Yoga Breathalyzer


Last weekend was the Silicon Chef Women’s Hardware Hackathon at Stripe in SF. The event was hugely successful, with over 200 ladies defying the stereotypical Dave-to-girl ratio of electronics hobbyists. It was just like a gender-neutral hackathon, except that they had smaller-sized tshirts to hand out (yay!), and all the diet sodas were gone in about 2 seconds.
Our team of five wanted to make a biofeedback relaxation game. The project took a very, very winding road to a destination far from where we thought we were headed, which I must admit was half the fun. In the process, we looked at several different measures of biological state and anxiety level: galvanic skin response (GSR), heart rate, and peripheral temperature, as well as a few others that we didn’t have the appropriate hardware to implement (eye tracking, respiration rate).
We made two different GSR meters, neither of which worked very well. One was based on aluminum foil, while for the other we got to cut some custom PCBs to use as electrodes instead of using the recommended pennies. (Tip: it’s really hard to solder anything to a penny.) Regardless, neither was very effective. Oh, they measured something, but it had no apparent relation to the user’s mental state. Regardless, they were fun to make — learning to design/cut custom PCBs with an Othermill was really, really cool.
We also played with a pulse sensor that measures reflected green LED light to quantify heart rate. It turns out that the newer versions of this sensor work pretty well, but the older one we had wasn’t very accurate, so we scrapped the pulse-monitoring idea too. 
We put some effort into getting data out of the Arduino and into a Google spreadsheet, with the idea of recording data daily to monitor changes in your biological state over time. This turned out to be weirdly hard; there’s lots of room for improvement in tutorials for this kind of thing. 
In the end, we used a temperature sensor to monitor the temperature of the user’s palm, under the theory that stress lowers peripheral temperature, and combined this with a headset-mounted wind sensor to visualize the user’s breath. It actually turned out that the breath visualization aspect was my personal favorite part of the project, so I wrote up an Instructable on it. 
We were proclaimed the Most Relaxing hack, but more important, we all gained some new skills and spent an amazing weekend hacking with super smart and delightful ladies and fabulous mentors.