Datasheet

Thursday, 17 July 2003 MiniProject: Design Aspects Colin K McCord
EEE512J2 – Electronic Product Design Page 1 Chapter 1: Introduction
1.0 INTRODUCTION
The heart’s strong pumping action is driven by powerful waves of electrical activity in which the muscle fibres
contract and relax in an orchestrated sequence. These waves cause weak currents to flow in the body,
changing the relative electric potential between different points on the skin. An electrocardiogram is a
biophysical instrumentation device that is used to view/record the electrical activity of the heart for various
diagnostic purposes.
The electrocardiogram (or ECG) has been used extensively in medicine sine its invention in the early 1900’s,
and has since proven to be invaluable in various diagnostic applications, such as the detection of irregular
heartbeat patterns (i.e. fibrillation or arrhythmia), heart murmurs (or other abnormal heart sounds),
tissue/structural damage (such as valve malfunction) and coronary artery blockage. Other applications of the
ECG are very effective in areas of sports medicine, or sports therapy, in tracking the heartbeat through
various levels of physical activity to assist the patient in attaining a desired, optimum heart rate.
Figure 1.0a. ECG used to diagnostic abnormal heart
Figure 1.0b. ECG for sports therapy
Therefore, while the concept of an ECG is not a novel one, the attraction of this project lay in the challenge
to build a simple, compact, operational medical device at a low cost. The basic design theory is as follows: -
• The electrical activity of the heart is detected using electrodes placed on the surface of the chest
cavity. These electrodes act as bio-transducers to convert the signal from its existing form in the
body (ionic) into electrical current in the wires.
• The generated signal is put through an amplifier to allow for observations, measurements, and
recordings to be made. This stage is extremely important, as the cardiac signal is very small, i.e. on
the order of mili-volts, thus a large amplification is necessary for any use to be made of the signal.
• The amplified signal is then sent to the PIC for Analogue-to-Digital conversion, signal manipulation,
calculation of beats per minute (displayed using 3, 7-segment LED displays), data logging (RS232
communications) and analogue signal output (DAC) for a visual display of the ECG. Note that an
oscilloscope can be used to provide a visual output.
This report will demonstrate how to design and plan the innovation of a new medical device, from the
feasibility study through to physical realisation / manufacture of the product.