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Design Project-"Psiological Signal Simulator"
Project Management, System Integration, Electronics, 68HC11
Design Project
Work Ended April 14, 2003
Rajbavan Sivaramalingam
An extensively comprehensive report is available in hard copy.

Abstract:

A "physiological signal simulator" is a testing and teaching device. The following five physiological signals are simulated: ECG, arterial blood pressure wave, pulmonary artery pressure wave, airway pressure signal, and heart sound waveforms or phonocardiograms. The design uses MC68HC11 platform and allows for simultaneous display of up-to five signals in a typical oscilloscope. Also, the system allows the user to adjust frequency, and pressure values. The design is unique because it seeks to trade off low cost, tedious design for high cost alternatives.

Introduction:

Primarily from 1950's physiological parameters were measured and/or monitored using electronic instrumentation to diagnose diseases, and to evaluate and monitor a person's health. Simulator of physiological signals is useful as a teaching aid and as "proof of performance" testing devices. The signals simulated, the hardware and software requirements, the economic factors make each simulator to be unique.

Theory:

Five signals that are important to be monitored in the cardiovascular and related systems are electrocardiogram (ECG), arterial blood pressure, pulmonary artery pressure, airway pressure, and phonocardigram (PCG).



Signals Control Specifications:



Hardware Description:

Stand Alone Physiological Signal Simulator Circuit

Software Description:

The system consisted four main parts:

Information Acquisition: Acquire and properly store user information about the number of graphs, the type of graphs, the type of adjustments and, information regarding navigation.

Display Dispatcher: The algorithm that based on the user requests, properly sends data to the display.

Controls: Frequency, amplitude, and other controls corresponding to signals under consideration.

Robust Interface: Allowing for flexible user navigation, and options.

The hardware platform has already been selected. The selection of HC11 will require us to implement the system using its assembly language.



The user input was received from five simple switches which were polled. For instance, in state two the user information is handled as follows:



Design Assessment:

Here are items we were able to implement:
  • Display one or more graphs
  • Adjust Frequency (but not preciously)
  • Adjust Pressure Values (not preciously)
  • Provide user interface

    However, there were series short comings.
  • High frequency noise was not filtered out properly
  • When 4 or 5 graphs were displayed high flickering occurred
  • Also, all the controls required were not implemented

    Epilogue:

    Although the project had many learning opportunities, it was not a successful useful product and was incomplete. Lack of end-product vision, proper research, proper division of labour and resources contributed to our not so "successful" project. However, we received a B+, because we demonstrated great independence and persistence in tackling problems. We understood the elements such as cost, time, demand, and intangibles that are involved in product design and implementation. We understood the gab between an idea and product, the need for design and documentation before implementation, and the grave importance of properly defining the scope and vision of the end product.

    We conducted a "Postmortem Review", and we drew various lessons from the project. The requirements and the demand for the product should have been assessed more realistically. For instance, consulting the hospital technicians and medical students should have been done. An up-front and detailed literature review using IEEE databases, "The Applied Art and Technology Index", former undertakings, and "expert" consultation should have been done. A more direct, open and immediate consultation with our faculty advisor would have resolved issues that consumed large chunk of time figuring out ourselves. We were good starters, but we were weak finishers and that must change.