ECG Monitoring System Based on TMS320LF2407ADSP

With the development of society and the improvement of people's living standards, people pay more and more attention to health, but with the improvement of living standards, the incidence of cardiovascular diseases continues to rise.

Especially in recent years, with the increasing aging of society, cardiovascular disease has become a major disease threatening human life, and heart disease has become the disease with the highest mortality rate in the world. In view of the increasing number of patients with cardiovascular disease, it is imperative to improve the means of preventing and monitoring the disease. ECG signal detection is the most direct means of detecting heart disease, but the ECG monitors currently used in hospitals are almost all imported, expensive, and high maintenance costs, which increases the economic burden on hospitals and patients; therefore, it is of great significance to design a portable and economical ECG monitoring device. This paper designs an ECG monitoring system based on TI's TMS320LF2407A DSP. This system is small in size, low in cost, and highly practical.

TMS320LF2407A DSP Introduction

An important part of the ECG monitoring system is to process ECG signals, so it is very important to choose a suitable signal processor. The most successful DSP chips at present are the series of products from TI in the United States. Its three main DSP platforms, TMS320C2000, TMS320C5000 and TMS320C6000, have become the most influential DSP chips in the world today.

This system uses TMS320LF2407A as the signal processor and core controller. TMS320LF2407A is a new high-performance 16-bit fixed-point digital signal processor launched by TI and a new member of the TMS320C2000 series. It is specially designed for digital control, integrating the high-speed signal processing capability of DSP and the optimized peripheral circuit suitable for control. It is a true single-chip controller and has been widely used in digital control systems.

TMS320LF2407A DSP has the following features:

(1) The use of high-performance static CMOS technology reduces the power supply voltage to 3.3V, reducing the power consumption of the controller; the execution speed of 40MIPS shortens the instruction cycle to 25ns, thereby improving the real-time control capability of the controller.

(2) Based on the TMS320C2xx DSP CPU core, the TMS320LF2407A DSP code is guaranteed to be compatible with the TMS320 series DSP code.

(3) The chip has up to 32KB of FLASH program memory, up to 1.5KB of data/program RAM, 544 words of dual-port RAM (DARAM) and 2KB of single-port RAM (SARAM).

(4) Two event manager modules EVA and EVB, each including two 16-bit general-purpose timers and eight 16-bit pulse width modulation (PWM) channels.

(5) Expandable external memory with a total of 192K words of space: 64K words of program memory space, 4K words of data memory space and 64K words of I/O addressing space.

(6) Watchdog timer module (WDT).

(7) The minimum conversion time of the 10-bit A/D converter is 500ns. Two event managers can be selected to trigger two 8-channel input A/D converters or one 16-channel input A/D converter.

(8) Controller Area Network (CAN) 2.0B module.

(9)Serial communication interface (SCI) module.

(10) 16-bit serial peripheral (SPI) interface module.

(11) Phase-locked loop based clock generator.

(12) Up to 40 general-purpose input/output pins (GPIO) that can be individually programmed or multiplexed.

(13) Five external interrupts (two electrode drive protections, reset, and two maskable interrupts).

(14) Power management includes three low-power modes, which can independently switch peripheral devices into low-power mode.

(15) It has encryption function and the key length is 64 bits.

System hardware structure

The whole system can be divided into the ECG signal acquisition part and the signal processing part. The signal processing part uses TMS320LF2407A as the processor, and expands the external memory, LCD display, buttons and serial communication interface.

Power supply is the primary condition for the system to work. This system uses two voltages, 5V and 3.3V. The system input power voltage is 5V DC, so conversion is required. This system uses AMS1117-3.3 for 5V~3.3V voltage conversion, and the light-emitting diode D3 is the power indicator.

The electrocardiogram (ECG) acquisition circuit collects ECG signals through sensors and then sends the collected analog signals to the 10-bit A/D input terminal integrated in the TMS320LF2407A for A/D conversion. Two event managers are used to trigger a 16-channel input A/D converter to improve the conversion accuracy and accurately collect weak ECG signals.

TMS320LF2407A integrates 1.5K RAM and 32K FLASH. The capacity of 32K FLASH is basically enough, but the internal RAM storage space is too small. In order to save a large amount of sampled data, intermediate results of calculations and improve the operating speed of the system, the system adds external data memory (RAM) and external program memory (RAM), which are selected by PS and DS signals of TMS320LF2407A respectively. The RAM memory used in this system is two IS61LV6416-10T, which has a storage capacity of 64K 16 bits. The data access time is 10ns, which can meet the needs of high-speed operation. The operating voltage is 3.3V, which is consistent with the DSP operating voltage, and no level conversion circuit is required.

The LCD module is used to display the ECG, so that the user can observe the ECG intuitively without a PC. The ECG can also be displayed by the PC by connecting it to the serial port. When not used to display the ECG, the LCD can display the system status and other information. This LCD module contains a SED1335 controller with a resolution of 128 128. The module is characterized by low power consumption and strong anti-interference ability. The module integrates a LCD display controller, driver, RAM, ROM and LCD display. When using it, you only need to send the corresponding commands and data to the module to display the required information. The interface with the DSP is simple and convenient and flexible to use. The TMS320LF2407A is powered by 3.3V, and the LCD module is powered by 5V, so they must be connected through a level conversion circuit. This system uses SN74LV16345A to achieve level matching.

TMS320LF2407A integrates a full-duplex asynchronous serial port, which can realize the communication between the ECG module and the PC or other devices. However, RS232 level and TTL level are not compatible, so we use a level conversion chip MAX232, which uses a +5V single power supply, has a simple circuit and is easy to use.

In order to facilitate the setting, the system also adds a button module, through which users can control some functions of the system, such as start and stop.

Software Design

Understanding and analyzing the characteristics of ECG is the basis for studying ECG signal detection. Designing detection algorithms for corresponding frequency bands based on the characteristics of ECG in different frequency bands is an important task in software design.

The electrocardiogram is composed of a series of wave groups, each of which represents each cardiac cycle. A wave group includes P wave, QRS complex, T wave and U wave. Studies have shown that the main bands of the electrocardiogram are QRS wave, R wave and P wave. Heart rate variability (HVR) analysis has received widespread attention in clinical research and is the main method for analyzing electrocardiogram abnormalities. The object of heart rate variability analysis is the RR interval of the electrocardiogram waveform. When the system samples the data, it locates the R wave of the waveform, finds the position of the R wave, calculates the RR interval between adjacent R waves, and then stores it. The task of the system software is to filter the collected electrocardiogram signal, then perform heart rate variability analysis, calculate the RR interval, and finally display the final electrocardiogram on the LCD screen.

After all programs are debugged, use the emulator's FLASH programming program to download the target code to the FLASH of TMS320LF2407A through the JTAG port to achieve independent operation of the entire system.

Conclusion

This paper designs an ECG monitoring system with TMS320LF2407A DSP as the signal processor. The system integrates the acquisition, analysis and display of ECG signals. The system is small in size, low in cost, easy to carry and highly practical.