IMTC 2005 – Instrumentation and Measurement
Technology Conference
Ottawa, Canada 17-19 May 2005
Design and Implementation of an Embedded Remote ECG Measurement System Ying-Wen Bai, Chien-Yung Cheng, Chou-Lin Lu and Yung-Song Huang
Department of Electronic Engineering, Fu Jen Catholic University
Taipei, Taiwan, 242, R.O.C.
Email: bai@https://www.doczj.com/doc/aa6828389.html,.tw
– Since an embedded circuit board is lower in cost, smaller in size, and lower in power consumption than a PC. In this paper, we use an integrated embedded circuit board instead of using a PC and interface circuit board with our system, which can provide the ECG measurement of a patient who is outside of a hospital. The collected medical information through computer networks will be stored in the medical information databases for accessing by the medical doctors, nurse, and other related health professionals. Our design integrates several modules such as, an embedded circuit board, a database, a Web server, wireless or Internet transmission, and remote user devices. Overall, our system can transmit the heart beat-rate, body temperature and electrocardiogram to the medical information database from a remote site.
Keywords: Medical Measurement System, ECG, Embedded Circuit Board, Web Server.
I.INTRODUCTION
Tradi ionally, he medical measuremen sys em can be expensive and a medical measurement system can be difficult t o access for a needed pat ient. Moreover such a syst em is neither compatible with the PC and communication standards nor is it easily upgraded. In addit ion, a special pat ient may need a medical measurement syst em t o monit or one’s body condit ion even if t hat individual is locat ed in t he hospit al. Based on t hese requirement s and available t echnology, our design provides a convenient operational procedure ut ilizing an embedded circui board and Web server o provide a remote electrocardiograph measurement.
Typically, an elect rocardiogram is generat ed by a nerve impulse st imulus t o a heart, whereby t he current is diffused around the surface of the body surface. The tiny current at the body surface will build on the tiny volt age drop, which is a couple of μV t o mV wit h an impulse variat ion. This very small amplitude of electrocardiograph, needs to be amplified a couple of housand imes for recording and displaying. Simultaneously, the amplified signal is then input ted int o an analog to digital conversion and through the digital interface inpu ed in o an embedded circui t board. The embedded circui t board uses clien t-server ne t work programming t o transmitting this digital medical signal to the remote database by wireless or wire networks.
Based on t he current soft ware and hardware t echnology, our design provides a convenient operat ional procedure t o conduc t a remo t e elec t rocardiograph measuremen t from outside of a hospital. All of the basic modules can be easily designed and implemented and t hey can be compatible with he current ly used syst ems. In 2003, people used a GSM module o ransmi his digi al medical da a [1], bu he Internet transmission has proved faster t han a GSM module. In our design, we used an embedded circuit board net work module t o t ransmit t ing t his digit al medical dat a. Moreover, due to the improvement of the current software and hardware technology of both computer systems and networks, a remote medical system needs to be redesigned by using more modern technologies, such as: a Web server, the Internet and wireless networks and an embedded circuit board. Hence, Our design includes several modules: an in t erface circui t board, an embedded circuit board, the software on the embedded circuit board for wireless or Internet transmission, and the software for he remo e medical servers. As he embedded circui board sof t ware is a module design using an ANSI C, therefore it is compatible with most current computer devices. Finally, our explana t ion emphasizes t he design of an embedded circui t board and t he remo t e server sof t ware module of an embedded remo t e elec t rocardiogram measurement system.
The rest of this paper is organized as follows. In Section 2, a brief overview of a remote medical measurement system is provided. In Section 3, the hardware modules are discussed. In Section 4, the software modules are designed. In Section 5, t he implemen t a t ion and specifica t ion of t he design are provided. In the last Section, the conclusion is drawn.
II.A BRIEF OVERVIEW OF A REMOTE MEDICAL
MEASUREMENT SYSTEM
An elec rocardiogram is genera ed by a nerve impulse stimulus to a heart, whereby the current is diffused around the surface of the body surface. The current at t he body surface will build on the voltage drop, which is a couple of μV to mV with an impulse variation [2-3]. This very small amplitude of impulse needs t o be amplified t o enable t he recording and displaying. Usually, the electrocardiograph needs a couple of t housand t imes of amplificat ion. The funct ion blocks of t he int erface circuit s of a remot e elect rocardiogram syst em are used to amplify the tiny ECG signal with noise reduction. In our design, t he in t erface circui t is used t o pick up t he elec rocardiograph and amplify his signal by using noise suppression and elec t rici t y isola t ion. The amplified ECG signal is then inputted into an analog to digital converter and through the digital interface inputted into an embedded circuit
Abstract
board. The embedded circuit board uses a LCD to display the signal in t he board at t he client sit e and uses client -server network programming to t ransmit this digital medical signal t o a remot e medical Web server by use of wireless or wire net works. Event ually, t he elect rocardiograph can be seen at the remote site by Web browsers from different users such as medical doct ors and nurses. Sect ion 3 shows t he hardware block diagram and he func ion of he embedded remo e elect rocardiogram syst em. The det ail of t he hardware and soft ware design will be seen at references [2]. Usually, t he Web applica t ions can be designed and implemen t ed by Microsoft Act ive Service Page and t he client s can use t he HTTP prot ocol t o access t he medical informat ion from t he medical Web server, which can be updated by a way of the real time. Fig. 1 shows the system architecture of the remote medical information system. There are a few common t ypes of medical informa ion such as, he hear bea -ra e, body empera ure, and elec rocardiogram can be picked up by using t he measuremen t circui t boards and t he necessary ransmission facili y such as a hub, an E herne and he Internet. This medical information can be transmitted into the Web server and can be accessed by means of a client ’s PC Web browser [4-6].
&Nurses
Electrocardiogram Body Temperature
Heart Beat-rate ???
Fig. 1. System architecture of the embedded remote medical
information system
III. HARDWARE MODULES
Fig. 2 shows t he hardware design of t he medical measurement interface circuit board and the embedded board used to transmit this digital medical signal to a medical web server by net works [5]. The medical signals of pat ient s are t ransmit t ed in digit al form t o a medical informat ion server t hrough an embedded circui t board and In t erne t . The embedded circuit board comes equipped wit h a full Int ernet interface and its operating system (OS), which is a derivative of the Linux 2.0 kernel intended for microcontrollers without Memory Managemen Uni
s (MMUs). However wi h his kernel multitasking can be hard to execute. The uClinux OS has a full TCP/IP st ack which is Int ernet -ready, as well as support for numerous other networking protocols. Some user applicat ions t hat run on t op of uClinux, however, will not require any mult it asking. In addition, in our design, most of t he binaries and source code for t he kernel have been
rewritten to tighten up and slim down the code base. Overall, he uClinux kernel used in an embedded syst em is much smaller t han t he original Linux 2.0 kernel used in an PC, while at t he same time retaining the main advantages of the Linux opera t ing sys t
em: s t abili t y, excellen t ne t work capability, and file system support [7-8]. Fig. 2. The medical measurement interface and embedded circuit
boards
A. Interface Circuit Board
Fig. 3. The function of the interface circuit board
The operation procedure shown in Fig. 3 can be explained as follows:
1. In Fig. 3, t he ECG sensor is used as t he input st age, which requires very high impedance that is often attained by using a CMOS inpu circui in order o bo h ma ch he impedance of the ECG signal source and to pick up a larger amplitude of the ECG signal.
2. Due to the difficulty of the reduction of the noise in the very small amplitude of an electrocardiogram signal, we need to use a differential amplifier to suppress the common-mode noise. In addit ion t o prevent ing any elect rical shock t o t he t est ed body, we use an isolat ed amplifier t hat can not only amplify t he ECG signal but also provide DC power supply isolat ion by means of a magnet ic coupling mechanism. To amplify t he elect rocardiogram signal furt her, we use a main amplifier. However, because he DC offse vol age could saturat e the amplifier, we must adjust t he DC offset voltage of the amplifiers very carefully.
3. Because the medical signal can induce the noise nearby he loca ion of he ECG, we need o use a 60 Hz band rejection to suppress this noise and a low pass filter to reduce the high frequency noise. In addition, to minimize the error of any component , we shall use an adjust able component in order to locate the best band rejection frequency. Usually, the
bandwid t h of t he medical signal is low frequency; we, therefore, use a high-order low pass filter to suppress the high frequency band.
4.The sampling rat e of t he analog t o digit al conversion will decide t he resolu t ion of t he medical signal. The embedded circuit board is used to control the analog to digital converter, to receive the data of conversion, and to send out the digital data to the embedded circuit board.
B.Embedded Circuit Board
Our embedded circui t board is equipped wi t h t he embedded pla t form provided in a fully-fledged Linux development environment by leveraging t he generous, free, and open-sources in Linux world, in which we can focus on our applica t ions wi t hou t bo t hering wi t h low-level implement at ion det ails [12]. The embedded circuit board is built around a cost effect ive high performance ARM series microprocessor uni t t ha t provides comple t e in t erface architectures of software and hardware at a very low cost. A number of versatile applications on Linux can be applied t o t his plat form such as, FTP server, Web server, dat abase, IP forward, net work applicat ions, cont rols and communicat ion funct ions which are all easily implement ed on t his board. Wit h appropriat e expansion int erfaces, t his plat form can be readily connect ed t o an LCD module for furt her embedded product development.Finally, t his embedded circuit board can t ransmit t he digit al medical signal t o a remot e medical Web server by TCP/IP packet [9-10].
Fig. 3. The interface circuit board and embedded circuit board IO Port
connection.
IV.SOFTWARE MODULES
This embedded circui t board provides uClinux developmen environmen, which is a generous, free, and open source. Our sof t ware modules are separa t ed in t o embedded circuit board programming and remot e medical server programming. A.Programming of the Embedded Circuit Board
Fig. 4 shows he sof ware flowchar of our embedded circuit board for t he remot e medical measurement syst em. We use the ANSI C of our embedded platform development environment t o design t he cont rol program. This embedded plat form programming provides us wit h a very easy way of wri ing he con rol program. The major func ions of his program are t o collect t he ECG digit al dat a int o t he remot e medical server from the embedded circuit board through the Internet. In addition, our software modules can also store the digit al ECG signal dat a and display t he ECG on t he LCD display of t he embedded circui t board, and t ransmi t informat ion t o t he remot e medical server t hrough eit her t he Int ernet or wireless net works. During t he t ransmission, t he embedded circuit board can select t he server IP address t o locate the server computer. The basic operational steps of Fig.
4 may be briefly described as follows: (1) Load Operat ion System and reset the system; (2) Start the Boa web server; (3) Analog t o Digit al Conversion; (4) If Convert ed, finish; (5) Store the digital data to buffer; (6) If Continue, convert; (7) If Data buffer full; (8) Send the digital data from the socket to Internet; (9) Send finish and wait.
Fig. 4. The software flowchart on the embedded circuit board for the
ECG data collecting and sending.
The Software Flowchart of Embedded Circuit Board for the Remote Medical Measurement System (Fig .4)
(1)Load Operation System and reset the system.
(2)Start the Boa web server.
(3)Analog to Digital Conversion.
(4)If Converted, finish.
(5)Store the digital data to buffer.
(6)If Continue, convert.
(7)If Data buffer full.
(8)Send the digital data from the socket to Internet.
(9)Send finish and wait.
B.Boa Web server and CGI
We use he Web server o remo ely execu e he CGI program t o cont rol t he embedded circuit board. Three very important servers for an embedded system under uLinux are ht pd, t ht pd and Boa [13]. Such a server is based on t he HTTP pro t ocol (hyper t ex t t ransfer pro t ocol) and allows access via Web browser. By using such a browser, an on-line main enance or a remo e configura ion for an embedded system can be implemented. A graphical user interface (GUI) is oft en implement ed wit h t he help of a Web-server. We propose an implement at ion of a remot e Web server cont rol by active Web page. The Web server runs in the background and waits for connect attempts by clients. In our design, the Boa Web server is a single-t asking HTTP server, which is unlike a t radit ional Web server. It does not fork for each incoming connection, nor does it fork many copies of itself to handle mul t iple connec t ions, because t he uClinux is a derivat ive of Linux 2.0 kernel int ended for microcont rollers wi t hou t Memory Managemen t Uni t s (MMUs). This OS int ernally multiplexes all of the ongoing HTTP connections, and forks only for CGI programs, which must be separat e processes. In t he pursui t of speed and simplici t y, some aspects of Boa are different from the popular Web servers. In no part icular order, t he remot e host environment variable is no se for CGI programs. This is easily worked around because t he IP address is provided in t he remot e address variable, so t he CGI program ac t ually ge t s t he hos t by address ret urn or else a variant can be used. There are no server sides included in this Web server. The Boa Web server isn’t like the traditional Web servers, which are t oo slow to parse. Hence, he Boa Web server can be a much more efficient alternative.
C.Programming of the Remote Medical Information Server
We use t he sof t ware componen t s of a C++ sof t ware developmen t environmen t t o design t he Graphical User In erface (GUI) in he medical server for he embedded remot e ECG measurement syst em. This design provides us wit h a very easy met hod of learning t he execut ion result s. When a remote user opens the TCP/IP port and enables this medical server, t hen t he embedded circuit board will t ry t o connect to the medical server and transmit the digital medical da a o he remo e da abase by he In erne. The major func ion of he embedded circui board is o collec he medical measuremen t signal in t o t he remo t e medical informa t ion server and t hen our sof t ware can s t ore t he received signal in the medical database that can be displayed in the server through accessing either the Internet or wireless networks.
Fig. 5 shows t he soft ware flowchart of a remot e medical informa ion server. Firs, he sys em crea es a new form, resets the system, opens the TCP/IP port and selects the user numbers. If the system receives the medical information data, then it will store the data in the database and display the data waveform in the monitor.
Fig. 5. The software flowchart of remote medical information server
The Sof t ware Flowchar t of t he Remo t e Medical Information Server (Fig .5)
(1)Create a new form and reset the system.
(2)Open the TCP/IP Port.
(3)Select User Number.
(4)Yes or no receive the medical information data.
(5)Storage data in the database.
(6)Display the medical information data.
(7)Yes or no close the TCP/IP Port
V.EXPERIMENTAL RESULTS
Fig. 6 and 7 show the measurement interface circuit board and t he embedded plat form of our embedded remot e ECG measurement syst em. In t his design, we use some low-cost ICs o fulfil he basic func ions of he elec rocardiogram measurement syst em. The embedded circuit board cont rols he analog t o digit al convert er, and receives t he convert ed digital data, and sends out the digital data to the memory of
he embedded circuit board. In t he measurement int erface circuit board, t he high-order low pass filt er suppresses t he high frequency noise.
Fig. 6. The interface circuit board of the embedded remote medical
measurement system.
Fig. 7. The embedded circuit board of the embedded remote medical
measurement system.
The users or pat ient s can see t he ECG waveform bot h from t he LCD display of t he embedded circuit board at t he client sit e and from t he GUI int erface of t he client PCs by accessing the remote medical server system as shown in Fig.
8.
Fig. 8 shows t he GUI pict ure of t he embedded remot e ECG measuremen t sys t em, which provides t he basic funct ions of t he medical records such as, t he ECG signal viewing select ion, body t emperat ure and t he heart beat-rat e st at ist ics. By using t he Int ernet or wireless t o browse t he medical Web page the doctor can read the patient the medical information on the Web page from the Web server.
Table 1 shows the specification of our ECG measurement int erface circuit board. We set t he input resist ance at more t han 50MΩ, t he CMRR (common-mode-reject ion-rat io) 90 dB by an optimum adjustment, the bandwidth of ECG signal 1~200Hz, and t he power dissipat ion less t han 500mW. In addition, due to the bandwidth limitation of the ECG signal, wi t h a t ransmission ra t e of 144kbps t hrough a wireless network, we have demonstrated the real time transmission of t he remot e ECG signal t hrough eit her a wireless or a wire Internet.
Fig. 8.The GUI interface of the client PCs by accessing the remote
medical server system
Table I. The specification of our ECG measurement interface
circuit board
VI.CONCLUSIONS
The special pa ien s may need a medical measuremen sys t em t o moni t or one’s body condi t ion even if t ha t individual is not in a hospital. This paper proposes a design and implemen t a t ion of an embedded remo t e ECG measurement system. In the measurement interface circuits of embedded remot e ECG measurement syst em, we use some low-cost ICs t o fulfill t he basic funct ions of t he int erface hardware. The measurement interface circuits pick up a very weak ECG signal and provide amplificat ion, isolat ion and noise suppression. Our design also provides a fine-t uning
Body Temperature
Circuit
Analog to Digital Converter
ECG
Circuit Heart
Beat-Rate
Circuit
Body
Temperature
ECG Waveform
Etherne
t
Embedded
Circuit Board
mechanism, which has a minimum error rate. In addition, the embedded circui t board provides t he ECG buffering, displaying and network transmitting, which are supported by t he fully-fledged Linux developmen t environmen t. The embedded circuit board is lower in cost, smaller in size, and lower in power consumption than a PC. The embedded circuit board controls the analog to digital converter and through the expansion int erface inputs t he digit al dat a. We t ransmit t his digit al medical signal t o a remot e medical web server by TCP/IP packet. In addition, our software interface provides a friendly operat ion, Int ernet net work t ransmission modules, and a LCD displaying module at the client site for the remote embedded ECG measurement.
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