I have a prototype of the hardware side of my Nintendo DS-based heart rate monitor. I’m using the awesome DSerial to interface an IR LED & IR phototransistor to the DS.
It works ok, but the signal is not strong enough. Slight movements can make the data unusable. I think I need to work on either amplifying the signal, or increasing the sensitivity of the DSerial. Also I need to rig up some velcro to stick the sensor to your finger, so you don’t have to hold it in place.
And finally, here is a screenshot of the DS’s lower screen, which is just graphing the data coming from the DSerial’s ADC:
Check out this movie of it in action: dserial_heart_monitor.avi (1.5MB)