e991x02.pdf

The project is an advanced electrocardiograph with

a much greater accuracy than the electrocardio-

graphs used in most of the world’s hospitals today.

Remarkably, the project allows patients to record their

own ECG at home, and send the relevant data to

the doctor’s office by modem.

By Jack and Mark Nowinski

electrocardiograph

International First Prize

always be ongoing on account of the

software, which has the ability to cre-

ate databases for people (patients)

using

electrocardiograph

The project, which involves both hard-

ware and software, covers all the three

themes of the International PC

Software Competition: measurement ,

development , and communications .

The software is the most instrumental tool

used in the project on account of the

high accuracy it achieves through the

use of signal transforms and real-time

processing of the electrocardiogram

signal supplied by the hardware unit.

As for the first theme, measurement ,

the software program is able to graph

and analyze the full signal spectrum

coming from the hardware unit.

Through this analysis of the signal, the

software program is able to measure

very critical aspects of the electrocar-

diogram (ECG) such as the QRS com-

plex, the frequency of the heartbeat

and the number of beats per minute

(no electrocardiograph in the world

has such a feature built into one

device). Due to the powerful instruc-

tion set of fourth and fifth generation of

Intel x86 processors, the mathematical

transforms used for the measurement

of the signal enable the most accu-

rate electrocardiograph in the world

to be created.

This project is full of development ; first-

ly the hardware and software were

designed and developed from

scratch. A lot of development tasks

took place both on the software and

the hardware. Development will

described here.

Also, the hardware is has been

designed to be expandable, and soft-

ware function routines are provided to

detect if the PC processor has MMX

instructions for future portability and

compatibility. In that way, the project

can always take full advantage of the

processor when needed.

As for communication there are two

ways this project communicates with

the outside world, (1) through a printer

port (parallel port), and (2) through a

modem. The control program commu-

nicates with the electronic hardware

via the printer port in which data is sent

rapidly in a bi-directional fashion

between the computer and the elec-

tronic hardware. Through the printer

port the software is able to control the

entire electronic hardware. The sec-

ond way in which the program com-

municates with the outside world is

through a modem. The project is pri-

marily intended to be used by people

in their homes. A heart patient with a

computer at home would apply the

standard medical electrodes to his/her

body and be able to transmit his/her

ECG to a doctor’s office so the doctor

would then be able to study the ECG

and determine if medical help is

needed. The ECG signal can be trans-

mitted in real-time over the modem

and accurate up-to-date information

can then be processed by a medical

doctor, the software program itself has

the capability for medical analysis.

2 - 1/99 Elektor Electronics EXTRA ——————————————— PC T OPICS

the

The program

The software used to produce or com-

pile the software was Borland C++

version 5.01 (with in-line assembly).

The software program is based around

a graphical-user-interface (GUI) of the

authors’ own design, see Figures 1a-

d . All software operations take place

mainly in the menu on the left-hand

side of the screen and some measure-

ment specific operations take place in

the graphing window. The function of

the software program is to graph an

ECG on the screen and if necessary

transmit it to a doctor’s office (the doc-

tor would have to be using the elec-

trocardiograph software program to

receive the ECG signal). The program

is able to receive data from two chan-

nels (more can be added, but for stan-

dard medical and home use one/two

channel(s) are sufficient). Both chan-

nels can be displayed at the same

time, while one may be detecting the

so-called QRS complex in the ECG, the

other can detect other arrhythmia’s.

Another first for an electrocardiograph

is the use of a TIME BASE for an accu-

rate interpretation and analysis of the

ECG signal. The other options, X-MAG,

TRIGGER, MODEM and FILE are

described in the interactive multime-

dia presentation on the CD-ROM sup-

plied (see end of article). To summa-

rize, the X-MAG even further divides

the time base setting by constant inte-

ger dividers, the TRIGGER control but-

ton sets the triggering level and

MODEM control button initializes the

modem (along with the telephone

number to be called) and tells the pro-

gram to transmit the ECG over the tele-

phone line. In FILE you can open and

save ECG files and thus help to build a

database that could be used in the

future by a medical doctor. The entire

graphics library used by the program

had to be written from scratch, and

the authors also had to configure the

interrupts for the printer port and initial-

ize various types of modems and their

protocols. In summary, the function of

the software program is to graph

incoming ECG signals (from the hard-

ware unit through the printer port), and

perform a very intense analysis of the

signal and finally save the waveform

and/or transmit it to a doctor’s office;

the software program measures the

ECG signal, develops a database,

and communicates with the outside

world by transmitting the signal to a

medical facility.

Figure 1a. This screenshot has the ECG waveform already plotted. The control buttons on the left manipulate how the incoming ECG

signal is processed. For example, by clicking the right or left mouse button you can increase or decrease the time base on the grid.

Figure 1b. This screenshot is like the one above but has the measurement feature activated. The time base (lower right) is a factor

when calculating the exact time (delta t).

Figure 1c. This screenshot shows the program operating under a different time base (100.0 msec/div).

Figure 1d. Measurement results for the image above. Notice that the peaks are farther apart on screen but the time base is utilized to

produce an accurate measurement.

PC T OPICS ——————————————— Elektor Electronics EXTRA

3 - 1/99

transducer

60 Hz

(50 Hz)

Active

Notch

input

+12V

-12V

ECG

Preamp

HP LP

BATT.

DC - DC

Converter

A - D

CLK

SSO

CLK

SSO

CH0

+12V

-12V

CH1

LPT

Interface

3...16V

992010 - 11

Figure 2. Block diagram of the electrocardiograph hardware.

The hardware

designed and incorporated because

certain integrated circuits require neg-

ative and higher voltages other than

standard TTL voltages.

An analogue-to-digital converter (12-

bit) is used to digitize the analogue

ECG signal into the digital domain so

the software program along with PC

will be able to recognize it, this also

improves the analysis of the signal

later in the program. Opto-isolators

are used to send the digitized signal

from the hardware to the computer via

the printer port (LPT); opto-isolators are

need in this type of medical equip-

ment to isolate the hardware supply

voltage from that of the computer.

Unfortunately, owing to lack of space it

is not possible to produce all schemat-

ics and PCB artwork for the hardware

developed by the authors. The circuit

diagram of the ECG input amplifier is,

however, given as a sample in

Figure 3 . The inputs of this circuit are

connected to standard ECG elec-

trodes as demonstrated in Jack and

Mark’s wonderful video clip in which

they describe the development and

basic operation of their project. Well

worth viewing!

As shown by the block diagram in

Figure 2 , the hardware is composed

of amplifiers, active filters, an ana-

logue to digital converter, opto-isola-

tors, and a DC/DC converter and

inverter. A highly accurate low-pass

and high-pass filter combination

(active Butterworth Fourth-order filter)

was designed and produced to elimi-

nate the extraneous noise produced

by power lines and skin movements

under the electrodes. The filter combi-

nation has an extremely high roll-off

rate thus making sure that the required

frequencies are accepted and other

unwanted frequencies are rejected. A

DC/DC converter and inverter were

(992010)

All software, source code files, schematic

files, PCB artwork files and a demonstration

video (AVI file) as supplied by the authors

may be found on a CD-ROM which will be

available from the Publishers by early

January 1999.

12V

100n

200k

110k

LEFT

ACTIVE

INV INP

VOUT

+IN

OUTSENSE

NOTCH

100p

470p

200k

110k

E+

RIGHT

JP1

E–

LH0038

GAIN1

GAIN2

GAIN3

GAIN4

GUARD

100p

OFFSET

GNDSENSE

330k

BAT85

GAIN

JP1

GAIN

GND

OPEN

100

7 – 8

200

5 – 6

3 – 4

}

400

7 – 8

1 – 2

9 – 10

11 – 12

500

1000

2000

100n

12V

992010 - 12

Figure 3. Circuit diagram of the ECG input amplifier. The circuit employs an LH0038 programmable-gain amplifier.

4 - 1/99 Elektor Electronics EXTRA ——————————————— PC T OPICS

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