Datasheet

Thursday, 17 July 2003 MiniProject: Design Aspects Colin K McCord
EEE512J2 – Electronic Product Design Page 38 Chapter 8: Conclusions
8.0. CONCLUSIONS
Clearly the heart’s strong pumping action is driven by powerful waves of electrical activity, which are
detected by attaching electrodes to the skin. It is clear that these electrical signals are extremely small and
must be amplified considerably (about 1000 times) to be of any use. Evidently an ECG monitor displays
these electrical signals graphically just like an oscilloscope displays voltage variations; expect that the trace
on an ECG monitor scrolls across the screen. The concept of an ECG is not novel one; the attraction of this
project lay in the challenge to build a simple, compact, operational medical device at a low cost.
It is clear that the electrocardiogram (ECG) is a simple, non-invasive technique for detecting abnormalities
and diagnosing heart defects, merely by noting the presence of irregularities in the PQRST waveform.
Clearly other applications 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.
The CRT display (Cathode Ray Tube) is one of the common display types in use today (TVs, monitors,
oscilloscopes, etc...), clearly this technology is coming to the end of its life as new compact low power
technologies like TFT and LCD are becoming more widely used. The main disadvantage of the CRT
(besides it high power consumption) is the way it draws the image, the spot is moved across the screen at
50 Hz, even at 50 Hz some people will still see the display flickering badly (modern computer monitors have
a refresh rate of over 100Hz), and most people experience problems when an CRT display is within their
peripheral vision, causing headaches, dizziness, and eye strain when exposed for long periods of time. The
use of a TFT or LCD display instead of a CRT display is clearly a better option, as the screen does not
flicker, the reason why it does not flicker is because the screen is split up into pixels, each pixels can
modified independently of each other, hence only the changes made to the display are refreshed.
Undoubtedly it is important for a product designer to first produce a couple of simple concept designs (see
figures 3.3a to 3.3c) before starting detailed design. These design can be completely “of the wall” (not
practical), but aspects of which could have contributed to the design of the finished product. After market
research and the concept design stage, it is time for a designer to make some decisions and come up with a
detailed product design specification that engineers can use to carry out detailed design of the product.
Obviously this product design specification should be flexible, as engineers working on the product may have
thought of a better way of going about a certain problem, new ideas, or certain aspects of the specification
are not practical and have to be changed.
One of the main problems with the design of any product is compliance with international standards, and
because the ECG monitor is designed for medial usage these standards are extremely high. Clearly
international standards are a must, as this ensures the technical operation of the product over varying
conditions and ensures the product is completely safe. Without these standards there would be a lot more
low cost electrical goods on the market, which maybe unsafe, hence the reason why electronic products
without ISO compliance should not be purchased. Allow this does not necessary mean that the product is
unsafe, but with compliance a product is practically guaranteed to operate correctly and safely. The ECG
monitor must fulfil the requirements of the medical device directive 93/42/EEC of the European community in
order to be used as a medial instrument. Note international standards are updated regularly, hence it is
important to keep an eye on them throughout the development of the product.
Powerful software applications like “Microsoft Project” are extremely useful for manning projects. A detailed
plan addressing all aspects of the project from initial brief though to manufacture, sales and distribution was
easily made. The software application automatically calculates development costs by calculating how long
each employee spends of each task and multiplying it by their hourly wage. Gantt charts, PERT charts, and
various forms (e.g. development costs) are easily generated by the system. The total development cost for
the ECG monitor was estimated at £24,646, taking into account only personal wages, never mind overhead
costs (power, telephone, etc…) and prototyping costs.
Clearly commercial ECG monitors are over priced; the main goal of this project is that the cost should be as
low as practically possible, the total manufacturing cost is predicted to be £315 (£450 retail price) and this
figure is being used as guild when selecting hardware components. The predicted retail price of £450 is a
little higher than originally planed (due to compliance with international medial standards), allow the real cost
of the project is likely to be lower (over estimated), clearly it is still much cheaper than existing portable