Scott Harden’s DIY electrocardiogram (ECG) uses a LED shining light through his finger into a photo transistor, with the resulting signal amplified with a LM324 quad op amp.
The goal of this project is to generate an extremely cheap, functional ECG machine made from common parts, most of which can be found around your house. This do-it-yourself (DIY) ECG project is different than many others on the internet in that it greatly simplifies the circuitry by eliminating noise reduction components, accomplishing this via software-based data post-processing. Additionally, this writeup is intended for those without any computer, electrical, or biomedical experience, and should be far less convoluted than the suspiciously-cryptic write-ups currently available online. In short, I want to give everybody the power to visualize and analyze their own heartbeat!
In the first YouTube video above, Scott shows how to build the detector. The second one he shows how to plug the detector into a computer sound card.