v0.4 requires a bit of extra consideration; in addition to scaling manufacturing by more than an order of magnitude, this generation was current for more than a year and was the basis for Zach and Joe's collaboration. During its lifespan, v0.4 took us to The Hackaday Prize 2015 Best Product Finals and helped NeuroTinker, LLC land a Phase I SBIR grant from the National Science Foundation. This overview consolidates a lot of scattered information from Zach's Hackaday Projects site (1, 2, 3, 4, 5, 6, 7) along with numerous other sources.
The primary goal of NeuroBytes v0.4 (called "Neuron" at the time) was to prove out the core concept of the product at pilot scale quantities. We wanted this generation to be low-cost, physically small, flexible, and durable enough to start getting in front of potential users. Zach made a brief overview video in late 2014 that dives into more details:
NeuroBytes v0.4 was the first generation based around a discrete microcontroller rather than a more expensive (but easier to use) Arduino board. We selected the ATtiny44A for a few reasons: low cost, I/O capability, and--most importantly--AVRDUDE, the friendly command-line utility that gives the ATtiny series an entirely open-source development toolchain.
We also decided that the v0.2 indication method--an RGB LED--was the way to go, as it closely mirrored Andrew's original software design and clearly showed when neurons were excited, inhibited, firing, or at rest. Buying the cheapest LEDs on Digi-Key probably wasn't the best choice as the 605nm "red" ended up being more of an orange (my fault), but they worked well enough for prototyping purposes.
NeuroBytes v0.4 needed to be modular; we wanted to put the platform in front of students and educators alike. As such, the connector design was crucial to the success of the prototype. We ended up with insertion-mounted TE Connectivity 2mm headers which worked well enough for this generation:
This project was Zach's first foray into real circuit design. He picked his way through a few KiCad tutorials and ended up with a simple schematic and layout:
The previous physical NeuroBytes prototype iterations only existed on a breadboard and interacted with the real world through a couple of pushbutton switches. The new boards eventually spawned a range of accessory modules that improved usability, some of which are shown here.
Pilot Scale Production
In a somewhat risky move, Zach skipped prototyping the circuit design and jumped right into pilot-scale production; in this case, that meant ordering four panels of 32 boards each. The boards were solder pasted and populated by hand, reflow soldered in a modified toaster oven, then hand soldered for the seven connectors.
If you want to learn a bit more about the pilot scale process we followed, Zach gave a talk at The Hackaday Superconference 2015 highlighting a few details: