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Live ECG front end

EECE 2150 · Circuits and Signals

Final lab

An analog front end that picks up a real electrocardiogram from electrodes on a person, cleans it up and digitises it. Instrumentation-style gain in stages, a 0.54 Hz high-pass to remove drift, a 159 Hz low-pass chosen on the scope so the QRS spike survives, then an NI USB-6001 into MATLAB.

Tools: Op-amps · RC filters · oscilloscope · NI USB-6001 · MATLAB

More info

Design

Gain: added in stages and pushed as high as the supply allowed without clipping the R peaks.
High-pass, 0.54 Hz: 200 kΩ and 1.5 µF, to strip electrode drift and baseline wander without touching the heartbeat.
Low-pass, 159 Hz: 10 kΩ and 0.1 µF. Tested 10 Hz (too smooth, the sharp QRS peak was rounded off and shrank) and 1000 Hz (peak intact but far too much interference) on the oscilloscope before settling in between.
Noise: twisted the electrode leads together to cut pickup.
Digitising: NI USB-6001 into MATLAB, plotted in volts and seconds, then rescaled by the analog gain to show the actual voltage at the electrodes.

Result

A clean, readable ECG trace with the QRS complex preserved, recorded from a live person and plotted in MATLAB. Photos of the breadboard, the oscilloscope captures at each cutoff and the final plots are in the lab report.

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