基于单片机的心电监测系统设计-毕业论文.doc

1 introduction
The cardiovascular disease has become a threat to human health and life of one of the major diseases, heart disease mortality is still in the lead. According to statistics, about per year on average in the world, millions of people die of the disease in our country due to cardiovascular disease deaths accounted for about 44% of all deaths, a lot of heart patients is due to the failed to timely find out delayed treatment [1] and eventually lead to death. Therefore, the diagnosis of cardiovascular disease, prevention is the top issue facing the medical profession today. As soon as possible to find the cardiovascular system disease symptoms, timely understanding of the heart, to disease is of great significance to the prevention and treatment in time.
1.1 ecg monitoring system development background and significance
Heart is a vital organ of the human body, in the process of man's life, the heart constantly, shrinkage and expansion, to take blood from vein into the heart, and into the artery can realize the function of the pump. Heart before mechanical contraction, generate electricity excited in the first place. Tiny electric current can be produced by myocardial excited through body tissue conduction to the surface, to produce different at different positions of the body surface potentials. If two electrodes are placed in the body, with wire connection to the ECG monitoring system (that is, the precision of the galvanometer) at both ends, it will according to the time order of heart excited, record the potential difference between two points surface, forming a continuous curve, that is the electrocardiogram (ECG) [1]. Electrocardiogram (ecg) is inside the heart excited potential changes in the process of generation, transmission and recovery of synthetic waveform. It not only with a single curve of myocardial cell action potential is obviously different, and by measuring the position of the electrodes are placed and connection mode varies. Ecg signal is one of the earliest application in the medical human bioelectricity, now people can through the analysis and study of ecg signal related to cardiovascular disease to make prediction and diagnosis. Therefore, accurate and complete to ecg signal extraction in time, and provide effective means of auxiliary analysis and diagnosis is an important and meaningful research subject.
1.2 ecg monitoring system development present situation
At present, the domestic each big medical equipment factory and scientific research units in the development of ecg monitoring system invested a lot of resources, and have developed each has its characteristics of ecg monitoring system products. The rapid development of electronic technology and the mutual promotion of clinical medicine, there have been a variety of ecg monitoring products, common have bedside ecg monitoring, holter monitor ecg monitoring, phone and antenna ecg monitoring, etc.
1.2.1 bedside ecg monitoring
Bedside ecg monitoring is to be in bed guardian continuous or discontinuous ecg monitoring, it is the key content of cardiac monitoring. Since 1962 founded the coronary care unit, both at home and abroad has carried out the bedside ecg monitoring. At present, ecg monitoring is widely applied to the clinical monitoring of critical care and critical care, all kinds of surgery,
Special inspection and monitoring of treatment.
Due to the bedside ecg monitoring, to improve the level of clinical diagnosis and medical treatment quality, greatly improve the success rate of rescue critically ill patients, prevent and reduce the effect of medical malpractice or medical dispute, also reduce the labor intensity of medical staff, improve work efficiency.
1.2.2 holter monitoring
Dynamic electrocardiogram (ecg) is to use a tape or solid-state recorder 24 hours continuous record of the patient in the daily activities of ecg information, then playback and analysis by computer and edit print [2].
Dynamic ecg records the different status, different positions and different time of the ecg change, the information obtained from a 2.16 Km long, more than 10 ten thousand cardiac and more than 10 ten thousand cardiac cycle, has now become a diagnosis of arrhythmia, myocardial ischemia, assess pacemaker function and efficacy of new and high technology.
1.2.3 phone ecg monitoring
Phone transmitting ecg monitoring refers to the transfer of the patient's ecg information by telephone to the monitor/receiving centre for computer processing, medical personnel according to patients' symptoms and transmit electrocardiogram (ecg) after analyzing its judgment calls for diagnosis, nursing and treatment of guardianship, is easy to use, not restricted by time, space and geography, etc. It is cardiovascular ecg monitoring system in the domain of a breakthrough and progress, and its application to outside emergency care heart disease, heart disease hospital home phone remote diagnosis and treatment, nursing has very important significance.
TTM as clinical ecg monitoring extend outward to the hospital, a new method, the cardiac arrhythmia, myocardial ischemia and myocardial infarction has reliable monitoring effect, with symptoms, accidental, temporary cardiac arrhythmia and transient myocardial ischemia has a unique monitoring role. For severe arrhythmia, myocardial infarction and angina pectoris, it is more accurate electrocardiogram (ECG) diagnosis, emergency treatment and nursing of outside heart disease hospital guidance are of great value. It greatly shortens the patient, the distance between nurses and patients, give patients a sense of security, so as to stabilize the patients nervous psychological state, eliminate the psychological pressure and burden, reduce the inducing factors of heart disease. As in long-term care patients, first aid and nursing instruction at the same time, constantly improve the self-help, self nursing ability.
TTM system in the domestic application in its infancy, hospital emergency care is a new subject, for further study, summarize and improve, in order to better benefit the whole society of patients with heart disease.
But now, there are a lot of ecg monitor has not gained popularity, there are still some problems:
(a) to provide electrical processing and recording of ecg information co., LTD., a doctor is difficult to get a comprehensive electric information, reduce the accuracy of the diagnosis of doctors to disease.
(b) is generally adopted the digital signal processor as the core device of ecg data analysis, and data communication, LCD display, real-time clock, need to be extended special functions such as program memory device, so the structure is complicated,
Volume is larger, power consumption at the same time also is bigger, the price is expensive, general patients.
(c) to form a complete set of monitoring network and ecg data processing center is still not perfect.
1.3 ecg monitoring system for the future development direction and prospects
The traditional ecg monitor based on PC platform is expensive, bulky, not easy to move and are mainly concentrated in large hospitals and unable to real-time monitor the patient's condition, has brought great inconvenience to physicians and patients.
In recent years, with the rapid development of computer network, communication and other related technologies, ecg monitoring technology has been gradually applied to the field of telemedicine, makes the hospital for patients with heart disease remote health care service possible. Ecg monitoring system in the future will have low cost, small volume, high reliability, the advantages of simple operation, will continue to lead to the information, solid record, development direction, such as synchronous collection and is suitable for individuals, small and medium-sized hospitals and community health care unit, to family care and remote medical treatment and other emerging medical way to provide a good help and support.
2 system design scheme comparison
2.1 the overall design requirements of ecg monitoring system
The topic of this subject is based on SCM ecg monitoring system design.
For ecg monitoring signal collecting device to input preamplifier, the signal amplification after 8 times, filtering through the filter circuit, filter out more than frequency of 0.05 Hz and 105 Hz frequency, at the same time prevent 50 Hz frequency interference signal. After filtering of signal through the amplifier circuit to enlarge it to v level, through the adder circuit will increase its waveform to 0 v, is advantageous for the MCU A/D conversion circuit directly into A numeric value. After processing of ecg signals by simple oscilloscope display on the LCD screen, so that users can real-time and convenient to observe heart waves of change and the form.
12864 LCM LCD choosing KS0108 controller, AT89C51 single-chip computer for data processing and display shows waveform.
2.2 the system structural design of ecg monitoring system
For ecg signal acquisition, acquisition of lead with a standard way. Ecg signal is a weak electrical signals, first using preamplifier circuit signal amplification eight times. Due to the exist all kinds of noise source of the human body, in order to offset these interference, can design a compensation circuit. For signal after amplification, make it through the filter circuit filter. Ecg signals exist in the 0.05 Hz frequency, more than 105 Hz frequency signal, and the work of 50 Hz frequency interference signals, need to let the ecg signals through a low-pass filter, high-pass filter and band-stop filter, after filter circuit of signal becomes cleaner. Then for ecg signal amplification to v level, let it through a four-pass amplification circuit. At the same time, to facilitate the single chip microcomputer and ADC0808 signal acquisition and processing, can let the ecg signal through an adder circuit, the waveform to 0 v. Then through display circuit through single chip microcomputer processing signal display on the LCD screen. The whole system structure diagram as shown in figure 2.1.

System structure diagram in figure 2.1
2.3 the feasibility study of ecg monitoring system design
In the learned knowledge, for ecg signal acquisition, can make use of a specific sensor for ecg signal acquisition; For preamplifier circuit, integrated instrumentation amplifier AD620 may be used for the signal of preamplifier; For compensation circuit, can use operational amplifier and feedback resistance compensation circuit; For filter circuit, can take advantage of the active filter circuit is designed by calculation conform to the requirements of the low-pass filter, high-pass filter and band-stop filter; For four-pass amplification circuit, can use the integrated operational amplifier for signal amplification again; For adder circuit, can use the design of the integrated operational amplifier for adder; For ecg signal digital processing and analysis, can use single chip microcomputer and ADC0808 to design hardware circuit; To display circuit, can let the ecg signal is displayed on the LCD. A/D conversion circuit, display circuit and single-chip microcomputer analysis of ecg signal processing to the preparation of the software.
Through the argumentation, the system structure design scheme is feasible, can reach the design request of the ecg monitoring system.
3 hardware circuit design
3.1 ecg signal acquisition circuit design
Clinical up electrical signals collected mainly from the body surface, when test will measure electrode placed on body surface at intervals of two points, the electrode by more strands insulation core into the shielded wire connected to the amplifier in ecg monitor and measure the electrode potential difference is on the body surface ecg signals, tracing curves is the electrocardiogram (ecg). In the determination of ecg signal waveform, the position of the electrodes are placed, and wire connected to the amplifier, referred to as the "lead" heart all.
Tie the electrode in the medial aspect of the wrist or ankle, and through the long shielded wire connected to the heart all the way is called "standard lead". Traditionally the symbol is defined for these electrodes and the color of the connection wire, as shown in table 3.1.
Table 3.1 lead tag
The part of the electrode arm right leg left leg on his right arm
The symbol RA LA LL RL
Wire color red yellow blue black (green)
Standard lead directly to add two body potential to ecg amplifier's input, the waveform is described the change of potential difference at two o 'clock.
Standard of Ⅰ lead: the right arm (RA) amplifier inverting input terminal (-), left arm (LA) amplifier in phase input terminal (+), right leg (RL) as the reference electrode, the reference point in ecg amplifier.
Standard of Ⅱ lead: the right arm (RA) amplifier inverting input terminal (-), the left leg (LL) answer the in-phase amplifier input (+), right leg (RL) as the reference electrode, the reference point in ecg amplifier.
Standard lead Ⅲ: left arm (LA) amplifier inverting input terminal (-), the left leg (LL) answer the in-phase amplifier input (+), right leg (RL) as the reference electrode, the reference point in ecg amplifier. This subject adopts standard Ⅰ guide mode, right leg (RL) of the reference electrode connected compensation circuit [3].

Signal acquisition circuit input schematic diagram in figure 3.1
In this design, with a standard Ⅰ guide mode, namely, as shown in figure 3.1, the IO1 end as the reference electrode to the right leg, IO2 termination left arm, IO3 termination right arm.
3.2 the preamplifier circuit design
The design of the preamplifier circuit adopts integrated instrumentation amplifier AD620. Because of this design to deal with electrical signals are faint, and the demand is higher, the quality of the waveform with high input impedance, high common mode rejection ratio, low noise and low drift. So in this design can choose integrated instrumentation amplifier AD620 to carry out the design of the preamplifier circuit.
3.2.1 AD620 chip
Internal is composed of three common amplifier AD620, its pin diagram as shown in figure 3.2. In use, Rx chip 1, 8 feet, 4, 7 feet plus or minus the same working voltage, input the weak voltage signal of 2, 3, 6 feet for the output pin, 5 feet benchmark for reference.

Figure 3.2 AD620 pin drawing
This can be designed by adjusting the Rx AD620 to adjust the size of the gain value, the gain can be calculated by formula (3.1).
(3.1)
AD620 gain range is 1 ~ 1000. It has low power, high precision, low noise, good temperature stability, amplification bandwidth, noise coefficient is small, higher common mode rejection ratio, easy adjustment, etc. The chip can provide the maximum current of 1.3 mA of current. Applicable to the ECG measurement, medical devices, pressure measurement, signal acquisition, etc.
3.2.2 preampli