Design of cardiopulmonary auscultation skills training system based on single chip microcomputer

With the development of society, the reform of the medical system, the media's publicity, the people's legal awareness has been greatly strengthened, and a series of medical regulations have been introduced, further clarifying the rights and interests of patients. Patients, the main body of traditional medical teaching, have more often chosen to refuse to cooperate with teaching work.

In recent years, the increase in medical disputes and the tension in doctor-patient relationships have led to the continuous weakening of hospital teaching performance for the sake of their own interests. The conventional model of clinical medical education in medical schools 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. Introducing "simulation teaching" into the on-campus teaching process, a new clinical medicine teaching model of "theoretical teaching + single skill training - simulation teaching - clinical internship" is formed. The system has a simple structure and reproduces the working scenes of clinical medicine through model people, providing learners with a risk-free condition and environment for learning clinical knowledge and skills.

1 System structure

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 heart and lung 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

From the functional aspect, the system can be divided into six parts: voice playback unit, multi-channel analog switch, location recognition switch, wireless communication unit, power supply and low power design unit. The internal system block diagram of the model is shown in Figure 1.

Figure 1 Internal structure of the model person

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

Figure 2 Remote control system block diagram [page]

2.1 Selection of main controller chip

The main controller is the core of the whole system. The choice of the main controller chip is related to whether the whole system function can be realized or not. 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 convenient debugging. Taking the above factors into consideration, the main control chip uses MSP430 produced by Texas Instruments (TI). Because the system is a portable cardiopulmonary auscultation system, it is battery-powered, so it must be ultra-low power consumption to meet the requirements of medical teaching. The biggest feature of this chip is low power consumption. The voltage preparation 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 turned off;

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 features;

16-bit timer with 7-way capture and compare registers with mapping registers, Timer B;

16-bit timer with 3 capture/compare registers, Timer A;

On-chip comparator;

Serial online programming, no external programming voltage required, safety fuse protects program code;

Contains 60 KB flash memory and 2 KB random access memory.

2.2 Voice Playback

Voice playback is one of the important functions 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 occupies a large 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 level and price are slightly better than the famous ISD circuit, and it also has 21 kHz high-fidelity sound quality. The chip consists of a dedicated voice single-chip microcomputer and a FLASH RAM memory set. It has both a multi-segment voice playback function of 13~100 s and the intelligent characteristics of single-chip programmable. The chip has the following characteristics:

Storable sound length: 13~100 s;

Wide range operating voltage: DC 3~ 6 V;

Working current 50 mA, static current 1 A;

Directly drives 80.5W speakers, with two audio output modes: PWM and DAC;

Wide range sampling frequency: 4.8~21kHz;

The recorded voice can be divided into 1~8 parallel segments and 128 serial segments;

It comes with 8 input ports and 9 output ports, and the functions can be customized by the user;

FLASH RAM structure, can be repeatedly erased and written, life span is more than 10,000 times;

Two packaging types: COB28 and COB16;

The computer software used for development is super-intelligent and fool-proof graphic design, which can be used by laymen;

With the programming software, various control modes such as parallel, serial, and intelligent can be developed;

The peripheral circuit of the minimum system only needs one oscillation resistor and one power supply filter capacitor;

There are multiple time levels to choose from: 13 s/ 20 s/ 50 s/ 100 s;

After completing development and trial production, the mask can be put into production directly using the source file, and the sound quality and functional performance remain unchanged.

2.3 Multi-channel 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, the multi-way analog switch can only be used to select each speaker to be connected. The MAX306CPI chip is a 16-bit multi-way selection switch. 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.

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2.4 Design of wireless module

The design of wireless module includes two parts: hardware design and software design. Hardware design mainly includes PCB layout and antenna design, while software design mainly includes the definition of communication protocol.

Wireless modules operate in the ISM (Industrial Scientific Medical) ultra-high frequency band, which places higher requirements on the layout of the PCB. Generally speaking, 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 as much as possible, so that a large area of ​​copper can be applied on the other side of the PCB 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 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 generator polynomial. The sender generates the CRC codeword by generating g(x). The receiver divides the received codeword polynomial with the generator polynomial g(x). If the result is exactly the same, it means the reception is correct.

2.5 Power module

In the design of portable products, low power consumption design has always been a top priority in order to avoid frequent battery replacement and extend the product's usage time.

The power module is mainly used to manage the battery pack and supply power to other modules of the system. The power module is mainly used on the remote control to supply the normal operation of each module of the remote control. This system adopts two batteries to supply power, 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 is 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 function as much as possible. In terms of software, the intermittent wake-up working mode can be adopted. 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. Only when the response signal is received will the module enter the working state. The intermittent wake-up method can greatly reduce the power consumption of the system.

3. Upper computer teaching software

The main controller transmits the position information of the mannequin to the host computer through the I/O port. The host computer controls the display of the host computer software interface according to the received position signal. It can display the position of auscultation, sound characteristics, relationship with breathing and sound waveform information. 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 host computer interface is shown in Figure 3.

Figure 3 Block diagram of the host computer interface

4 Conclusion

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

The advantage of this system is that the design is highly practical and stable because the system utilizes the ultra-low power consumption performance of MSP430. In addition, the chip has high computing speed, large RAM and FLASH space, expandable I/O port, compatibility with some external chips, and convenient debugging. 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 is not only of great practical significance for improving the level of medical simulation teaching in my country at this stage, but also has a good market prospect.