Pulse oximeter is a device that mainly measures arterial blood oxygen saturation. As side measurement a pulse is also measured. Probably you’ve seen a small device that is put on a finger tip where one side of clip has a light source while another has a receiver. Depending on how much light is absorbed by hemoglobin parameter is calculated.
This device is based on 68HC908AB32 microcontroller and is capable to measure pretty much same parameters as ones you’ve seen in clinics. Well we are not talking about how reliable this is, but anyway project is handy for personal experiments. And for sure at least it displays pulse correctly. Along with other features it has quite big (192×64) graphical LCD and four buttons for navigation. Project description is in Polish so be sure to use translator.