Last week, I bought something I’ve wanted for quite some time: an oscilloscope. I’ve been doing more projects where a scope would be useful, such as audio amplifiers, PWM, and AC-DC rectification. And besides that, oscilloscopes are just plain cool. Of course, a scope by itself isn’t much fun, it needs something to measure. Something like an AC sine-wave, or an audio signal, or maybe… a person’s pulse rate? It’s possible, with the right sensor. Sean Michael Regan shows us how in the latest MAKE Weekend Project. I knew right away that it was perfect for trying out my scope. It was a bit of work, primarily because I modified the circuit, but the finished sensor is a lot of fun, and there is a lot of potential for doing more with it.