According to the objectives of the "National Health Information Development Plan Outline" of the Ministry of Health, the hospital will be basically digitized and informatized in 2010. Therefore, the future medical device market has huge market space for new medical equipment, especially the ECG signal processing system with digital and information features has broad application prospects and practical value.
After the ECG signal is extracted into the system through the electrodes, it is amplified and filtered by an amplifier circuit with a high common-mode rejection ratio, and quantized by a high-precision serial A / D conversion device, which improves the accuracy of the signal. This system uses the 32-bit high-speed ARM processor as the hardware platform and the real-time operating system as the software platform to schedule and allocate the resources of the hardware system to achieve the effect of real-time processing of ECG signals, and to achieve the ECG Signal real-time display, real-time storage and other functions.
Overall system design
The main function of the system shown in the figure is to process and transmit ECG signals in real time, as shown in Figure 1.
Figure 1 System functional block diagram
The ECG signal is extracted through the electrode and enters the analog processing module. After the analog processing part is amplified and filtered, the signal strength and signal-to-noise ratio are improved. The signal is converted into a digital signal after quantization, and enters the digital processing module. In the digital processing module with the ARM processor as the core, the software module of the PC includes the reception of the USB channel data and the processing of the ECG signal. The ECG signal further improves the signal-to-noise ratio and is displayed on the screen, so that it can better assist the doctor's treatment of the patient and can ensure the normal progress of medical treatment.
1 S3C44B0X processor
The S3C44B0X microprocessor is a high-performance and cost-effective microcontroller solution specially provided by Samsung for portable devices. It uses a 32-bit low-power RISC core ARM7TDMI and is manufactured using a 0.25μm CMOS process to support the new bus structure SAMBAII.
The working principle of the system with S3C44B0X as the core: First, the patient's mixed ECG signal is obtained through the medical Ag-AgCl electrode, the signal conditioning circuit amplifies and filters the bioelectric signal, and then A / D conversion, and then through the 32-bit microprocessor Algorithmic separation of the collected data, real-time display of the patient's disease waveform and storage of data; embedded real-time operating system (RTOS)? C / OS-â…¡ coordinates the work of various functional modules, so that the system has high real-time and reliability .
The main functions integrated on the chip are: add 8KB Cache on the basis of ARM7TDMl; external expansion memory controller; LCD controller supports up to 256-color DSTN, and has 1 LCD dedicated DMA channel; 2 general DMA channels, 2 DMA channel with external request pins; 2 DARTs with handshake protocol: 1 SIO; 1 I2C bus controller; 5 PWM timers and 1 internal timer; watchdog timer; 71 general-purpose Programmable I / O port, 8 external interrupt sources; power control modes include normal, low, sleep and stop; 8-channel 10-bit ADC; RTC with calendar function; PLL clock generator.
2 Real-time operating system μC / OS-II
μC / OS-II is an embedded real-time operating system kernel with open source code. From now on, from 8-bit to 64-bit, this operating system has been run on more than 40 microprocessors with different architectures. ΜC / OS-II has been used in many fields in the world. Using this kernel can make application design and expansion easy, and new functions can be added without major changes. By dividing the application into several independent tasks, RTOS greatly simplifies the application design process.
Hardware system design
1 UART asynchronous serial interface design
After the ECG data is scheduled by the real-time operating system, it is transferred to the PC through the USB channel. However, due to the complexity of the USB interface, an asynchronous serial interface is required when debugging the USB device. Moreover, when the USB driver cannot be used or installed on some old PCs, the asynchronous serial interface can be used as a backup low-speed transmission method, which also increases the scalability of the system.
Figure 2 is the connection diagram of the serial interface circuit of the S3C44B0X with RS232 level conversion in the ECG signal processing system. In the figure, the RS232 level conversion chip is MAX3232, and its RxD0, TxD0 and RxD1, TxD1 are connected to pins 99, 100 and 103, 104 of S3C44B0X, respectively.
Figure 2 Serial connection diagram
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