Embedded Microcomputer Systems
Final Exam – Spring 2003
Open book, closed notes. You may have a single page that you have made up summarizing information
contained in your textbook. Answer on these pages only, using the back of the page if necessary. Show
all of your calculations (timing derivations, circuit values, etc.); don’t make me guess how you arrived at
your answer. Read the entire exam before proceeding.
You are to design an “ECG arrhythmia detector” as illustrated below:
ECG
arrhythmia
detector
Silence button
Alarm output
ECG analog input
ECG input: This is a very low-level analog signal in the range +/-1.5 mV. In general, it consists of a
series of “QRS complex” patterns that repeat at the heart rate, as illustrated below (this is not real data):
Filtered ECG Data
-1
-0.5
0
0.5
1
1.5
1000 2000 3000 4000 5000 6000 7000 8000 9000
time (ms)
R-waves
p
remature bea
t
R-R interval
QRS
The R-wave is the prominent sharp positive spike in the middle of the QRS. Detect the R-wave by:
a. using threshold detection at 0.5 mV, and
b. confirming that the width of the wave at the 0.5 mV level is between 10 and 40 ms (either
narrower or wider would mean it is some other kind of wave).
An R-wave that occurs at least 150 ms sooner than expected would indicate a “premature beat”. More
specifically, if an interval between two consecutive R-waves (R-R interval) is found to be at least 150 ms
less than the average of the three previous R-R intervals, the early R-wave is considered premature.
You are to design the hardware and software of an arrhythmia detector that detects premature beats. The
detector should be built around the 6812 microcontroller, plus additional electronics as necessary. The
algorithm you should use for the detection is:
1. Detect the next R-wave using criteria a. and b. above.
2. Compare the R-R interval with the average of the previous three.
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