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.

Here you can see my “sensor”:

Here is the connection to the DS:

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)

A neat-looking device for DS homebrew development is natrium42’s DSerial. The features include

• 8051 microcontroller running at 24MHz
• Reprogrammable from DS, premade firmwares available
• Free development tools available
• 18 GPIO lines, 2 status LEDs
• UART with RS-232 level converter (can be disabled)
• Full-speed USB 2.0 device (does not support USB host)
• PWM and ADC available
• 2D tilt sensor

I’m hoping to make some cool stuff with it…my first plan is to build a portable heart monitor, that can also tell you how stressed-out you are, based on your ‘coherence’ (essentially you take the FFT of your heart rate over time, and you want most of the energy to fall near to 0.1Hz)