Wednesday, 2 October 2013
Make: Visualize Your Heartbeat With This Homemade Pulse Sensor
It s a front end sensor for measuring your pulse rate with an arduino, raspberry pi or any other board with GPIO access.
The principle is simple, illuminate the inside of your thumb with an LED, and measure how much light comes back. It works because there is an artery in your thumb that reflects back some of the light, but as the blood pulses the diameter of the artery increases so it reflects more light.
The Op-Amp circuit detects these changes in light level, amplifies them and passes then as a clean digital signal onto the processor board.
The whole thing can easily be built on vero-board or some other pre-printed generic PCB, although in practice if you were just making it out of curiosity I can't see any reason why it wouldn't work on a breadboard.
It only uses readily available components, although its not clear why they use a quad op-amp and then don't use half the circuit, perhaps it was just the way their PCB was made. Personally I would try a dual op-amp to save space and few pence.
For full details, and a video, go to http://makezine.com/video/visualize-your-heartbeat-with-this-homemade-pulse-sensor/