HeartSavers:
The Final Stretch
TEAM 5
CHRIS HOFFMAN
RYAN KELLOGG
MIKE ZIZZA
APRIL 11, 2007
http://www.ece.cmu.edu/~ece549/spring07/team5/
Status Update
 Project Concept:

Wearable heart monitor: Electrodes in shirt, capture/process signal, send data
wirelessly to smart phone
 Status update: Implementation


Have working hardware
FIFO Buffer implemented, tested on Robostix for storing ADC values



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Eases real-time pressure for polling Robostix
Enables variable length processing time on Gumstix
Gumstix can interact with Robostix FIFO
Progress on ECG circuit: Can see a heart beat, but it’s super noisy
 Status update: Testing and Experimentation
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Performance comparison of different QRS complex detection algorithms
Whether QRS algorithm throughput changes with heart rate
Length of time to do ADC conversion
How long takes to transfer full buffer on Robostix to Gumstix
Experiment Plan #1
 Compare QRS detection algorithms


Overall performance (speed, accuracy)
Does performance depend on frequency of QRS complexes (heart rate)?
 Metrics:
 Run Time (sec)
 Accuracy (%)
 Why they matter:

Helps us decide which is best for our project
 How we measure


Script (in C) to run each algorithm 100 times and record performance
values in a file
Compute statistics in MATLAB
Initial Data #1
WQRS vs. SQRS (Execution time)
Does algorithm performance change with heart rate?
0.8
1
SQRS
WQRS
Execution time (sec)
0.6
0.5
0.4
0.3
0.2
0.1
0
0.9
Execution time (normalized sec.)
Relative frequency of QRS Complexes
0.7
0.8
0.7
0.6
0.5
0.4
QRS Complex frequency
SQRS Execution time (Normalized)
WQRS Execution time (Normalized)
0.3
1
2
3
4
5
6
7
Data Set #
8
9
10
This graph compares execution
time for competing QRS
detection algorithms – WQRS
is faster for all data sets tried.
0.2
0
2
4
6
8
Data Set #
QRS detection algorithm
performance depends only on
number of sample points and
not on heart rate.
10
Experiment #2
 Determine sampling parameters on Robostix (ADC
conversion time, transfer rate to Gumstix)
 Metrics


Time (sec)
Data rate (KB/s)
 Why they’re important
 Want to know how many ADC samples we can do


Can we sample fast enough?
How much processing time is left on Robostix?
 How we will measure
 Toggle IO pins and view ADC conversion time on scope
 Take full FIFO (~ 3K), send across I2C, get timestamp on Gumstix at
finish
Initial Data #2
 Set polling frequency to 244 Hz
 Can only send 16 points (ADCs) in one packet
 15 transfers just to get a second’s worth of data
 488 bytes to transfer for one second (244 samples/sec * 2
bytes per sample)
 Results
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
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Time for one ADC conversion: 115 us
Transfer rate to Gumstix: 5.7 KB/s
Time to send one packet 0.1 sec
Looking Forward
 What have learned so far?
 Don’t underestimate the weirdness of analog
 Quirky timing function on Gumstix
 Quirky I2C on Robostix
 Next steps:
 Make ECG algorithms run in streaming fashion
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Run algorithm as daemon, communicate through sockets or pipes
Make the circuit work as expected
Make GUI on phone to display ECG information
Don’t give up on non-stick electrodes
Questions?