Design of portable exercise volume and physiological parameter monitor based on MSP430

With the rapid development of my country's economy and medical and health care, people are paying more and more attention to their health status, and their health concept has gradually changed from simply "preventing diseases" to "improving and promoting health" - that is, from the secondary prevention of "early detection, early diagnosis, and early treatment" to the primary prevention of "using various health promotion methods to improve health status". In line with this, intelligent monitoring instruments, as an important means of health management and promotion, have become an emerging application field and an important market. Everyone can "manage their health" through certain health promotion methods. The portable exercise volume and physiological parameter monitor described in this article is an intelligent instrument that can be used for personal health management. Its design concept and application background fully reflect the basic development trend of my country's emerging health management industry.

System Design

The portable exercise volume and physiological parameter monitor can record and monitor the human body's exercise data in real time, and quantitatively evaluate the human body's exercise volume and physical energy consumption, and display it in real time in the form of calories; the monitor can also monitor the human body's blood oxygen saturation, ECG signal, heart rate, body temperature and other important physiological parameters in real time, and evaluate whether the exercise in physical exercise or rehabilitation training is excessive from the two aspects of exercise volume and physiological parameters, and decide whether to issue an alarm prompt based on whether the exercise volume and physiological parameter values ​​are within the safe range. Therefore, the monitor can not only ensure the effect of exercise, but also effectively prevent accidents caused by "excessive exercise".

As shown in Figure 1, the portable physical activity and physiological parameter monitor is a typical single-chip microcomputer application system. In the system design, attention should be paid to meeting the requirements of micro-power consumption, miniaturization and reliability. The field usability of the portable physical activity and physiological parameter monitor requires that its current consumption is small in order to reduce the power consumption of the system and extend the battery life. Therefore, micro-power design is an important part of system design. The core of micro-power design is the design of the minimum power consumption system, which can not only reduce the power consumption of the system, but also make the system have lower electromagnetic radiation and higher reliability. The micro-power design of this monitor specifically includes system operation power consumption analysis, low power design, power management and low power software design.

Specifically, portable exercise volume and physiological parameter monitors must meet the following requirements:

● Capable of collecting and storing the human body’s motion signals and physiological signals with high precision, and processing the data accordingly through relevant algorithms;

● It has a friendly Chinese human-machine interface, which enables easy setting and operation;

● It can conveniently exchange data with a PC, and can perform subsequent data analysis and processing through the supporting software on the PC;

● The monitor can be conveniently worn on the human body, is light in weight, small in size, and powered by 1 to 2 batteries.

As shown in Figure 1, the motion sensor, digital blood oxygen module, ECG module and signal conditioning unit constitute the forward channel in the system. The human motion data and data of physiological parameters such as blood oxygen saturation, ECG, heart rate, etc. enter the central control unit through the forward channel.

The central control unit uses the ultra-low power 16-bit microcontroller MSP430F149 (hereinafter referred to as F149), which integrates an 8-channel 12-bit precision A/D conversion module, 60kB FLASH ROM and 2kB data RAM, and has a hardware multiplier and 2 serial communication interfaces. Using F149 as the central control unit of this system can realize the collection, reception and processing of motion signals and various physiological signals without the need for an external A/D chip. It improves the advancement, reliability and integration of the system, can effectively reduce the difficulty of system design, and greatly improves the overall performance of the system.

The data storage unit is used to store motion data, blood oxygen saturation, ECG signals and other data within the system. It is necessary to select a suitable data storage chip based on requirements such as storage capacity, power consumption, interface form, access speed, and volume.

The display and keyboard interface unit provides a keyboard interface for setting up and operating the monitor, and realizes Chinese character function menu display, numerical display of physiological parameters and waveform playback through graphic dot matrix LCD, providing the system with a friendly and intelligent human-computer interaction interface.

The clock unit provides the system with real-time time coordinates, which in turn can provide reference start and end time points for data storage.

The data communication unit provides a means of data exchange between the monitor and the PC, which can be either a wired interface such as serial, USB, TCP/IP network communication, or a wireless communication network with a fixed frequency (such as 433MHz) can be established through a wireless transceiver chip, or a long-distance wireless transmission network based on GPRS. [page]

The power supply unit supplies power to the analog and digital circuit parts of the monitor respectively, provides different operating voltages and certain power partition management functions, and its output quality is directly related to the accuracy and reliability of the system.

Motion monitoring module

The motion monitoring module completes the input, amplification and filtering of human motion signals, and mainly includes motion sensors and signal conditioning units.

Motion sensors can generally be in two forms: one-dimensional vibration sensors and three-dimensional motion sensors. The former, such as micro-vibration sensors, are active, low-power vibration detection devices that generally output in the form of sine waves, which can be converted into pulse waveforms and input into microcontrollers. The microcontroller records the number of steps of the runner in real time by detecting high levels, and uses this to calculate the physical energy loss of the runner.

More accurate human motion signals can be obtained through three-dimensional acceleration sensors. As motion sensors that have only been developed and mature in the past decade, acceleration sensors can not only evaluate the amount of exercise by measuring the energy consumption of exercise, but also reflect the intensity and frequency of human motion by measuring acceleration, and can convert various motion states of the human body into voltage signals of different amplitudes. It is easy to install, small in size, and simple to measure. The three-dimensional acceleration sensor is an ideal motion sensor element in the forward channel of this monitor.

As shown in Figure 1, the function of the signal conditioning unit is to amplify or adjust the weak electrical signal (usually a voltage signal) output by the sensor without distortion to a voltage signal with sufficient amplitude that can be directly sampled by the A/D conversion module, and the impact of the signal conditioning unit on its preceding sensor and subsequent A/D conversion module should be as small as possible.

The signal conditioning unit specifically includes a signal amplification circuit, a filtering circuit, and a precision voltage reference circuit, etc., which mainly realize functions such as signal amplification, shaping, and filtering. The signal amplification circuit in the signal conditioning unit should have strong common-mode rejection and differential amplification capabilities, relatively high actual common-mode rejection, large input impedance, and small offset and temperature drift, which can effectively reduce the impact of the signal amplification circuit on the sensor input signal and reduce temperature errors. At the same time, the filter in the signal conditioning unit should use a precision op amp with a co-phase structure and an RC network to form a high-order active filter, which can not only provide a certain gain and buffering effect, but also reduce the impact on the subsequent stage, especially the A/D conversion.

The signal conditioning unit is the main part of the analog circuit in this monitor. The accuracy of the adjusted signal directly determines the accuracy of the human motion signal that can be collected in the system. Its circuit structure and complexity are also directly related to the overall power consumption and volume of the system. Therefore, the design of the signal conditioning unit must meet the requirements of micro-power consumption and miniaturization design, be able to work under a single power supply, and its signal amplification range must be consistent with the signal amplitude required for A/D conversion. The circuit structure should be simple and highly integrated, and it is not advisable to use a design with too many discrete components.

Physiological parameter monitoring module

From the perspective of overall system design and reducing the difficulty of design, important physiological parameters of the human body such as blood oxygen saturation, ECG signal, heart rate, body temperature, etc. can be directly obtained through some existing functional modules on the market without having to design them by themselves. For example, there are integrated functional modules (referred to as digital blood oxygen modules) for monitoring blood oxygen saturation, heart rate, etc. for secondary development on the market, which often have integrated signal processing cores (such as Dolphin's OEM-701 module). This digital blood oxygen module can directly detect human blood oxygen saturation, heart rate, body temperature and other data through the probe, and supports the output mode of the serial interface.
Since the detection circuit of the ECG signal is generally more complicated, the functional modules of ECG signal detection available on the market can also be used for secondary development. Specifically, the BT007 seven-channel ECG module can output synchronous seven-channel ECG waves, has four-level programmable gain, three-level filtering mode (diagnosis mode, monitoring mode and surgical mode), has pacing pulse suppression function and lead-off alarm function, and the ECG signal results detected can also be output through the serial interface.

The central control unit F149 microcontroller of this monitor contains two serial communication interfaces - USART0 and USART1, so it can directly receive the blood oxygen saturation, heart rate and ECG signal data output by the digital blood oxygen module and ECG module. This design idea of ​​directly using existing integrated functional modules for secondary development can effectively reduce the design difficulty of this system and improve the system integration.

Data storage unit

Since the monitor needs to store a large amount of field data, the requirements for data storage capacity are very high, and EEPROM, SRAM, etc. with low storage density cannot meet the requirements. The interface level of ATMEL's AT45 series SPI serial interface FLASH memory matches F149, and can be directly connected in hardware. The use of SPI serial three-wire interface reduces the I/O resource occupation, can effectively reduce the space occupied by the system, improve system reliability, and reduce switching noise. The AT45 series memory chip also includes 2 SRAM type data buffers, and the capacity of each buffer is the same as the storage capacity of a page in the main memory array. In this way, data can be received even when the memory is being burned, which provides hardware guarantee for the real-time and reliability of data storage.

Parallel FLASH memory can also be used in this monitor, such as Samsung Electronics' K9xxGxxxxM series NAND FLASH chip, which can provide 4224M-bit storage capacity. This high storage density, large capacity parallel FLASH data storage chip is particularly suitable for the application environment where the system needs to store a large amount of real-time motion data and physiological data.

Data storage program

When designing the data storage program, we should focus on the requirements of micro power consumption and real-time performance. That is, the data storage program should be based on the interrupt program structure, and the A/D interrupt service subroutine is used to collect and store the three-dimensional motion data from the motion monitoring module in real time, and the two serial communication receiving interrupt service subroutines are used to receive and store the physiological data such as blood oxygen saturation, heart rate, body temperature and ECG signals from the blood oxygen module and ECG module respectively. These motion and physiological data are first placed in the 2KB data RAM of the F149 microcontroller, and then stored in the FLASH data storage chip by page writing.

Since the three-dimensional motion data from the motion monitoring module is a large amount of multi-channel, continuously changing data, considering the micro-power consumption and real-time requirements in the data acquisition process, it is more appropriate to use the sequence channel single conversion mode for the A/D conversion module of F149, which has simple timing control and high flexibility. At the same time, the Timer_A timer is used to time the A/D conversion module, so that it works in the count-up mode, and its timing time corresponds to the sampling frequency.

The serial communication receiving subroutine for receiving physiological data is also based on the interrupt response mode. The 32768Hz clock crystal oscillator provides the clock signal source for serial communication. The received blood oxygen saturation, heart rate, body temperature and ECG data are filled into the system's data RAM through two serial communication receiving interrupt response subroutines.

When using FLASH data storage chips to store large amounts of data of different categories in this system, it is necessary to pay attention to the division of the data buffer in F149 and the division of different data areas in the data storage chip. At the same time, several important variables need to be maintained in the main program of the system: such as a global variable that records the page number to determine the page to be accessed when reading and writing data; and a variable for the buffer flag, so that the program can determine whether the current buffer is full, whether it needs to be switched, and which buffer to switch to based on the flag.

In addition, when writing the data writing subroutine of the FLASH chip, attention should be paid to the timing coordination between data acquisition, reception and data storage to ensure the continuity of data acquisition and reception and the non-loss of data. At the same time, a stable clock signal should also be given priority in the process of data reading and writing, which is often overlooked by designers.

The specific data storage program flow is shown in Figure 2.

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Working mode and process of the monitor

Portable exercise volume and physiological parameter monitors have two main working modes: sports field mode and medical monitoring mode.

In the sports scene mode, the system completes the collection and storage of human motion data and physiological data (blood oxygen saturation, heart rate, body temperature, ECG signal, etc.) at the sports scene, calculates the value of the accumulated exercise volume, and determines whether to give an alarm prompt based on whether the exercise volume is excessive and whether the physiological data is within the safe range. At the same time, the data stored in the monitor can also be transmitted to the PC for subsequent processing, such as providing an analysis report of the exercise process and database management of all data during the exercise process.

In the medical monitoring mode, the motion monitoring module of the monitor is mainly used to perceive the patient's posture. The system focuses on continuous real-time monitoring of the main physiological parameters of bedridden patients, and can perform remote data transmission and remote alarm through the supporting software of the connected microcomputer. This working mode of the monitor is very suitable for home care of long-term bedridden patients, and implements long-distance real-time monitoring of their vital signs away from the hospital.

The specific threshold range of exercise volume and physiological parameters in this system should be determined in combination with the specific theory of sports medicine and through certain human exercise grouping experiments. The control program of the monitor needs to complete the quantitative calculation of exercise volume, the perception of the athlete's posture, and the intelligent judgment of exercise volume and physiological parameters, and issue an alarm when the exercise is excessive or the physiological parameter indicators are abnormal.

Conclusion

The portable exercise volume and physiological parameter monitor can complete the functions of evaluating exercise energy consumption, evaluating exercise risk factors and exercise intervention management during exercise, so as to greatly improve exercise efficiency and safety. At the same time, the monitor can also be used for medical monitoring and home care. It is an intelligent instrument dedicated to personal health management services and has a foreseeable broad market prospect. The design scheme in this paper has achieved good results in the process of prototype implementation.