UPDATE: An improved ECG design was posted in August, 2016.
Check out: http://www.swharden.com/wp/2016-08-08-diy-ecg-with-1-op-amp/
I kept working on my homemade ECG machine (I had to change the values of some of the resisters) and it looks like I’m getting some valid signals! By recording the potential using my sound card (microphone hole = a nice analog to digital converter that every PC has) I was able record my ECG with sound recording software, smooth it, and this is what it looks like. Pretty cool huh?
This was based on a circuit I made using a single op-amp (A LM324 from RadioShack $1.49). Basically the op-amp just amplifies micropotential generated by my heart and outputs it in such a way that I can connect it to a standard headphone jack to plug into my microphone hole. The signal is very noisy though. I’m thinking about making the intricate circuit (with 6 op-amps) to produce a better signal-to-noise ratio, but first I’ll try coding my way out of the noise.