Pulse Necklace 15Oct2009
 Hack Notes, Pulse Choker, Oct 15th 2009
 Comparison of Choker Prototypes
The older chokers made from conductive paint are now have crakes in them. We’ll continue seeing how the conductive thread version holds. We’re going to hold off buying more silver paint for now.
 Evaluation of Conductive Thread Choker
The right LED (when viewed as a ‘T’) isn’t lighting up reliably, despite being connected and having resistance values similar to those of the left functional LED.
 Getting Reliable Heartbeat Readings
Eric yields nice consistent readings, but we haven’t been getting much success with other people. We’re visualizing our heartbeats on the oscilloscope. We also checked the resistance across our red dot electrodes. Eric placed his electrodes below his nipples and got a signal of 70 kOhm. I had my electrodes placed above my nipples, my reference electrode at the beginning of the bra strip and my signal electrode at V2 (standard ECG electrode placement). That placement got a 260 kOhm reading. When I moved my reference electrode down towards the bottom on my breast, the reading halved to 120 kOhm. We also moved the signal electrode below the breast too and got good signal. Now we know why chest strips are great: the readings were good and the placement is convenient for clothing purposes – bra (and chest strip for guys?).
We also modified our code, placing the threshold to trigger an LED blink at the average + 2 standard deviations. This gave Eric, Stuart, and me reliable signals. Eric got single blinks consistently, and I got mostly single blinks and double blinks on occasion.
 Future directions
We are making another electronics purchase.