Design scheme of wireless communication and intelligent chest strap
With the advancement of technology and the improvement of living standards, clothing should have more functions in addition to the insulation function, and with the increasing emphasis on personal health and sports, there have been many various home medical monitoring products and fitness products. Although these monitoring products improve people's quality of life, they also have deficiencies, such as: the product function is relatively simple; continuous long-term monitoring is not possible, or excessive user involvement is required; it is inconvenient to carry around or hinder people's normal life. If the sensors in some instruments for monitoring the human body can be miniaturized and wearable, various physiological signals of the human body can be collected through close-fitting clothing or chest straps and electronically driven and software-controlled, and the physiological conditions of the human body can be detected at any time, such as real-time Control illness or make exercise plans.
As a result, an intelligent chest strap was produced, and the human physiological parameter collection and wireless transmission system belonged to biological telemetry technology. The so-called biological telemetry refers to the collection and monitoring of biological parameters such as blood pressure, blood flow and temperature of a living body through wired or wireless methods within a certain distance (tens to hundreds of meters or even further).
1 The concept and implementation of smart clothing
The intelligent function of smart clothing is mainly achieved through the following ways:
(1) Weave intelligent fibers with sense and reaction function with ordinary fibers or weave intelligent fibers into ordinary fiber fabrics, and use this fabric containing intelligent fibers to make intelligent clothing;
(2) Modify the ordinary fiber to make it have the performance of intelligent fiber, and then use this fabric to make clothing;
(3) Combine some special substances into the fabric by dyeing and finishing to make the ordinary fabric have intelligent characteristics, and then make it into clothing;
(4) Combining ordinary clothing and external components to make smart clothing. These additional components include ordinary components and high-tech sensors, detectors, alarms, etc.
Therefore, smart clothing is roughly divided into two categories. The first is to improve the clothing materials, through chemical and physical means to change the structure of textile materials, so that it has the functions that ordinary materials do not have. The other can be simply understood as informational clothing, that is, by embedding various microchips, sensors and other devices in the clothing, the clothing becomes a wearable computer, which can interact with the human body in real time and receive commands from the wearer Or measure information about the human body itself.
2 Application and status of smart clothing and chest strap
As a modern person who pays more attention to health, he pays more and more attention to his physical health, and it is crucial to understand his physiological state conveniently and quickly. Therefore, it is very necessary for the design and research of the human physiological collection and wireless transmission system of the intelligent chest strap, which has important social significance. The application field of smart clothing is very broad, and the needs of military industry have become a main reason for the rapid development of smart textiles. In terms of civilian use, smart textiles also have huge potential for development, such as multi-functional sportswear and safety clothing for real-time detection of human physiological indicators. Multiple sensors or other medical equipment can be placed on the patient to detect the patient's signs; deploying a sensor network at home can help the elderly, especially more and more elderly people over the age of 60 in the world get better at home Take care and help them detect the disease as soon as possible.
At present, more advanced smart chest straps have been developed abroad, and New Zealand Zephyr Technology has recently developed a biological smart chest strap. As long as people wear this biological chest strap on their body, it will collect information such as the heartbeat, body temperature, body posture, movements and breathing rate of the human body. Scientists at the Material Research and Innovation Center at Bolton University in the UK have recently developed a smart bra that can detect early breast cancer. The domestic research on the development of smart clothing originated in the late 1970s. At that time, electronic technology was still relatively backward, so the development of smart clothing was also very slow, mainly used in special industries such as aerospace.
The development of intelligent chest strap collection of human physiological parameters has great potential, mainly in the following directions:
(1) Using the Internet and advanced sensor technology to make telemedicine more popular.
(2) The secondary development of medical instruments enables the old instruments to directly use the computer network to monitor human physiological parameters.
(3) Using advanced technology to improve the accuracy of human physiological parameter data collection.
(4) Develop portable multi-channel biological telemetry system.
(5) Real-time collection, wireless transmission and monitoring of human physiological parameters.
3 R & D of smart chest strap
With the development of science and technology, the intersection and penetration of clothing majors and other disciplines, and the advancement of biomedical disciplines, there will be a new development in the collection of various physiological parameters and wireless transmission instruments for intelligent chest straps.
The traditional wired transmission method seriously affects the daily life and daily life. It is difficult to monitor anytime and anywhere. The mobility of the smart chest strap allows users to use it in free movement. It has reprogrammability, wireless communication capabilities, operation and interaction. Continuity and other characteristics, and the whole computer is integrated with the user, and can be moved arbitrarily with the wearer. The research and development of the smart chest strap is a branch of clothing functionality and comfort. It is based on the hardware system of the smart chest strap and performs hardware operations through software programming to achieve real-time physiological parameters of the human body, such as heart rate, pressure, temperature and humidity. Collect and transmit the measured data to the display device or computer by wireless transmission. In addition, it can realize the visualization function. The database in the background can realize the instant viewing and storage of the data.
3.1 Selection of sensors
In the traditional analog signal wireless transmission acquisition system, it is necessary to solve the technical problems such as lead error compensation, multi-point measurement switching error and zero drift error of the amplifier circuit in order to achieve high measurement accuracy. In addition, the electromagnetic environment of the monitoring site is generally harsh, various interference signals are strong, and the simulated temperature signal is easily interfered to produce measurement errors, which affects the measurement accuracy. Therefore, in the acquisition system, the use of a new digital temperature sensor with strong anti-interference ability is the most effective solution to these problems. Considering the economics of the system and the advantages, disadvantages and development status of the sensor, it is determined that the temperature sensor is digital, pressure and humidity The sensor adopts voltage integrated type.
3.2 Determination of the radio frequency chip
Through the understanding and mastering of the working principle and interface technology of the single chip microcomputer, through the research on the wireless radio frequency module on the market, a suitable chip is selected, that is: with a wireless transceiver; containing 8051 controller and A / D conversion function; Can work under low voltage; there is a voltage regulator inside; few peripheral devices are needed; the design is simple. The RF transceiver chip nRF24E1 with the above functions can be used as the main chip of the parameter acquisition hardware system.
3.3 Study of chest strap
Because it is a parameter acquisition system for intelligent chest straps, corresponding research on the materials and styles of chest straps can enable the development of this system to avoid normal operation due to chest straps. For medical or sports-specific intelligent chests The design of the chest strap style and material needs to be more concise, especially the research on the style to make it easy to wear, different from the traditional chest strap, and make the style, material and software and hardware system well. Combined to make it one and finally reach the state of man-machine integration.
3.4 Technical realization of parameter collection and wireless transmission
According to the advantages and disadvantages of each software developed for the single-chip program, according to the pin description of the main device, the program is written to control the port, and the human body parameter collection through the sensor is realized (using the μVision 2 compiler). Then, the data is wirelessly transmitted according to the written program, and displayed by the display.
The radio frequency connection must be able to guarantee a 64 Kb / s data rate in both directions, and requires that the connection is full duplex, that is, both transceivers can work simultaneously. Due to the ShockBurst feature, all protocol-related operations are handled by hardware. Although nRF24E1 uses a low-speed 8051 microcontroller, the wireless transmission speed can reach 1 Mb / s. After initial configuration, nRF24E1 can control the RF transceiver. The master-slave transceiver must be synchronized before data transmission. The data packet used by RF can be set to 248 b (8 b pilot signal +16 b CRC + 32 b address +24 B useful data), therefore, each data contains There are 24 sampled signals. In order to meet the real-time requirements, it must be sent once every 3 ms.
The design of the radio frequency antenna is: the antenna is laid on a printed board with a thickness of 1.6 mm and a material of FR4, and a 1/4 wavelength monopole antenna is used. The dielectric constant of the FR4 sheet at 2.4 GHz is 4.4, and the width of the monopole antenna W = 1.5 mm. Under these conditions, the dielectric constant of the material around the monopole antenna is calculated to be 3.16, so that the wavelength under this condition can be calculated. It is 6.89 cm, and the 1/4 wavelength is 1.72 cm. But the antenna is placed on the printed board. In order to make it easier to resonate at 2.4 GHz, the length needs to be increased by 5 mm. Finally, its antenna is shaped like a wire with a length of 22 mm and a width of 1.5 mm on the printed board.
3.5 System development
Use visual language development to establish a human-computer interaction interface. Among them, the visualization environment has interface technology, which can realize the serial communication between the PC and the hardware system, and can be connected to the database to realize the collected data display, query, storage, and update functions. As shown in Figure 1, Figure 2. 
4 Conclusion
The data obtained by the collection system can play an auxiliary role in people's daily life, can help medical staff to better grasp the physical condition of patients, and can also be used to help coaches or health care providers guide athletes to develop a reasonable training plan to avoid athlete training. It is unreasonable; it can also help clothing designers to combine some physiological factors of the human body in the design, more humane and scientific design of clothing styles, and choose clothing materials that are more suitable for the human body.
The 21st century is an era of global informatization. Wearable electronic smart clothing will undoubtedly represent the trend of future functional clothing development. At present, China has just started its research on smart clothing. Compared with developed countries, there is still a gap. Only by continuously developing new functional clothing products can we have a place in the world of smart clothing.
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