From the MAKE Flickr pool
Charles is using an Arduino ethernet shield to send the rhythm of his heartbeat over a network in the form of OSC messages. Each beat is detected via a simple sensor comprised of an IR LED and phototransistor -
The idea is that when your heart beats you have a quick rush of blood into tiny blood vessels close to your skin which makes it less transparent. This effect is easiest to observe on your finger tips or earlobe. So the IR emitter and phototransistor are placed next to each other (not much light goes through the side of the emitter!) and I put my finger on top. Light from the IR emitter illuminates my skin and is reflected into the phototransistor.
The phototransistor is connected to the Arduino in a similar way to a potentiometer. One lead is connected to +5V and the other to ground. The +5V lead is also connected to an analogue input on the Arduino. When the phototransistor receives more IR light it becomes more resistive and a lower voltage is detected by the analogue input.
His sensor was built using Meng Li’s instructions & schematic. Looks like a great input option for those interested in experimenting with biofeedback.
In the Maker Shed: