A Design of DSPIC Based ECG Signal Monitoringand Processing System

Noureddine BELGACEMBiomedical Engineering Laboratory

Abou Bekr Belkaid UniversityBP 230 Tlemcen, 13000

Email: ne belgacem@mail.univ-tlemcen.dz

Fethi BEREKSI-REGUIGBiomedical Engineering Laboratory

Abou Bekr Belkaid UniversityBP 230 Tlemcen, 13000

Email: f bereksi@mail.univ-tlemcen.dz

Abstract—The cardiovascular disease does harms to personshealth, and most of them are concerned with arrhythmia. So itis very important to detect the abnormal beats like arrhythmia.This paper presents a portable miniature wireless device forECG measurements. The ECG device is designed to be used invarious applications including measurement of heart rate duringphysical exercise and continuous long term measurement of ECGfor people assumed having, or being recovering from a cardiacdisease. The ECG device is wirelessly connected to a smart phoneor a computer using IEEE 802.15.1 based radio protocol. Thedevice sends the measured ECG signal together with additionalmeasurement parameters including body temperature and bloodpressure to mobile phone or computer, where the ECG signal canbe analyzed. The system contains a location based service (GPSmodule) to reconize and utilize a location of a person. A smallsize accelerometer was also integrated to give more informationabout body motion. This healthcare method is very important torespond to emergency rapidly by recognizing a patient’s location.

I. INTRODUCTION

According to the U.S. Food and Drug Administration(FDA), home healthcare is the fastest-growing segment ofthe medical device industry. Longer life spans, an increasingnumber of patients with chronic medical conditions, and risinghealth costs are the main forces behind the trend of immersingthe consumer home market with smarter and friendlier medicaldevices, Figure (1).

Fig. 1. The worldwide semiconductor market for medical electronics isincreasing, with a significant portion going into home medical products(source:Databeans Corp.)

For the management of various pathologies it can be veryimportant to monitor patient for long periods during his normaldaily activities. A continuous personal monitoring of chronicpatients can reduce hospitalisations and improve patients qual-ity of life; cardiac long monitoring (e.g. ECG) can help indiagnosis and identification of syncope and other paroxysmalarrhythmias; longterm patients activities monitoring can helpin elderly people management; combining cardiac activity(e.g. heart rate)and body-motion, patients physical activity andenergy expenditure can be estimated, Figure (2).

Fig. 2. ECG components and intervals.

It is also worth mention that continuous monitoring can helpin drive and regulate therapies and treatment (e.g. monitorblood glucose and insulin injection control). To accomplishthese tasks personal patients monitoring equipment have tocomply with some specific requirement: reduced dimension,portability and/or wearability (light weight, specific sensors,body compatibility etc.), long-term signals or parametersmonitoring (battery consumption, long-term electrodes, etc.),continuous signal acquisition and real-time processing andfeature extraction (A/D, microprocessors, SW, etc.), trans-mission capability (band, range, wireless, etc.), provide dataintegrity and security (communication protocols, identification,encryption, etc.), compliance with medical devices regulation(electrical safety, electromagnetic compatibility, etc.)[1].

Recently are becoming more and more available on marketwireless monitoring devices, such as hospital patient monitors,ambulance or portable equipments, some homecare devices

and, more in general, devices to be used in the every-daylife, which often use available telecommunication channels tocommunicate with external environment.

The wireless revolution is creating large numbers of newwireless devices with continuously more stringent require-ments: smaller size, weight, higher bandwidth and lower powerconsumption at an ever-decreasing cost. For these systems,on-chip integration of RF systems has become a reality. Inparticular, Bluetooth standard offers important advantages:lowcost, low EM interferences [2], reduced power consump-tion,confidentiality of the data, dimensions of the transmitterand it is capable of generate small pico-net of some devices.Also it is embedded in most of portable, palm computersand mobile phones and already used in a great number ofwearable devices (e.g. mobile phones wireless headsets). Theemerging Zig-Bee standard [3], [4] offers enhanced capabil-ities especially in term of power consumption, number ofconnected devices, etc. but, currently, it is not so widespreadas Bluetooth.

This paper describes a low cost, portable system with wire-less transmission capabilities for the acquisition, processing,storing and visualization in real time of the electrical activityof the heart to a mobile phone, a PDA or a PC, Figure (3).

Fig. 3. Mobile healthcare Framework.

Several groups have developed applications to monitor theECG in mobile devices, where the samples have been obtainedfrom standard databases [5], or they have development theECG module [6], [7]. Other works [8], [9] have proposedtechniques for signal processing via software to reduce noiseor classify heart pathologies. In this work we describe boththe implementation of the acquisition module with wirelesstransmission capabilities, the tool for real time ECG processingand visualization in mobile devices, and patient’s location.The structure is the following. In the following section systemarchitecture, employed technology and development environ-ment are described. In sections III and IV hardware andimplemented software will be explained in detail. Results andfinal prototype, together with the conclusions are shown insection V.

II. SYSTEM ARCHITECTURE

The system architecture can be seen in Figure 4, of whichthe protoptype encompasses the on-person platform. The over-all goal is to have viable context information processed onthe dsPIC and then sent to a smart phone in order to befurther aggregated and stored in a remote context managementinfrasctructure. Local processing is performed in order toabsract the received data from the Cardic circuit as well asreduce the overall wireless traffic in the system. As shownin other research [10], this will decrease the possibility ofcongestion on both wireless links in addition to the overallpower consumption of the system.

Fig. 4. System Overview.

A. ECG Acquisition

There are two forms of circuit for measuring ECG sig-nals. One comprises amplifier ICs, resistors and capacitors todesign a circuit board. The other uses ASIC to achieve themeasurement, and A/D converter and serial communicationports are integrated. In this design, we chose the CARDIC (p/nAuM441Cx), which is an integrated circuit developed mainlyfor the acquisition of electrocardiographic signals [11]. Thissingle chip permits the implementation of ECG systems withup to twelve leads. CARDIC is a low-power multisensor front-end acquisition system with on-board ADC (12bit@83KS/s)and serial interface communication protocol. It contains a fullyconfigurable multi-channel ECG block, front-end channels forblood pressure and body temperature signal processing, analogchannel for battery level monitoring and the possibility ofdirect access to the input of internal ADC through dedicatedpins.

B. ECG Processing

There are many microcontrollers used in ECG monitors,from 8-bit to 32-bit microcontrollers, as well as DSPs [12],[13]. In this design, we propose the use of dsPIC microcon-trollers (dsPIC30F6010), which are able to acquire and processthe signals needed in monitoring applications. Owing to the

cost-effectiveness of the devices, it is economically feasible toembed any number of them within a machine or process. In thesystem design, the speed of computation and memory capacityare considered as the two most important characteristics.Since the dsPIC30F6010 device has these properties, it hasbeen chosen for our design. This chip has the followingspecifications:• 30 MIPs processor speed• 10 bit ADC• 4 kbyte EEPROM• 8 kbyte SRAM• 144 kbyte program memory• 24 bit instruction bus• 16 bit data bus• 1 clock cycle DSP processing• Optimized instruction architecture with versatile address-

ing modesMicrochip MPLAB is used for software modules with C30

compiler.

C. Bluetooth Data TransmissionSeveral wireless technologies can be used to transmit ECG

signals, such as GSM/GPRS, Bluetooth, ZigBee, WLAN IEEE802.11, and so on [14], [15], [16], [17], [18]. In this proposalwe choose Bluetooth technology and other possibilitie can betested in future works.

To provide Bluetooth we choose BlueSmirf module pro-vided by Sparkfun Electronics [19]. It is a class 1 modelthat has an approximate range of 100 meters. The asyn-chronous data from the dsPIC microcontroller are deliveredto the BlueSmirf Bluetooth module on the serial port. TheBluetooth module is configured as a slave and the mobilephone is considered to be functioning as a master. The signalacquisition unit sends data to the Bluetooth module, whichtransmits data continuously, in blocks of ECG samples plustemperature reading and blood pressure. The data are sent asraw binary bytes.

D. Patient LocationIn a healthcare systemaccuracy of positioning is the most

important element regardless of costs, because the indoor errorshould be at least less then 1m to find an accurate location ofpatient [?]. A patient can move freely by putting on a sensor, Figure 5. His data measured by a sensor through a portableterminal such as a mobile phone is transferred to a remoteplace through CDMA or WLAN.

The transferred data are sent to a hospital and a doctorcan examine and manage a patients status. In addition, whenthe measured organism data is beyond a present value, animmediate contact is made to an emergency center to tracea patients location in order to be moved to hospital as soonas possible.

E. Body MotionTo get concise information about patient motion to esti-

mate physical activity a novel MEMS (MicroElectroMechan-ical Systems) 3-axes accelerometer was employed, Figure

Fig. 5. EM-406 GPS Module.

6. MEMS technology is based upon micromachined senseelements, usually silicon, to create moving structures. Me-chanical properties of silicon (stronger than steel but onlya third of the weight) combined with microelectronics allowelectrical signal generation by the moving structures. Typicallya MEMS accelerometer consists of interlocking fingers thatare alternately moving and fixed. Acceleration is sensed bymeasuring the capacitance of the structure, which varies inproportion to changes in acceleration. A capacitive approachallows several benefits when compared to the piezoresistivesensors used in many other accelerometers. In general, gaseousdielectric capacitors are relatively insensitive to temperature.Although spacing changes with temperature due to thermalexpansion, the low thermal coefficient of expansion of manymaterials can produce a thermal coefficient of capacitanceabout two orders of magnitude less than the thermal resistivitycoefficient of doped silicon. Capacitance sensing therefore hasthe potential to provide a wider temperature range of operation,without compensation, than piezoresistive sensing. Moreover,most of the available capacitive sensors allows for response toDC accelerations as well as dynamic vibration. These charac-teristics of MEMS capacitive accelerometer sensor combinedwith their extremely tiny dimension (few mm) and light-weight(few grams), their low power consumption made such sensorsa convenient choice for personal biomedical devices design.

Fig. 6. Accelerometer Module.

III. MOBILE UNIT APPLICATION SOFTWARE

The software developed can be divided into two programs:a program associated to the microcontroller, and the second isfor the applications in the mobile phone.

A. Microcontroller Software

The microcontroller has been programmed to perform thefollowing functions: capture and digitize the ECG signal from

the ECG ASIC, establish the connection to the Bluetoothphone and send the data. This Bluetooth module allows pro-vides an API for communication through the AT level, freeingthe programmer from implementing the complete Bluetoothstack.The following submodules constructed the main softwaremodule:• ADC program• Filter application program• FFT program• Graphic LCD program (optional)• Sending data program (Bluetooth)• GPS module information reading program• Acceleromter reading program

B. Mobile Phone Software

The application for embedded devices, such as mobilephones or PDAs, offers a service in the SPP port via Bluetooth.It will allow us to monitor the patients ECG in real-time. Themobile device can be used as a client or as a server dependingon the operation mode. When the medical staff requires ECGdata on demand, the mobile device operates as a client. Onthe other hand, when alarm condition comes up, the wearabledevice can start the communication with the mobile terminal.

The application has been Developed using the Java platformfor embedded devices, J2ME. The Bluetooth communicationwas programmed using the Bluetooth API. Binaries wereobtained using the J2ME Wireless Toolkit [20]. The softwareapplication takes the received bytes from the buffer and plotsthe ECG samples, displaying the body temperature and theblood pressure.

IV. CONCLUSION

In this paper, we presented the design of a mobile personalelectrocardiogram monitoring system with patient location andmotion. An ECG signal acquisition circuit was integrated ina module that communicates with a smart mobile phone viaBluetooth. Application software running on the smart phonewas also developed to receive and plot ECG signals anddisplay body temperature and blood pressure with patientlocation. Currently we are testing this system.

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