Update: The DIY ECG project has had several iterations. The latest one can be viewed here: https://www.swharden.com/wp/2019-03-15-sound-card-ecg-with-ad8232/
Warning: This post is several years old and the author has marked it as poor quality (compared to more recent posts). It has been left intact for historical reasons, but but its content (and code) may be inaccurate or poorly written.
I followed-through on yesterday’s post and actually tried to build an ECG machine. I had a very small amount of time to work on it, so instead of building the fancy circuit (with 6 band-pass filtered op-amps and diodes posted in the previous entry) I built the most crude circuit that would theoretically work.
I used just one of the 4 available op-amps from a LM324. I built this, hooked it up to my sound card, and made electrodes by soldering wires to pennies. After a good lick, I attached the pennies to my chest with tape and tried recording. Every time the pennies made contact with my skin, I would see noise on the trace, but I couldn’t seem to isolate a strong heartbeat signal. This is what I saw and the circuit I build to see it:
Perhaps this project will be working soon. Many techno-savvy people have made these DIY ECG machines, but not many describe how to interpret the data. Since I’m planning on building it, testing it, recording ECG data, and processing/analyzing it, I’ll may have something unique on the internet.