Ecg Acquisition Unit

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ECG ACQUISITION UNIT

SEMINAR REPORTsubmitted in partial fulfillment of the requirements for the award of the

degree of

Bachelor of Technology

inELECTRONICS AND COMMUNICATION ENGINEERING

of

MAHATMA GANDHI UNIVERSITY

by

TESS THOMAS(201061)

Department of Electronics and Communication EngineeringRajagiri School of Engineering and Technology

Rajagiri Valley, Kakkanad, Kochi, 682039

2012


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Rajagiri Valley, Cochin - 682 039

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

CERTIFICATE

Certified that this document titled ECG ACQUISITION UNIT is a bonafide report ofthe seminar presented by TESS THOMAS (201061) of seventh semester Electronics andCommunication Engineering in partial fulfillment of the requirements for the award of degree of

Bachelor of Technology in Electronics and Communication Engineering of the Mahatma Gandhi

University, Kottayam, during the academic year 2012-2013.

Seminar Guide Head of Department

Ms.Tressa Michael Mr.Jaison Jacob

Place: Kakkanad

Date:


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ACKNOWLEDGEMENTS

I bring out the report of my seminar work endeavoring my biggest gratitude to GOD almighty.I would like to extent my sincere gratitude to Prof. Jaison Jacob, Head of the Department ofElectronics and Communication, for equipping me with all facilities during the development ofmy report.

I make use of this opportunity to express my heartily gratitude to my project co-coordinatorsMr.Jobin K Anthony, Associate Professor in Electronics and Communication Department andMr. Rama Varma, Asst. Professor in, Electronics and Communication Department, withoutwhose help I would have been far from completion of this prototype and assisting me in timesof needs and also to my project guide Ms.Tressa Michael, Asst. Professor in Electronics and

Communication department, for giving me relevant ideas and advises for making my project agrand success. I am also thankful to the Lab Assistants, the Library staffs and all the membersof the faculty of the college for their whole hearted support and guidance.

This acknowledgement will not stand if my friends and classmates are not thanked whoseconstant encouragement and timely criticism helped me a great extend and fueled my determi-nation. I take this opportunity to thank all who have helped me directly or indirectly throughthis endeavour.


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ABSTRACT

The monitoring of vital physiological signals has proven to be one of the most efficient waysfor continuous and remote tracking of the health status of patients. Electrocardiogram monitorsare often used in many medical service centers and hospitals to diagnose and monitor a personshealth status by measuring their cardiac activity. An ECG signal, which can be utilized toevaluate the hearts electrical activity, measure the rate and regularity of heartbeats, the positionof the chambers, identify any damage to the heart and investigate the effect of drugs anddevices used to regulate the heart. This procedure is very useful for monitoring people with (orsusceptible to) impairments in their cardiac activity.This report presents a development platform of an ECG acquisition unit, capable of capturingcardiac data in digital format and transmitting ECG signals via any wireless technology to aPC or set-top box.

This development will make ECG data more: prolific, easy to obtain, and effective. It can beused to provide heart patients with home based monitoring facility or it can be used in hospitalpremises to efficiently monitor ECG without compromising patient mobility due to wires etc.Also, it can be used to centrally monitor the data in a nursing room type of facility instead ofvisiting each room and checking the respective monitors.


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List of Figures

2.1 Block Diagram Of ECG Acquisition Unit. . . . . . . . . . . . . . . . . . . . . 22.2 Hardware Block Diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

3.1 Electrical Impulse Of The Heart. . . . . . . . . . . . . . . . . . . . . . . . . . 4

4.1 Recessed Electrode Structure. . . . . . . . . . . . . . . . . . . . . . . . . . . 64.2 Right Leg Driver Topology.. . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

5.1 Shematic Diagram Of An Instrumentation Amplifiers . . . . . . . . . . . . . . 105.2 60 Hz Notch Filter Response . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

6.1 ADC Result Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136.2 External Data Memory Interface (16Mbytes Address Space). . . . . . . . . . . 14

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Contents

Acknowledgements i

Abstract ii

List of Figures iii

1 Introduction 1

2 Design Of ECG Acquisition Unit 22.1 Basic Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.2 Basic Block Diagram Description . . . . . . . . . . . . . . . . . . . . . . . 22.3 Hardware Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32.4 Factors In The Design Of ECG Acquisition Unit . . . . . . . . . . . . . . . 3

3 ECG Signal Source 43.1 ECG Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

4 Sensor Design Considerations 64.1 Electrodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64.2 Noise Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

4.2.1 AC mains inteferance . . . . . . . . . . . . . . . . . . . . . . . . . . 74.2.2 Biological Noise Sources . . . . . . . . . . . . . . . . . . . . . . . . 7

4.3 Noise Reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74.3.1 Signal Filtering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74.3.2 ECG Right Leg Driver . . . . . . . . . . . . . . . . . . . . . . . . . 74.3.3 Twisted Pair Cables And Shielded Cables . . . . . . . . . . . . . . 8

5 Signal Acquisition Hardware Design 95.1 Electrodes And Electrode Placement . . . . . . . . . . . . . . . . . . . . . 95.2 Instrumentation Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . 95.3 Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

5.3.1 Low Pass Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105.3.2 Notch filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

6 Digitisation 136.1 Data Buffering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

7 Conclusion 16

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8 Future Considerations 178.1 ECG Signal Acquisition from Individually Measured Electrode Potentials . 178.2 Signal Compression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

References 18


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Chapter 1

Introduction

An ECG is a measurement of the electrical activity of the heart (cardiac) muscle asobtained from the surface of the skin. As the heart performs its function of pumping

blood through the circulatory system, a result of the action potentials responsible for themechanical events within the heart is a certain sequence of electrical events. It measuresthe rate and reguarity of heart beat. ECG acquisition unit is a mobile hardware deviceattached to the patient whose purpose is to collect the ECG signal from the patientand send it to central unit wirelessly. This provide heart patients with home basedmonitoring facility or it can be used in hospital premises to efficiently monitor ECGwithout compromising patient mobility due to wires etc. Also, it can be used to centrallymonitor the data in a nursing room type of facility instead of visiting each room andchecking the respective monitors.

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Chapter 2

Design Of ECG Acquisition Unit

2.1 Basic Block Diagram

Figure 2.1: Block Diagram Of ECG Acquisition Unit.

2.2 Basic Block Diagram Description

An ECG signal is a quasi-periodical rhythmically repeating signal which intrepretsthe electrical activity of the heart.these signals are extracted out from the body usingsilver-silver chloride electrodes.The ecg signal is picked from the surface of skin(wherethe electrodes are placed)via the electrode gel and sensor.The signal obtained from the

electrodes is very small in magnitude(mv)so it is passed to a amplification unit wherethe amplifiers boost the level of the input signal th match the requirements of the record-ing/display system or to match the range of the analog to digital convertor, thus increasingthe sensitivity and resolution of the measurement.

The amplified signals are passed to the filtering unit. A filter is a circuit which amplifiessome of the frequencies applied to its input and attenuates others. Additionally filters areused to reject the unwamted noise within a certain frequency range.

The final stage is the analog to digital conversion and buffering stage.In this the analog

signals(ECG)are converted to digital format using microcontroller which has in built ana-log to digital converter. The transmission of data on wireless IP network has many latencyissues. Many samples are lost while packets are being transmitted on network.this results

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in severe distortion when recreating the orginal signal.So data buffering is used inorder toprevent the loss of data while transmitting. Microcontoller does the data buferring also.

Now the ECG signal from the body is ready to be transmitted wirelessly to a central

unit.

2.3 Hardware Block Diagram

Figure 2.2: Hardware Block Diagram

2.4 Factors In The Design Of ECG Acquisition Unit

The major factor taken into consideration when designing the ECG acquisition systemis the nature of the ECG signals itself. The useful bandwidth is described as rangingfrom 0.5 Hz to 35 Hz for monitoring applications and between 0.05 Hz and 150 Hz fordiagnosis applications. The ECG signal is extremely weak (up to 2 mV) combined witha variable electrode-skin contact potential in the order of a few hundred millivolts (causeof baseline wander), and a common-mode DC component of up to 1 V. On top of thisthe signal contains noise from power line interference, muscle movement and respiration.Because this system is targeted at monitoring rather than clinical analysis of the ECG,the 0.535 Hz useful bandwidth was considered. For such monitoring systems a single leadmonitoring is sufficient.

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Chapter 3

ECG Signal Source

In the resting state, cardiac muscle cells are polarized, with the inside of cell negativelycharged with respect to its surroundings. The charge is created by different concentrations

of ions such as potassium and sodium on either side of the cell membrane. In responseto certain stimuli, movement of these ions occurs, particularly a rapid inward movementof sodium. In this process of depolarization, rapid loss of internal negative potentialresults in an electrical signal. The mechanism of cell depolarization and repolarizationis used by nerve cells to carry impulses and by muscle cells for triggering mechanicalcontractions. This results in generation of an electrical impulse which can be acquired byputting electrodes on specific points of the body.

Figure 3.1: Electrical Impulse Of The Heart.Stage 0 = depolarization, opening of voltage gated sodium channels

Stage 1 = initial rapid repolarization, closure of sodium channels and chloride influxStage 2 = plateau opening of voltage gated calcium channels

Stage 3 = repolarization, potassium effluxStage 4 = diastolic pre potential drift.

Figure 3-1, shows the potential signals and the stages. This does not look like the

signal from an ECG sensor. The reason is that the electrical signal will spread to differentparts of the body in different ways. This is why the number of leads on an ECG sensoris important. Different forms of disease can be diagnosed from different leads. The most

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common lead is lead II, which is the lead implemented in this sensor. Lead II is definedas the lead between the right and left arms.

The standard for diagnostic ECG is twelve leads, however for portable systems, one

EKG lead (usually lead II) can be used. Lead II can diagnose the more common diseaseslike arrhythmias.

3.1 ECG Measurement

The electrical impulses within the heart act as a source of voltage, which generatesa current flow in the torso and corresponding potentials on the skin. The potentialdistribution can be modeled as if the heart were a time-varying electric dipole. If twoleads are connected between two points on the body (forming a vector between them),electrical voltage observed between the two electrodes is given by the dot product of the

two vectors. Thus, to get a complete picture of the cardiac vector, multiple referencelead points and simultaneous measurements are required. An accurate indication of thefrontal projection of the cardiac vector can be provided by three electrodes, one connectedat each of the three vertices of the Einthoven triangle. The 60 degree projection conceptallows the connection points of the three electrodes to be the limbs.

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Chapter 4

Sensor Design Considerations

The front end of an ECG sensor must be able to deal with the extremely weak natureof the signal it is measuring. Even the strongest EcG signal has a magnitude of less

than 10mV, and furthermore the ECG signals have very low drive (very high outputimpedance). The requirements for a typical ECG sensor are as follows:

Capability to sense low amplitude signals in the range of 0.05-10mV.

Very high input impedance, greater than 5 Mega-ohms.

Very low input leakage current, less than 1 micro-Amp.

Flat frequency response of 0.05-150 Hz.

High Common Mode Rejection Ratio(CMRR).

4.1 Electrodes

Electrodes are used for sensing bio-electric potentials as caused by muscle and nervecells. ECG electrodes are generally of the direct-contact type. They work as transducersconverting ionic flow from the body through an electrolyte into electron current andconsequentially an electric potential able to be measured by the front end of the ECGsystem. These transducers, known as bare- metal or recessed electrodes, generally consistof a metal such as silver or stainless steel, with a jelly electrolyte that contains chloride

and other ions.

Figure 4.1: Recessed Electrode Structure.

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On the skin side of the electrode interface, conduction is from the drift of ions as theECG waveform spreads throughout the body. On the metal side of the electrode, conduc-tion results from metal ions dissolving or solidifying to maintain a chemical equilibriumusing this or a similar chemical reaction:

Ag Ag+ +eThe result is a voltage drop across the electrode-electrolyte interface that varies de-

pending on the electrical activity on the skin. The voltage between two electrodes is thenthe difference in the two half-cell potentials.

4.2 Noise Sources

There are four principal noise pick up or coupling mechanisms for noise conductive, ca-pacitive, inductive, and radiative.

4.2.1 AC mains inteferance

The 60 Hz mains power-line frequency and its components are the most common sourceof interference in a biomedical signal. AC interference is coupled into the system frompower-line and devices using AC power such as lamps. The coupling mechanism can beeither capacitive or magnetic, but the capacitive mechanism is the more prevalent. The60 Hz noise is common to all points on the patient, but the 60 Hz noise is additive to theECG signal and is in the order of tens of volts.

4.2.2 Biological Noise Sources

When an electrode comes in contact with skin, a potential difference up to 300mV appearsknown as baseline wander. This can be made worse by poor connection of electrodes,perspiration or the movement of electrodes due to respiration. Any movement that causemuscle utilization generates noise that interferes with ECG signal. This is specially thecase when limb leads are used. The best ECG signal is obtained when the patient isat rest and relaxed. Also, skin preparation to remove any non-conductive substance isimportant in obtaining a strong ECG signal.

4.3 Noise Reduction

4.3.1 Signal Filtering

The presence of noise gives rise to the need to signal filtering. Noise can be removedthrough the use of analogue circuitry or digital signal processing. Due to the weak natureof ECG signal and the noise affecting it requires that a range of filters be implemented.

4.3.2 ECG Right Leg Driver

ECG right leg driver is implemented to eliminate the common mode noise generated fromthe body. The system is shown in figure 4.2. The two signals entering the differentialamplifier are summed, inverted and amplified in the right leg driver before being fed back

to an electrode attached to the right leg. The other electrodes pick up this signal andhence the noise is cancelled.

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Figure 4.2: Right Leg Driver Topology.

4.3.3 Twisted Pair Cables And Shielded Cables

Use of twisted pair or shielded cable is recommended in obtaining a noise free signal.Due to the geometry of twisted pair wires and electromagnetism, the noise signals areinduced with equal magnitudes, but in opposite polarity. This causes a cancellation ofthe noise signals.

Also, the introduction of shield or ground braid in the cable can be used to isolate the

cable signal leads from radio frequency interference and electromagnetic interference.

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Chapter 5

Signal Acquisition Hardware Design

The circuitry able to obtain an ECG signal in a largely traditional manner was built. Theblock diagram depicting each stage of the signal acquisition hardware can be found in

Block 2.

5.1 Electrodes And Electrode Placement

Disposable self-adhesive electrodes were used in the experiments. Also, AgCl conductinggel was used for stronger signal capture. As a general principle, the closer the electrodesare to the heart, the stronger the signal that will be obtained. In our lead II formation,electrodes were placed on the right arm and left leg with right leg acting as the groundfor the body.

5.2 Instrumentation Amplifier

The differential amplifier is well suited for most of the applications in biomedical mea-surements. However, it has the following limitations:

The amplifier has a limited impedance and therefore, draws some current from thesignal source and loads them to some extent.

The CMRR of the amplifier may not exceed 60 dB in most of the cases, which isusually inadequate in modern biomedical instrumentation systems.

The limitations have been overcome with the availability of an improved version of thedifferential amplifier, which is the instrumentation amplifier.An instrumentation ampli-fier is a precision differential voltage gain device that is optimized for operation in anenvironment hostile to precision measurement. It basically consists of three op-amps andseven resistors. Basically connecting a buffered amplifier to a basic differential amplifiermakes an instrumentation amplifier.

The instrumentation amplifier offers the following advantages for its applications inthe biomedical field.

Extremely high nput impedance.

Low bias and offset currents. Less performance deterioration if source impedance changes.

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Possibility of independent reference levels for source and amplifier.

Very high CMRR.

High slew rate.

Low power consumption.

Good quality instrumentation amplifiers have become available in single IC form such asICL7605, LH0036, etc.

Figure 5.1: Shematic Diagram Of An Instrumentation Amplifiers

5.3 Filter

A filter is a circuit which amplifies some of the frequencies applied to its input andattenuate others.there are four common types:high-pass,which only amplifies frequenciesabove a certain value; low pass, which only amplifies frequencies below a certain value;band pass which only amplifies frequencies within a certain band; and band stop,whichamplifies all frequencies except those in a certain band.

Filters may be designed using many different methods. These include passive filterswhich use only passive components, such as resistors, capacitors and inductors. Activefilters use amplifiers in addition to passive components in order to obtain better perfor-mance, which is difficult with passive filters.Operational amplifiers are frequently used asgain blocks in active filters. Digital filters use ADC to convert a signal to digital formand then use high-speed digital computing techniques for filtering.

5.3.1 Low Pass Filter

First stage in the filtering unit is a low-pass filter designed at the cut-off frequency of150Hz. The low-pass filter was implemented as cascaded RC, or passive filters. At highfrequencies, the opamp, whose output is limited to its slew rate or maximum frequency ofoutput, may not be able to cope with the high frequency of the signal. For this reason it

was chosen to implement this filter as cascaded RC filters, before isolating the filter fromthe rest of the circuit by a voltage follower. The cut-off frequency is calculated by theequation,

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fc= 1

2RC (1)

At the cut-off frequency of the first filter, the attenuation will be 20dB/decade (fc 10). Atthe cut-off frequency of the second filter, the attenuation will be 40dB/decade thereafter.

If the two cut-off frequencies are equal, then the slope will be 40dB/decade from thecommon cut-off frequency.The second stage of the amplifier presents a load to the firststage, for this reason the second stages impedance should be higher than that of the firststage.low pass filter ussed is of non-inverting and has a gain of unity.

5.3.2 Notch filter

Notch filters, also commonly referred to as band stop or band rejection filter. Theyare designed to transmit most wavelenghts with little intensity loss while attenuating aspecific frequency range. They are basically the inverse of band pass filters.notch filterscan be easily made with a slight variation on all pass filter, the pole and zero have

equal(logarithmic) relative distances from the unit circle. All we need to do is put thezero closer to the circle. Then the frequency at which zero is located is exactly cancelfrom the spectrum og input data. Most common example of a notch filter is 60-Hz noisefrom power lines.Notch filters are band stop filters with high Q factor. The twin T notch filter usingopamps is a simple circuit that can provide good level of rejection at notch frequency.At f = fNOTCH, the output goes to zero. Figure shows the response plot for the circuitshown above where fo = 60 Hz and Q = 6.

Figure 5.2: 60 Hz Notch Filter Response

The notch frequency for the notch filter is set by the following calculations:

f= ALP

AHP RZ2

RZ1 fo (2)

ALP = Low pass outputAHP = High pass output

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Typically, ALP / AHP = 1 and RZ2 / RZ1 = 1 which means f = fo. Notch filter playsan important role in getting rid of the AC mains signal interference through the humanbody. If successfully implemented, it will pass clean ECG signal at its output.

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Chapter 6

Digitisation

The recent progress of digital technology in terms of both hardware and software makesmore efficient and flexible digital data rather than analog processing. Digital techniques

have several advantages.Their performance is not affected by unpredictable variable suchas componenet aging and temperature which can degrade the performance of analogdevices. Moreover, design parameters can be more easily changed because they involvesoftware other than hardware modification. The ADC requires the signal for sampling tobe contained completely in the positive voltage domain.in order to make it completely inthe positive domain summing amplifier is used before digitization.

Microcontroller which as inbuilt ADC is used to manage the digitization of the ECGsignal and subsquently store it in readiness for transmission. Generally most of the micro-controllers has built in 12-bit ADC which is used for digitization. The ADC has 8 channels

and is configurable via 3-register (ADCCON1, ADCCON2 and ADCCON3) Special Func-tion Register (SFR) interface. The analog input voltage range is from 0V to VREF whichis set to be 9V in the prototype system. Once configured through ADCCON1-3 SFRs,the ADC will convert analog input and provide a 12-bit result into ADCDATAH/L SFRs.The format of the result bits is shown in figure 6.1.

Figure 6.1: ADC Result Format

Due to latency issues involved in wireless transmission on IP network (using 802.11b),the sampling rate has to be fairly low when compared to clinical system, which samples

at 1 kHz. In a telemetry system, the sampling frequency is typically much lower with thesampling frequency of 400Hz implemented in this system acceptable. This is more than

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the Nyquists criteria for sampling rate. The data resolution has not been compromisedso as to create an accurate signal out of the sampled data.

6.1 Data Buffering

The transmission of data on the wireless IP network has many latency issues. Therefore,many samples are lost while the packets are being transmitted on the network. This resultsin severe distortion when recreating the original signal. It becomes very critical to designthe system in a way that samples are not lost while the data is being transmitted on thenetwork. Thus, a data buffering strategy was designed to overcome this limitation.A buffer space was introduced in the system to hold data for 5 seconds (at least in orderto show sufficient sections of the waveform for analysis). The ADC results are storedin the buffer locations using pointer arithmetic. Once the buffer is full, it is ready fortransmission. A signal is sent to the transmission module to start transmission. To avoid

over-writing the buffered data, the ADC is halted while the transmission takes place ofthe 5 second buffered data. Once the transmission is complete, the ADC starts conversionagain and this process continues as long as the system stays powered on. The digitizationof the analog inp ut takes place at a rate of 400samples/sec. Each sample is 12-bitwhich takes 2 bytes of space for storage. It has 4kB of EEPROM space for data storagewhich is built on-chip. The tests for storage of data on this space didnt produce accurateresults due to slow access speed of the ROM (380?s for writing 4 bytes as a page). Manysamples were lost and accurate signal could not be reproduced. The ADuC831 providesfor external memory interfacing up to 16MB. A high-speed nonvolatile SRAM was tested.The results produced by external RAM interfacing were much better and accurate than

the EEPROM. Therefore, it was decided to use the external RAM instead of the internalEEPROM.

Figure 6.2: External Data Memory Interface (16Mbytes Address Space)

The Port 0 (P0) acts the multiplexed address/data bus. It emits the low byte of the

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data pointer (DPL) as an address, which is latched by a pulse of ALE prior to data beingplaced on the bus by the ADUC831 (write operation) or the SRAM (read operation).Port 2 (P2) provides the data pointer page byte (DPP) to be latched by ALE, followedby the data pointer high byte (DPH). If no latch is connected to P2, DPP is ignored

by the SRAM and the 8051 standard of the 64kBytes external data memory access ismaintained.

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Chapter 7

Conclusion

This report presents a development platform of an ECG acquisition unit, capable ofcapturing cardiac data in digital format and transmitting ECG signals via any wireless

technology to a PC or set-top box. The monitoring of vital physiological signals has provento be one of the most efficient ways for continuous and remote tracking of the health statusof patients. Electrocardiogram monitors are often used in many medical service centersand hospitals to diagnose and monitor a persons health status by measuring their cardiacactivity. An ECG signal, which can be utilized to evaluate the hearts electrical activity,measure the rate and regularity of heartbeats, the position of the chambers, identify anydamage to the heart and investigate the effect of drugs and devices used to regulatethe heart. This procedure is very useful for monitoring people with (or susceptible to)impairments in their cardiac activity.

This development will make ECG data more: prolific, easy to obtain, and effective.

It can be used to provide heart patients with home based monitoring facility or it canbe used in hospital premises to efficiently monitor EKG without compromising patientmobility due to wires etc. Also, it can be used to centrally monitor the data in a nursingroom type of facility instead of visiting each room and checking the respective monitors.

An ECG signal is a quasi-periodical rhythmically repeating signal which intrepretsthe electrical activity of the heart. These signals are extracted out from the body usingsilver-silver chloride electrodes. The signal obtained from the electrodes is very small inmagnitude(mv)so it is passed to a amplification unit where the amplifiers boost the levelof the input signal to match the requirements of the recording/display system or to matchthe range of the analog to digital convertor, thus increasing the sensitivity and resolutionof the measurement.

The amplified signals are passed to the filtering unit. A filter is a circuit which amplifiessome of the frequencies applied to its input and attenuates others.additionally filters areused to reject the unwamted noise within a certain frequency range.

and finally using a ADC the signals are converted to digital format and is ready forthe wireless transmission. The ECG acquisition unit thus acts as a bridge between thesensor which is used to extract signals from body and wireless transmission. only if theacquisition unit is included the signals recieved at the recieving end will be exact as theECG signal from the body.

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Chapter 8

Future Considerations

It is evident that a lot of work and improvements in all facets of the system are requiredbefore the ultimate goal of a miniature completely wireless ECG system can be reached.

Some of the more important improvements are discussed here.

8.1 ECG Signal Acquisition from Individually Measured Electrode Poten-tials

The instrumentation amplifier has very high CMRR. The noise that is common to bothelectrodes attached to the body has much greater amplitude as compared to the actualECG signal. It is the instrumentation amplifier that rejects the common noise having highCMRR and only amplifies the actual ECG signal. If the ECG signal becomes common toboth electrodes, it is also rejected due to the high CMRR of the instrumentation amplifier,

thus, resulting in either no or a very weak output of the instrumentation amplifier. Itis recommended that an investigation into what type of material there is that can formand equivalent electrode that is unable to pick the ECG but is able to pick up the noisecoupled to the body be conducted. This will make noise common to both electrodes whilethe ECG will be conducted by only one of them.

8.2 Signal Compression

It is recommended to use signal compression once the EKG signal is digitized. Thiswill reduce the memory footprint of the stored ECG data and also reduce the networktraffic while transmission. However, special algorithms should be used in order to avoidany loss of resolution while compressing and decompressing.

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References

[1] R S KHANDPUR Biomedical Instrumentation.

[2] Dale Dubin, M.D.Rapid Interpretation of EKGs.

[3] Chou Electrocardiography in Clinical Practice Adult and Pediatric.

[4] Bronzia,Joseph D,IEEEE Press,20000 The Biomedical Engineering Handbook.

[5] Ovidiu Apostu,Bogdan Hagiu,Member IEEE Wireless ECG Monitoring.

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