v0.7

NeuroBytes v0.7 was a bit of a throwback to v0.4. We took a few of the lessons learned in v0.5 and v0.6--directionality, pogo programming, SMD connectors, etc--but focused on BOM cost by reducing the number of indicators and dramatically shrinking the PCB.

Five v0.7 prototypes midway through soldering, showing the QFN-28 ATtiny88 and single RGB LED.

Five v0.7 prototypes midway through soldering, showing the QFN-28 ATtiny88 and single RGB LED.

This version included four dendrite connections, meaning the inputs tied up eight ATtiny88 I/O lines (since each interconnection includes a signal and a 'type' line to differentiate between inhibitory and excitatory signals). The unpopulated pad shown between the four dendrite outlines is an 8-element 10k resistor network; using these parts for input pulldown saved a ton of space!

NeuroBytes v0.7 also used the VQFN-28 version of the ATtiny88. This package only has 28 pins versus the 32 on the TQFP used in v0.5 and v0.6; the lack of excessive indicators meant the reduced I/O count wasn't an issue. And VQFN devices are tiny--in this case, 4x4 mm versus the 7x7 mm TQFP (or 9x9 mm with leads). These packages also have a large metal pad on the back that must be soldered down, which can be a bit tough to do by hand. We managed to avoid reflowing the prototypes by including a massive plated hole on the back of the boards for hand-soldering the pads.

We also started building out standard accessories, such as this switchable exciter/inhibitor:

Exciter/Inhibitor prototype, later committed to a dedicated PCB.

Exciter/Inhibitor prototype, later committed to a dedicated PCB.

Dedicated breakout boards for accessories--exciter/inhibitors, bump switches, extenders, and the like--mean we can standardize the cables, which makes sense for manufacturing. However, a few days after ordering custom boards for accessories, we decided to move on from the JST SH connector...