Datasheet

Thursday, 17 July 2003 MiniProject: Design Aspects Colin K McCord
EEE512J2 – Electronic Product Design Page 39 Chapter 8: Conclusions
commercial ECG monitors as the cheapest was £798 and it only had a printer for ECG output, no visual
display, no PC communications, very basic.
Clearly line balancing is very important, as this ensures that the production line is almost optimal, keeping
production costs to a minimum. There are powerful software applications designed specially for this task,
and there are many good manual methods that managers can use. Evidently a balanced production line for
ECG monitor can be achieved using 4 work stations with a balancing delay of only 9%.
The RS232 transport medium was chosen to transmit the ECG to a PC in real-time, the main reasons why it
was chosen is because it is easy to program, reliable and every PC has at least one RS232 port. The main
disadvantage of RS232 is that it is slow (max speed 115kbps) when compared to other mediums (e.g. USB
12Mbps). Because the ECG monitor is only sampling at 128Hz, the speed of the RS232 port is more than
enough.
Unmistakably the partitioning of work is extremely useful, as even the most complex of task can be split into
a number of small simple tasks. The design of a plane for example is clearly too complex for one person to
fully understand all aspects of design and must be partitioned many times over, until the partitions are small
enough to be manageable tasks. Besides the obvious (simplify design) the partitioning technique has many
advantages, the main one being system flexibility, e.g. modules can be modified without the need to
redesign the entire product. But it is important to note that a well designed non-partitioned design (difficult to
achieve) will likely be cheaper and operate more efficiently, clearly this is not commercially viable as the
product would not be flexible (difficult to change) as all aspects of the product are intertwined and rely on
each other, and difficult to service (repair, upgrade).
It is clear that the ECG monitor should not rely totally on the low-cost of the product to attract customers, the
shape, form, aesthetics, styling, tactile qualities / human interaction surfaces, visual interaction should be
designed carefully. Research shows that most humans buy on impulses (Looks fell of the product) rather
than the technical aspects of the product (with the exception of engineers, who are obsessed with technical
details). Note most electronic engineers would be happy to place the product in a standard square box,
drilling a couple of holes for switches and knobs. Clearly a design engineer should design the packaging, but
their must be a close relationship between the design engineer and the electronic engineer as the PCB
board must fit the case with switches and indicators lining up with holes in the case (no point having a cool
case if the electronic circuit does not fit, or does not offer adequate cooling).
Obviously accuracy, dependability, and precision are an absolute must for the ECG monitor as the device is
to be used for diagnostic, and other medical purposes. Clearly any small fluctuation in the waveform
generated could carry critical diagnostic value. It is obvious that noise is the main design consideration, as
the ECG is extremely small and can easily be masked by noise related fluctuations. The ECG amplifier must
amplify the ECG single (1000 times) and not the noise, hence the need for an expensive “instrumentation
amplifier” with a high CMRR. This explains why the ECG amplifier is the single most expensive module
within the ECG amplifier.
Clearly the designed digital circuitry is low cost (under £20), if the same function was designed using
analogue circuitry the cost and chip count would be extremely high. The design shown in 7.3a includes every
that this required to produce a working prototype, but clearly development is required to comply with
international standards, i.e. RS232 communications must be isolated.
This report clearly demonstrated how to design and plan the innovation of a new medical device, from the
feasibility study through to physical realisation / manufacture of the product. Evidently there is a market for a
low cost ECG solution, which is commercially viable to produce.