I love the electronics videos Collin Cunningham produces for Make: Online. Not only does he describe his projects in an entertaining way, he also scores the trippy music for them.
After checking out a few projects involving IR heart monitors, I decided to have a go at the interface myself. Seen above are the results of my first experimentation with pulse oximetry. Getting the setup up and running satisfactorily required a bit more time and tinkering than I'd expected - especially after reversing a premature mod to my emitter/detector pair. The next version I try will either use a higher output emitter (see Charles Martin's version) or some amplification hardware (as used in Meng Li's sensor).
Mark Frauenfelder is the founder of Boing Boing and the editor-in-chief of MAKE and Cool Tools. Twitter: @frauenfelder. Come and hear Mark speak at the ALA conference in Chicago on July 1.