Design of cardiopulmonary auscultation skills training system based on MSP430

Introduction

In recent years, due to the severe medical situation, the teaching performance of medical schools has been continuously weakened; the requirements of hospitals for doctors have been continuously improved, and there is a disconnect between school education and hospital requirements. With the development of society, the reform of the medical system, the publicity of the media, the legal awareness of the people has been greatly strengthened, and a series of medical regulations have been introduced, which further clarified the rights and interests of patients. Patients, the main body of traditional medical teaching, have chosen to refuse to cooperate with teaching work. In recent years, the increase in medical disputes and the tension in the doctor-patient relationship have led to the continuous weakening of the teaching performance of hospitals for their own interests. The conventional model of medical schools in clinical medical education is: theoretical teaching + single skill training - internship - clinical internship. However, due to various reasons, internships cannot be carried out effectively, resulting in the formation of the teaching model of "theoretical teaching + single skill training". Based on the above reality, the embarrassing situation of teaching in medical schools urgently needs to be changed. Introduce "simulation teaching" into the on-campus teaching process to form a new clinical medicine teaching model of "theoretical teaching + single skill training - simulation teaching - clinical internship". The system has a simple structure and reproduces the working scenes of clinical medicine through model people, providing learners with conditions and environment for learning clinical knowledge and skills without risk.

1 System structure composition

From the structural point of view, the system can be divided into two parts: the model and the remote control. The model mainly has an internal wireless receiving device and a control device as well as a special device on the human body surface. The remote control has an LCD screen, a keyboard and related instructions. The examiner can easily send a command signal to the wireless receiving device inside the model. The wireless receiving device determines the type of disease based on the received command, thereby controlling what sound should be emitted at each position on the model. When the stethoscope touches the corresponding position on the model, the corresponding device will give a position signal to the control unit, and then the control unit will control the corresponding speaker to close through a multi-way analog switch to emit the cardiopulmonary auscultation sound at the point. The examinee transmits this sound to the human ear through the stethoscope, which completely simulates a real auscultation process. The examinee palpates the different positions of the model through the probe of the stethoscope, and auscultates various pathological characteristics at different positions through the stethoscope, thereby judging whether it is a certain disease, thereby achieving the purpose of teaching and training.

2 Functional composition of the system

In terms of function, the system can be divided into six parts: voice playback unit, multi-channel analog switch, position identification switch, wireless communication unit, power supply and low power design unit. The internal system block diagram of the model is shown in Figure 1.

The system block diagram of the remote control is shown in Figure 2.


2.1 Selection of the main controller chip

The main controller is the core part of the entire system. The selection of the main controller chip is related to the realization of the entire system function. This system needs to realize functions such as voice playback, wireless transceiver, multi-channel analog switch, low power consumption, and upper computer teaching. Therefore, the chip is required to have a high computing speed, a large RAM and FLASH space, an expandable IO port (such as I2C, SPI, etc.), compatible with some external chips (such as FLASH memory with SPI or some other chips), low power consumption, and easy debugging. Taking all the above factors into consideration, the main control chip is MSP430 produced by Texas Instruments (TI). Because the system is a portable cardiopulmonary auscultation system powered by batteries, it must have ultra-low power consumption to meet the requirements of medical teaching. The biggest feature of this chip is its low power consumption. The voltage in the ready working mode is 3.3 V, and the current is a few milliamperes during normal operation, which fully meets the system requirements. The chip has the following performance:

low voltage range: 1.8 ~ 3.6 V;
ultra-low power consumption: 1.3 mA in standard mode, 0.1 mA when RAM is closed;
low current: 7 mA at 32 kHz, 2.2 V, 250 mA at 1 MHz, 2.2 V;
5 node modes and wake up from wait mode within 6 ms;
16-bit RISC instruction structure and 125 ns instruction cycle;
12-bit A/D conversion and internal reference voltage, sample and hold, automatic scanning characteristics;
16-bit timer with 7-way capture and compare registers with mapping registers, timer B; 16-bit timer with 3-way capture/compare registers, timer A; on-chip comparator;
serial online programming, no external programming voltage required, safety fuse to protect program code;
contains 60 KB flash memory, 2 KB random access memory. [page]

2.2 Voice playback

Voice playback is one of the important components of this system. There are two problems to be solved here, one is the storage of voice data, and the other is the encoding, decoding and playback of voice. Since WAV waveform data takes up a lot of space, it is necessary to compress and encode the original data first. Therefore, the system uses the PM50 intelligent voice chip developed by Zhongqing Century Technology Company, which is both a voice playback circuit and an intelligent single-chip microcomputer. Its sound quality and price are slightly better than the famous ISD circuit, and it also has 21 kHz high-fidelity sound quality. The chip is composed of a dedicated voice microcontroller and a FLASH RAM memory. It has both a multi-segment voice playback function of 13 to 100 s and intelligent features programmable by the microcontroller. The chip has the following features:

It can store sound length: 13 to 100 s;
wide range of operating voltage: DC 3 to 6 V;
operating current 50 mA, static current 1 μA;
directly drive 8 Ω 0.5 W speakers, with PWM and DAC two audio output modes;
wide range of sampling frequency: 4.8 to 21 kHz;
the recorded voice can be divided into 1 to 8 parallel segments and 128 serial segments;
it has 8 input ports and 9 output ports, and the functions can be customized by the user;
FLASH RAM structure, can be repeatedly erased and recorded, with a lifespan of more than 10,000 times;
two packaging forms: COB28 and COB16;
the computer software used for development is a super-intelligent fool-proof graphic design that can be used by laymen;
with the programming software, it can develop a variety of control modes such as parallel, serial, and intelligent;
the peripheral circuit of the minimum system only needs an oscillating resistor and a power filter capacitor;
there are 13 s/20 s/50 s/100 s multiple time levels are optional;
after completing the development and test production, the source file is directly used to produce the mask, and the sound quality effect and functional performance remain unchanged.

2.3 Multi-way analog switch

The multi-way analog switch is mainly used to select the sound of the speaker at the playback position. Because the PM50 chip can only connect to one speaker, it can only be selected through the multi-way analog switch to connect each speaker. The MAX306CPI chip is a 16-bit multi-way selection switch. The two chips can be expanded to form a 32-way selection switch. The chip voltage is between 4.5 and 30 V, the power consumption is very small, and it does not affect the pronunciation of the speaker, which fully meets the requirements. And the stethoscope probe can easily touch the dedicated position under the skin of the model, so this technology is a good choice for this system.

2.4 Design of wireless module

The design of the wireless module includes two parts: hardware design and software design. The hardware design mainly includes the layout and routing of the PCB diagram and the antenna design. The software design is mainly the definition of the communication protocol.

The wireless module works in the ISM (Industrial Scientific Medical) ultra-high frequency band, which puts higher requirements on the layout of the PCB board. Generally speaking, the peripheral components should be as close to the wireless chip as possible, and all components should be arranged on the same side of the PCB board as much as possible, so that a large area of ​​copper can be applied on the other side of the PCB board to reduce interference. In terms of software, a good communication protocol is also one of the important guarantees for the stable operation of the wireless module. In addition to specifying the response relationship, error detection is also an important link in the communication protocol. The most commonly used error detection method at present is the cyclic redundancy check (CRC check), which is characterized by the fact that the length of the information field and the length field can be arbitrarily selected. The selection principle of the CRC code set is: if the code word length is N, the information field length is K, and the check field length is R, where N=K+R, then for any code word in the CRC code set, there is an R-order polynomial g(x) such that:

where: m(x) is the K-order information polynomial; r(x) is the R-1-order check polynomial; g(x) is the generating polynomial. The sender generates CRC codewords by generating g(x), and the receiver divides the received codeword polynomial by the generating polynomial g(x). If the result is divisible, it means that the reception is correct.

2.5 Power module

In the design of portable products, low power consumption design has always been a top priority to avoid frequent battery replacement and extend the product's single-use time. The power module is mainly used to manage the battery pack and power other modules of the system. The power cross block is mainly used in the remote control to supply the normal operation of each module of the remote control. This system is powered by two batteries and has a DC/DC power chip with buck-boost function. A good power module design can effectively improve the utilization efficiency of the battery, maintain a stable voltage, reduce power ripple, and increase the output current.

2.6 Low power design

Since this system is powered by two dry batteries, the system power consumption requirements are relatively high. In order to extend the battery life and avoid frequent battery replacement, low-power design requirements must be considered in all aspects of system design. Low-power design is to reduce the system clock frequency, power supply voltage and gate activity factors. From the hardware point of view, to reduce the power consumption of the system, it is necessary to choose low-power chips or chips with sleep functions as much as possible. In terms of software, intermittent wake-up can be used. If a functional module has a long idle time, it can be temporarily turned off or put in a low-power state, and then the response signal is detected by timed wake-up. The module will only enter the working state when the response signal is received. The power consumption of the system can be greatly reduced by intermittent wake-up.

3 Upper computer teaching software

The main controller transmits the position information of the model to the upper computer through the I/O port. The upper computer controls the display of the upper computer software interface according to the received position signal. It can display the position of the stethoscope, the characteristics of the sound, the relationship with breathing and the waveform information of the sound. In addition, an external speaker can be connected to amplify and play the heart and lung sounds heard to achieve the purpose of medical teaching. The
design block diagram of the upper computer interface is shown in Figure 3.


4 Conclusion

The rapid development and continuous expansion of the application scope of the MSP430 series microcontrollers mainly depend on the following characteristics: powerful processing power; the use of a reduced instruction set (RISC) structure; rich addressing modes; the concise 27 core instructions and the on-chip data memory can participate in multiple operations; efficient table lookup processing instructions; high processing speed, the instruction cycle is 125 ns under 8 MHz crystal drive. These characteristics ensure the compilation of efficient source programs. In addition, the MSP430 series microcontrollers have many interrupt sources, and can be arbitrarily nested, which is flexible and convenient to use. When the system is in power-saving standby mode, it takes only 6μs to wake up with an interrupt request.

The advantage of this system is that the design is highly practical and stable because it utilizes the ultra-low power consumption performance of MSP430. The chip has high computing speed, large RAM and FLASH space, expandable I/O ports, is compatible with some external chips, and is easy to debug. The system uses an ordinary stethoscope to test heart and lung sounds, which can more realistically simulate the real clinical environment. Therefore, the research and development of related technical products not only has important practical significance for improving the level of medical simulation teaching in China at this stage, but also has good market prospects.