Design and implementation of wearable ECG monitoring system
Abstract: The comfort and durability of wearable medical devices are receiving more and more attention. In this paper, the conductive fabric is used as the ECG electrode of the ECG monitoring terminal, and the wearable ECG acquisition system is designed according to the characteristics of the fabric electrode. The system mainly consists of two parts: ECG acquisition analog front end and single chip system. The ECG acquisition analog front end mainly performs the amplification and filtering of the weak ECG signal collected by the fabric ECG electrode to obtain a stable ECG waveform with high SNR. The MSP430F149 model chip of TI Company is used as the microprocessor in the single chip microcomputer system. The microprocessor-controlled analog signal is converted to a digital signal and written into the Flash. Finally, you can communicate with the computer serial port and upload the ECG data inside the Flash. The Flash chip uses the Winbond W25Q256 chip with 256 Mbits of memory and can continuously store the patient's ECG signal for 24 hours at a sampling frequency of 150 Hz.
0 Preface
Cardiovascular disease is the most threatening to human life in modern industrial societies. At present, there are more than 270 million people with cardiovascular and cerebrovascular diseases in China, and nearly 3 million people die of cardiovascular and cerebrovascular diseases every year. And cardiovascular disease has a great sudden onset, losing valuable early diagnosis and treatment time, leading to serious consequences, so the best way is to prevent it. Daily cardiac monitoring is an important means to ensure the safety of patients' lives. Pre-discovering abnormal signs through daily monitoring can win time for timely treatment.
Daily monitoring of the human heart condition by ECG signals is an effective way of cardiac monitoring. The long-term use of AgCl electrodes used in traditional ECG monitoring can cause skin irritation and other uncomfortable reactions, and is not suitable for use in daily life. In recent years, many scholars and research institutions have studied the wearable ECG acquisition technology in order to be able to collect the wearer's ECG data in real time under daily activities. Fabric electrodes have been used in wearable human health monitoring systems as early as a decade ago. The fabric electrode is different from the traditional conductor electrode. It directly contacts the skin when measuring the ECG signal. It does not require the use of electrolytic gel or adhesive. It is very suitable for long-term ECG monitoring and can be extended to physiological monitoring. Telemedicine , electronic assistance and sports medicine. Cardiac monitoring systems have been designed in the form of bandages or tights.
Since there is no use of adhesive, the impedance of the fabric electrode and the skin contact position is greatly increased, and it is easily interfered by noise, which affects the quality of the ECG signal, and the relative motion of the electrode and the skin caused by human motion is also Causes changes in contact impedance, which affects signal stability. In this paper, a wearable ECG acquisition system is designed according to the characteristics of fabric electrodes, which can collect stable high signal-to-noise ratio ECG signals under daily activities.
1 system structure
According to the characteristics of the fabric electrode, the ECG detection circuit is designed, and the long-term acquisition and storage transmission function of the ECG signal is completed based on the MSP430 MCU. The system mainly includes two circuit modules, namely an ECG analog front-end conditioning circuit and a MSP430 system peripheral circuit. The structure of the system, see Figure 1:
The wearable ECG monitoring system can realize the following functions: 1 ECG signal acquisition and storage function. According to the spectral characteristics of the ECG signal, the sampling frequency of the ECG signal is 150 Hz, the AD sampling resolution is 12 bits, the terminal can save the patient's 24 h ECG data, and the Flash capacity can be expanded according to the requirements to achieve longer acquisition and storage; The ECG signal upload function is used to realize the off-line analysis of the patient's heart condition; 3 system low power consumption.
1.1 ECG analog front end design
The ECG analog front end realizes the function of extracting, amplifying and filtering the ECG signal. The block diagram of the ECG analog front end, see Figure 2:
Figure 2 Analog Front End Circuit Structure
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