bluetooth module provides a host controller interface (HCI) to implement a unified interface for accessing Bluetooth hardware. Combined with the RS232 serial port, data communication between the main controller and the host can be realized at the transport layer, and the baseband and radio frequency provide upper-layer links and services. At the same time, ADμC812 should also complete the initialization, data acquisition and processing of the temperature sensor.

(1) Temperature sensor DS18B20 interface and driver.

The temperature sensor is DS18B20, which is a one-line digital temperature sensor produced by DALLAS. It is mainly composed of 4 parts: 64-bit ROM, temperature sensor, non-volatile temperature alarm trigger TH and TL, and configuration register. The 64-bit serial number in the ROM is the address sequence code of the DS18B20. The function of the ROM is to make each DS18B20 different, so that multiple DS18B20 can be connected to one bus. The host must go through 3 steps to control the DS18B20 to complete the temperature conversion: initialization, ROM operation instructions, and memory operation instructions. Its workflow is: initialization → ROM operation instructions → memory operation instructions → data transmission. The working sequence includes initialization timing, write timing and read timing. When operating, you must first start the DS18B20 to start the conversion, and then read the temperature conversion value. Its hardware interface is shown in Figure 3.

(2) Initialization of Bluetooth module ROK101008.

When the Bluetooth module is powered on, it will complete the initialization work so that it can establish a connection channel with the Bluetooth within the signal range. This process is mainly completed by the MCU sending HCI instructions to the Bluetooth module. HCI instructions include instruction grouping, data grouping and event grouping. The specific format is: operation code + total parameter length + parameter 0 + parameter N.

The following is the HCI instruction for implementing ACL data connection between master and slave devices (the character corresponds to the instruction's opcode, which consists of the first 10 bits and the last 6 bits, and the parameters of the instruction are in brackets): After the slave device is powered on, the inquiry is enabled and reset Write_scan_enable (0x03). The master device sends 0x00000000000, then the HCI instruction for establishing ACL connection is Create_Connection (0x000000000000, 0x18, 0, 0, 0, 0), and the slave device receives the connection request instruction Accept_connection_request (0x111111111111, 0), assuming that the master device address is 0x111111111111. In this way, the ACL data connection is established between the master and slave devices. For example, the corresponding opcode for Inquiry is x0001, 0x01. For specific HCI instructions, please refer to the Bluetooth specification.

2.2 Implementation of NCAP

The function of NCAP is to realize the access of Bluetooth module to Ethernet (Ether2net). ROK101008 series Bluetooth module is also selected, so that multiple STIMs can be connected to the same NCAP. The 8-bit microprocessor W77E58 and TCP/IP protocol stack chip W3100A are used together to realize the network interface for access to Ethernet (Ethernet).

(1) Protocol stack chip W3100A is initialized.

W3100A is a TCP/IP protocol stack chip, which includes the following protocol layers: TCP, IP, UDP, ICMP, Ethernet protocol data link DLC and MAC protocol. Its working mode is similar to Windows's SoketAPI. To facilitate access to sensors, sensors can be designed to have Web server functions. W3100A supports full-duplex mode, has a dual-port SRAM data buffer inside, and is packaged in a 64-pin LQFP. It provides parallel and serial ports to communicate with the MCU. The hardware interface of MCU and W3100A is shown in Figure 4. Among them, the RTL8201 chip is the selected device for the Ethernet physical layer.

W3100A provides MII interface to connect to RTL8201, where pins RX_CLK, RXDV, RXD[0∶3] and COL are used for data reception, and TX_CLK, TXE, TXD[0∶3] are used for data transmission.

The MCU provides an analog I2C interface to communicate with W3100A.

The chip W3100A must be initialized for normal operation. Initialization mainly involves setting the necessary registers, including: gateway address register GAR, subnet mask register SMR, hardware address register SHAR, and IP address register SIPR. After the above registers are set, the chip is activated by executing bit 0 Sys_init of the control register CR.

(2) Implementation of WEB service functions.

The protocol stack chip W3100A implements the TCP/IP protocol in hardware, so it is obviously easier to integrate the Web service function into the device, that is, the corresponding HTTP protocol should be implemented on the wireless NCAP, and the NCAP is equivalent to a "gateway" in terms of network function. To achieve remote browser and sensor interaction, the E2PROM (FM24C04) added to the sensor NCAP can be used to store the corresponding web page files. During interaction, HTTP determines which resources the sensor should provide to the browser through the uniform resource locator URL (uniformresourcelocator).

The web page file is stored in the FM24C04 in the sensor. When the browser of the monitoring center sends a page request, the processor on the NCAP embeds the monitoring value from the STIM end into the special mark in the corresponding web page file during TCP packaging, and then adds the corresponding HTTP header to the web page file and returns it to the requesting user, so that the user can see the actual monitoring value on the browser. Therefore, to realize the Web function, the HTTP protocol must be completed on the NCAP in terms of software, and an E2PROM (FM24C04) is added in hardware.

3 Application of simulation devices in patient monitoring systems

When the above networked sensor (experimental device) is used in patient monitoring, the patient can collect and detect a signal through the sensor carried on his body in a remote place (such as home), and the sensor transmits the signal to the monitoring center through Ethernet or Internet. The schematic diagram of the patient remote monitoring system is shown in Figure 5.

Utilizing the WEB function in the simulation device, this solution uses the B/S (browser/server) method to achieve remote monitoring center PC access to the sensor. This can minimize the requirements for the monitoring center PC and eliminate the need for client software design. The monitoring PC can easily query and monitor the sensor information through its browser (such as IE). The following is a simple dynamic web page program stored in the temperature sensor, in which the "@" is used to insert the temperature mark in the web page, and the web page file is stored in the E2PROM in the sensor. When the browser of the monitoring center sends a page request, the processor on the NCAP embeds the monitoring value from the STIM end into the "@" in the corresponding web page file during TCP packaging, and then adds the corresponding HTTP header to the web page file and returns it to the requesting user, so that the user can see the actual monitoring value on the browser.

4 Conclusion

The wireless network sensor design based on Bluetooth protocol proposed in this paper has safe and reliable information transmission and strong feasibility. Its special advantage of wireless can meet the needs of certain special situations and has broad application prospects and good market value. If the developed simulation experimental device is further verified and improved through clinical practice, it can be used in the patient remote monitoring system to realize real-time detection, monitoring, recording and storage of human body temperature. If blood pressure, heart rate and other sensors are added on this basis, the monitoring and recording of human blood pressure, heart rate and other parameters can be realized.