Week 10: Nicoletta & Sean

Sean

The last 2 weeks have been laser focused on finalizing EmotiBit Beta boards to send out for manufacturing. With Beta partners ranging from artists like Nicoletta to professors at MIT and folks working in the EdTech space, we could not be more excited to get EmotiBit into more people’s hands and see what folks do with the physiological and emotional signals from their body! ​

For EmotiBit Beta we’ve carefully designed and engineered a number of new features and improvements starting with making the boards pin compatible with the entire Adafruit Feather line of boards to allow WiFi, Bluetooth, LoRa, 4G or any number of other channels to wirelessly communicate your emotions to a friend! We also added LEDs to give the wearer ready indication for the recording, connectivity and battery status when using EmotiBit. ​

In addition to improved interfacing, we also dialed in a number of our sensor circuits to get truly research-grade signal quality. We added the Melexis MLX90632 medical-grade temperature sensing thermopile to measure the tiny fluctuations in body temperature that accompany emotional reactions. Although it’s the single most expensive part on the entire board (nearly $15 each), we decided it was worth the extra expense to see what Nicoletta and our other Beta partners could do with the absolute best quality signal we could deliver.

We also worked super hard to create the most sensitive EDA circuit that we know of. Targeting the ability to resolve skin resistance changes as small as 1kOhm over the extremely wide range of naturally occurring skin resistance (10kOhm to 30MOhm) required weeks of modeling and testing our EDA circuitry to get it just right. The culmination of that work is the small (less than 1cm) strip of board we affectionately call EDA village, with cute little opamp houses surrounded by capacitor and resistor parked cars, we are super stoked about the resulting signal quality!

With a board that’s only slightly bigger than your thumb and hosting nearly 80 components, we also devoted substantial engineering effort to follow best practice mixed analog and digital signal design guidelines. Separating analog and digital power planes and adding an inductor and over a dozen capacitors (including one that’s a whopping 1.2 x 0.6 millimeters in size), we expect noise on our Beta production boards to be in the sub-microvolt range.

Last but not least, we learned from a year of working with our Alpha partners that SD cards are wild beasts that must be tamed! In addition to write delays and large surges of current that need to be carefully handled by the analog/digital power conditioning, they also can draw nearly 2.5 milliamps of quiescent current. That may not sound like a lot, but when you have a wearable form factor with only 400mAh of battery, 2.5 mA would kill your battery in about 6 days. To make sure EmotiBit’s battery isn’t dead every time Nicoletta goes to use it, we added an updated hibernate circuit that entirely shuts off the EmotiBit power draw and extends the hibernation battery life up to 4 months. 

All in all, we couldn’t be more excited to bring EmotiBit Beta into the world and into the hands (or anywhere else on the body) of Nicoletta and our other Beta partners!

​Boards go out for manufacturing this week! 

Happy Thanksgiving everybody!