Maker Scott Harden built a ultra-low-cost ECG machine using the sound card on his PC, some free digital audio processing software, a simple circuit, and a few pennies.

Although several DIY ECG guides exist on the internet, this one focuses on minimizing the part count and cost by performing noise reduction (normally handled by complicated analog circuitry) digitally with your computer. The device hooks up to your chest (using pennies as electrodes) and outputs to the microphone jack of your computer sound card so it can be recorded with free audio software. In addition to a description of how to build and use the DIY ECG, this guide also provides the code needed to perform complicated long-term heart rate and heart rate variability analysis to assess neurological control over cardiac function!