And other ECG machine highlight the difference is that the system uses the new low power 16-bit microcontroller--MSP430 F135 as overall system control core, and equipped with corresponding 16-bit low power consumption memory AT29LV1024 and LCD module LMS0192A, thus simplifying the system hardware circuit, but also significantly reduces system cost, thus this household ECG has a very broad application prospects.
First, an overview
Cardiovascular disease is one of the more common diseases, with the acceleration of the pace of life, living standards and health awareness that people need to be at the heart of health care and more critical to timely diagnosis and treatment; at the same time, if the long-term stay in hospital for care and treatment inside, so expensive and also gave the hospital brought no small outpatient pressure.
ECG is an important instrument for heart disease diagnosis, there are several on the market today, but these electrocardiograph ECG machine is not suitable for use in the family. To do this, an application can be in the family, the operation simple, inexpensive and low-power electric diagram of machine design emerged.Total is well known that with the advance of science and technology, the development of human society, the development of the global medical devices is changing.
21st century healthcare industry main rendering the following two features: first, the future health care world, the main representative products are Nano-mechanical components, along with wearable chemical sensors, in-home care to medical equipment, etc. Secondly, information and medical technology closely together. Household ECG machine design is adapting to the two main trends. In addition, from the outbreak of the SARS virus, can be expected, it will promote the application of home health care medical equipment development. Therefore, household ECG machine at home and abroad are a new type of product, has a great market potential.Second, function and basic principles
(A) overall design
In order to reach the heart of the "health care" and "family clinic", the household ECG machine has the following basic functions:
Using liquid crystal display real-time ECG waveform display and menu;
Use of external memory will store the information saved in the ECG for future reference as diagnosis and treatment;
Use the printer will print archive; ECG
You can organize the records saved user information;
Multiple modes of operation, automatic, manual operation can be selected;
You can easily collect from the human body to the ECG signal is transmitted to the relevant medical institutions.
Taking into account the needs of the user's actual use, household ECG machine also must meet the following characteristics:Anti-interference;
Small size, light weight, easy to carry;
Simple operation;
Low power consumption;
In order to widely promote lower production costs, and must have good performance price ratio.
The household ECG is battery-powered, battery power supply needs to be fixed is a fundamental contradiction: low power requirements system with relatively low clock frequency and at the same time request system on some basic operation to quickly react and boot the system, this requires at least a two level different frequencies and, if necessary, you can switch between two frequencies. Precisely because the MSP430 F135 has a rich and flexible clock module, the system selects it as the control core, at the same time also the use of companion low power external storage AT29LV1024 and LCD module LMS0192A.Texas Instruments ' MSP430 provided for high integration and high-precision single-chip system, is the industry's lowest power consumption in a flash 16-bits RISC microcontrollers.
MSP430 F135 with powerful processing capabilities and a rich peripheral module, you can easily achieve the ECG signal acquisition, processing, storage, printing and transmission. In addition, as a system of control core, you can greatly simplify the entire hardware circuit and improve the system of price and performance.ECG Electrode or lead wire from the human body collection, amplification, filtering processed into microcontroller made A/D conversion, the LCD display.
If you need to save it press the save key ECG data will be stored in the external memory, and the need for playback, print, transfer, you can directly from the external storage for use to realize various functions. You can directly use the network or the telephone to the household ECG monitoring data transfer to the medical institution, after the diagnosis, treatment by medical institutions, and thus facilitate feedback and efficiently enables the family clinic "and" health surveillance ", saves the user the relative expenditure reduced hospital outpatient pressure. This system incorporates a shown in Figure 1 the structure of the circuit.(Ii) detection of ECG and acquisition
Household ECG the required detection of amplitude in the ECG 0.05 ~ 4 mV, frequency in 0.05 ~ 72Hz.
While testing the main interference signals with electrode plate and polarization voltage, power frequency interference, apparatus 50Hz internal noise and electromagnetic fields around the electric field instrument of interference, etc. ECG 50Hz frequency interference can use adaptive template method to eliminate, ECG machine simulation parts can be used as shown in Figure 2 structure of the hardware. ECG lead by the electrode or line acquisition, the first to make amplification voltage. Voltage amplifier usually consists of two levels, of which the first-level using negative feedback differential amplification circuit. The system uses TI company based on a dual operational amplifier circuit of micropower instrumentation amplifier INA321 chip as the first ECGPreamplifier, magnification 10 x. Due to the interference signal 72Hz more than strong 0.05Hz following relatively weak signal interference, so the filter circuit, taking first low pass filtering out 72Hz following signal, and then add high-pass, so that you can filter out polarization voltage signal receive ECG. As in the previous filter circuit using RC high-pass filter circuit, the circuit has a high output impedance, so after amplification using phase amplifier, the magnification is 20 times.ECG maximum amplitude as 4mV, after 200 x magnification, for 0.8V A/DC input range is 0 ~ 2.5V, design time for intermediate values for reference, so 1.25V enlarged ECG overlays reference voltage 1.25V after size (1.25 ± 0.8) V, just drop in A/DC analog input signal range.
At the same time, the frequency of the ECG in 0.05 ~ 72Hz, in order to ensure that the sampling theorem of requirements and ensure the slew rate you can choose the sampling rate fs = 200Hz. MSP430 F135 comes with high-speed 12-bit successive approximation type ADC12, ADC12 have internal reference voltage, sample and hold, and auto-scan function, eight-channel 4-channel, up to 200KHz sample rate, and a variety of sampling mode, the ability to meet requirements.Figure 2 simulation circuit diagrams
(3) single-chip system-MSP430 F135
Based on the features, prices, power consumption and household ECG machine design of the actual need for several reasons, the system selects with 12-bit ADC's ultra low-power microprocessor MSP430 F135 as system control core, it is a TI company at the end of 2000 a new ultra-low power Flash-16 bit RISC instruction set chip.
It has a wealth of on-chip peripherals, is a cost-effective high-chip. Use it for ECG signal acquisition and processing, not only greatly simplifies system hardware circuit, also greatly improved the system of price and performance. MSP430 F135 structural principle as shown in Figure 3.By structure schematic diagram, MSP430 F135 contains Flash and RAM 16KB 512B above with the following peripherals: basic clock system (on-chip DCO and two crystal oscillators), watch dog timer/general purpose timers, with 3 capture/compare register 3 and PWM output 16-bit timer Timer_A, with 3 capture/compare registers and PWM output 16-bit timer Timer_B3, i/o port 1 to 6 (each with 8 I/O, which ports 1 and 2 have interrupt function), comparator _A, 12-bit A/D converter ADC12, universal serial synchronous/asynchronous interface USART0.
MSP430 F135 contains a with eight external channel 12-bit high-performance A/D converter, an automatic scan functions with a capacity of 16 characters programmable buffer, on-chip reference voltage, temperature sensors and the battery voltage detection circuit, when A/D converter speeds up 200KHz.
Use of chip built-in auto-scan feature, A/D converter can do not need the assistance of the central processor and independent work, and will be converted to buffer the data automatically. In this way, the central processor workload is reduced significantly. In other words, you can let the processor to execute other digital signal operation or go into power saving mode. In addition, the built-in reference voltage and temperature sensors can reduce the number of external components and reduce the overall cost of the system. ECG after 200 x magnification after the port 6 into the a/d converter with analog-digital conversion, the conversion results are automatically stored in the corresponding channel register, and then sent to the external ECG storage.Due to the built-in power consumption extremely low fast flash memory, MSP430 F135 in standby mode consumes less battery is not used for natural losses.
In addition, it can be within the 6ms from standby mode immediately go back to full working mode, because during the startup process devices won't waste any time, thereby extending battery life. In normal working state, if the working voltage of 2.2V, devices each MIP consumes A current only 250 μ.MSP430 F135 ROM with on-chip Flash, to a user for debugging a great convenience.
Most of the current development environment using IAR WORKBENCH software company's WINDOWS, and matching a TI company providing development kit MSP-FET430P140, can realize functions for program downloads, updates, run, debug. By PC environment JTAG control FLASH programming, a simulation by on-chip logic control full speed debug breakpoints can be set to 3. Users in your target Board leads to JTAG leads to debug device may implement the program for download and debugging.MSP430F135 basic clock system including a chip DCO and two crystal oscillator, can produce three system applicable clock signal: ACLK, MCLK and SMCLK.
Of these, the main system clock MCLK for CPU and system, auxiliary clock ACLK and subsystem clock SMCLK for peripheral modules. You can pass on different module operation mode and CPU status of intelligent management, makes the MSP430 F135 works can adapt to a variety of ultra low voltage and ultra low-power requirements, even in the interrupt processing period, too, a disruptive events can make system from various low-power modes wake and RETI instruction returns to interrupt a previous working state. The following is the MSP430F135 chip supports six working mode:1) activities (AM): CPU and different combinations of peripheral module is activated, the active; 2) low-power mode 0 (LPM0): CPU stopped working, peripheral module to work effectively, ACLK and SMCLK MCLK loop control; 3) low-power mode 1 (LPM1): CPU stopped working, peripheral module to work effectively, ACLK and SMCLK MCLK loop control is not valid; 4) low-power mode 2 (LPM2): CPU stopped working, peripheral module to work effectively, SMCLK ACLK MCLK loop control and is not valid; 5) low-power mode 3 (LPM3): CPU stopped working, peripheral module to work effectively, SMCLK ACLK MCLK loop control and is not valid and digitally controlled oscillator DCO DC generator is turned off; 6) low-power mode 4 (LPM4): CPU stopped working, peripheral module continues to work (if you supply an external clock), ACLK signal blocked, crystal oscillator stop working, SMCLK and MCLK loop control invalid and digitally controlled oscillator DCO DC generator is turned off.
From the MSP430 F135 of ultra-low power performance of the main and its clock generation and control.
The design of the ultra low-power CPU's in most of the time is in hibernation. MSP430 F135 5 low-power mode, the main CPU completed the appropriate settings, or task after the let CPU into appropriate low-power mode. CPU required to complete the bulk of the work is done in the interrupt service program, the corresponding interrupt wake up CPU interrupt service is completed, execution is complete, and then enter low power mode. Thus by software on the internal clock on the system settings to control the chip so that it is in a different way of working. The entire clock systems and provide a wide range of hardware and software combinations to achieve the lowest power consumption and optimal system performance.(4) external ECG data storage--1 Mbit 3V-powered flash programmable can be electrically erasable 16 bit memory AT29LV1024 AT29LV1024 is a 3V system powered flash programmable can be electrically erasable 16-bit memory (PEROM) having 1M bit storage space, 1M bit storage space into 512 partitions, each partition is 128 characters.
The chip with ATMEL company advanced non-volatile COMS process manufacturing, use temperature range memory access time 150ns, power consumption of only 54mW. When AT29LV1024 is in hibernation, the CMOS to maintain current does not exceed A 50 μ. Each partition AT29LV1024 erasable 10,000.With power-down protection AT29LV1024, easy online programming skills not required high input voltage, instruction in 3V voltage to control AT29LV1024.
Read data from AT29LV1024 and action, similar to the EPROM and programming skills to each partition as a unit, 128 characters of data into AT29LV1024 while completing programming. In a longer programming cycle, all storage units of addressing and 128 characters of data through the internal latch to release the address and data bus, this may provide for other address and data bus. Programming cycle start AT29LV1024 automatically erase the contents of the partition, and then on the latch data under the function of the timer to be programmed. The end of the programming cycle is through query I/O7 or I/effective at achieving O15, once the programming period ends, you can start a new reading or programming operations.AT29LV1024 works as shown in Figure 4.
AT29LV1024 is a new type of memory that has the following characteristics:
(1) 3V ~ 3.6V supply area;
(2) a single 3V read and write operations;
(3) hardware and software data protection;
(4) fast read time: 150ns;
(5) low-power consumption: 15mA effective current 50 μ A CMOS maintain current;
(6) partitioning programs: erasable, programmable, one-way revolving 512 partitions (128 words/partition), the internal address and data latch 128 characters;
(7) quick partition programming cycle: 20ms;
(8) the internal procedure and Timer control;
(9) the query is ended;
(10) typical erasure, programming can be more than 10 000;
(11) CMOS and TTL compatible input and output;
(12) of the commercial and industrial temperature optional scope.
In a domestic single channel ECG machine, use outside microcontroller chip AT29LV1024 as expanded data storage, storage of ECG data, these data can be stored online in real time using or want to read from memory.
The power-down protection AT29LV1024 feature unexpected power-off, or turn off the power to save the data, this will not only ensure that the data *, and you can save power. Because AT29LV1024 for program memory also may make the data memory, thus here holds from human ECG data collected, these data through a single chip A/D conversion for ECG of digital, the digital signal is first stored in a single-chip microcomputer internal RAM, when the internal RAM 128 characters after save full data, stored in the external data memory AT29LV1024, future requires the use of these data, it can be read from AT29LV1024. AT29LV1024You can save or modify a few paragraphs ECG waveform in different periods, for example: a user's daily cases for future reference. When you need to update these data can be electrically erasable update the stored data, to store the new ECG data.Thanks again from AT29LV1024 programming ability is to each partition as a unit, 128 characters of data into AT29LV1024 while completing programming, its each operation is a 128-character units, each time the storage, update is 128 characters, and every time before you send the Word data 128 require initial operation, procedures are as follows:
AT29LV1024 application of the system so that users can quickly realize the desired functionality, and electrically erasable for program and data storage and update provides convenient, especially its power-down protection features to unexpected power-off, or turn off the power to save data, ensure that the storage of * sexual and reduced power consumption, is previously used RAM does not have functionality for ECG data storage is very convenient, for example, from the human body by sampling a/d values can be stored in AT29LV1024 for playback, print, transfer call.
(V) liquid crystal display system--LMS0912A LCD module
LMS0192A LCD module is a small LCD system, its apparent size 79 x 42mm, 44 pin.
160 × 64 dot matrix displays, point size is 0.30 × 0.34 (mm), dot pitch 0.34 × 0.38 (mm). Internal large-scale integration with drive and controller, it directly affected by the microcontroller, receive an 8-bit serial or parallel display data at the same time, you can display data and to store the data in the chip data storage (DDRAM). DDRAM in data display unit with LCD dot matrix units there is a one-to-one relationship and LMS0192A LCD module data read and write operations from external clock control, thus LMS0192A display have a very high flexibility. LMS0192A LCD module with LCD drive circuit must be power so the available a minimum of components and minimal power consumption for the module's functionality.In micro household electrocardiograph with LMS-0192A LCD module as menu and display of ECG waveform.
It MSP430 as LCD microprocessors, through SCM ECG data acquisition and processing, output to the LCD display.1, interfaces: MSP430 and LMS-0192A interface as shown in Figure 5.
3. display of Chinese characters menu: the menu is mainly composed by Chinese characters, Chinese character fonts will each character is converted to a 16 x 16 dot matrix total of 32 hexadecimal data sent LCD display.
Each character of the data correspond to a table, a program can display kanji lookup.4, ECG waveform display: ECG waveform is a series of curves on the LCD to display these curves need corresponding dot matrix display, with a mind power curve, starting to show the data points in the Start column only displays, from the second data point that you want in the next column shows a data point to the data points on a line segment.
Specific methods are available through the hex data divided by the total number of pages more than 8, and, for this data point is on the page, the resulting balance for this data point the number of rows on the same page. Note that each data point in the appropriate column because the column addresses each sent one data automatically plus 1, and each time the read data from DDRAM must guarantee the position of the column correctly, otherwise the curve of confusion. So use the LCD module LMS-0192A ECG waveform to print or read directly from the LCD, provide a basis for diagnosis.5. LCD initialization procedures are as follows (module uses must be sent to the PIN/RES/RES signal, signal,/RES module can be automatically set default values.
):(6) the transmission of ECG by phone--pulse width modulation method
In the household, ECG machine equipped with pulse width modulation telephone transmission that features.
Here uses pulse width modulation of the basic principle, and according to actual needs presented an improved pulse width modulation method for pulse width modulation and demodulation of hardware and software for simple, low distortion after demodulation, can achieve rapid telephone transmissions. Its main principle as shown in Figure 6. Users at home or any place where a telephone can be stored in the household electrocardiograph ECG driven speaker via voice coupled through the telephone network is sent to the hospital. The hospital's receiving system after amplification, filtering, the use of comparators have pulse waveform, the waveform after entering SCM through program calculates each pulse represents sampling values, single-chip will be sampled values using serial communication sent to the computer, the computer program by the VC ++ reproduces ECG waveform processed.1. send part of the ECG MSP430 F135 12-bit A/D sampling values stored in the external data memory, when the need for phone time from an external RAM, and low 10 bits are used to control timer with sampled values generated width of pulse, the pulse will be considered after sampling modulation of pulse signal (Figure 7, which τ 1 is the first sampled values correspond to the pulse width, T1 is the first sample values of the pulse cycle, similarly τ 2 is the second sampling values correspond to the pulse width, T2 for the second sample value of pulse cycle), this pulse-driven speakers through the telephone network is sent to the hospital.
Telephone transmission signals in the frequency range of 300-1300Hz, 300Hz corresponds to the value of the sampling time τ be 1.667ms = 1667 μ s, timing values corresponding to the timer τ ' = 0682H, timer TH0TL0 = F97DH (timer 0 plus count), The corresponding 1300Hz timer timer value τ ' = 0180H, timer TH0TL0 = FE7FH (timer 0 + count). Thus all the timing values sampled values 0180H <τ'<0682H,由于采样值可能为零,所以在采样值的基础上加上0200H（> 0I80H) base value, this value using 10-bit sampling, up to 03FFH, minimum 0000H, plus the base value of 0200h ≤ τ τ ' ≤ 05FFH in ' allow scope and therefore can accurately transmit without distortion.2. the receiving part
Mini home ECG machine equipped with a receiver system, Speaker BEEP after receiving a signal from dual operational amplifier TL062 constitute the lowpass filter cutoff frequency, f = 1/2 to Π C 1 R 2 = 1300Hz and magnification 3.3 × 106/100 × 103 = 33, the second level constitute TL062 comparators, the input signal to the comparator as pulse width change, every change square wave pulse width represents one receive ECG sampled values, this pulse wave into SCM recovery by calculation after the ECG sampled values.
(VII) menu interface and keyboard interface
In the household electrocardiograph, provides four key for user actions, corresponding to the relevant menu on an LCD monitor.
Menu includes: welcome menu, main menu, secondary menus, and so on three levels, are provided by the LCD display. Each level menu provides to the user a simple tip user-friendly, thus users in menu prompt press a key (A, B, C, D four key) to complete the operation. For example: the main menu is displayed as shown in Figure 9:This machine uses the independent press, the direct use of I/O port-line form a single key press circuit.
Each key has a separate I/O port line, and its status does not affect other I/O port line of work status. Due to the MSP430 F135 ports 1, 2, are interrupted function so you can use the interrupt mode stand-alone press circuit, circuit connection as shown in Figure 10:Due to the use of the process, every keystroke and LCD menu, so as to achieve a single press on to different functions, so the simple free-standing press circuit also does not meet the needs of design, where you must use the soft keys polling technology.
Soft key technology is used to poll the menus and key combinations with the user interface of the new technology. This technology allows the user to a single function key on the number of options. That is, each key can and a menu of commands or parameters menu, the user can press the appropriate key (such as the cursor keys) to select the required command, that is to adopt the key of the nested method to keep the same keys for different functions.III. Summary
ECG is an important instrument for heart disease diagnosis, there are several on the market today, but these electrocardiograph ECG machine is not suitable for use in the family.
Mini home ECG machine is designed for the majority of users. Its volume is small, easy to carry, easy to use on the road. Simple, functional, inexpensive, low power consumption, good price, applicable to the general application of the family, which will in time, anywhere for cardiac monitoring and health benefits.The mini home single channel ECG's outstanding feature is the low power consumption, good performance.
And other ECG machine highlight the difference is that the system uses the new low power 16-bit microcontroller--MSP430 F135 as the core of the entire system of control. As a result of the powerful MSP430 microcontroller, the system design of hardware circuit and there is a large difference in the past. MSP430 F135 rich peripheral module, so it was relatively easy to achieve an ECG for acquisition, processing, storage, printing and sending, so that the entire hardware circuit is greatly simplified.Reference documents
1.Teaxs Instrument, Inc., MSP430 F135 User's Manual, 2001 2.Teaxs Instrument, Inc., MSP430 F13X/14X Data's Manual, 2001 3.Teaxs Instrument, Inc., MSP430 WINODWS WORKBENCH interface Guide, 2001 4.AT29LV1024A, Atmel Corporation, 2001 5. Li-fen, Li, telephone transmission of ECG by Digital pulse-width modulation method, Journal of electronic measurement and instrumentation 2002 supplement, 1457-1460 6.Topway, Inc., LMS0192A LCD module using the guidelines, 2002 7. Choi Weizhen Zhang Jianxin, authoring, biomedical electronics, Peking University Press 1997 8. Wang Bao Hua editor-in-Chief, biomedical electronics, higher education press, 1998, 9. Sun, Xu Han-Fang aiqing, principle and application of single-chip, Beihang University Press, 1988.
10. Handbook of biomedical engineering (United States) J. haukeland (Kline, Jacob) authoring Xu Zhen-Yiu, translation, translation and publication of Tianjin science and technology, 1993
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