Close

v06 prototypes (partially) working!

A project log for NeuroBytes

Build your own nervous system!

zakqwyzakqwy 12/19/2015 at 17:055 Comments

I'm still waiting on a few parts (namely 0402 dropping resistors for the LEDs), but I got one v06 prototype partially assembled last night--and I can talk to the ATtiny88, so I must have done something right with the design!

You may have noticed the six pads on the back of the board design--I wanted to try pogo-style programming, since that's what we'll use when we ramp production up a bit. I deliberately made the pad locations symmetrical along the long axis of the board, intending to use one of the six prototypes as a base for programming (along with some hastily soldered together FR-4 as an alignment rig):

[note: someone at the #Hackaday SuperConference 2015 gave me a few googly eyes that made their way onto my USBtinyISP. Who was that? Thanks!]

The note already tells you something is wrong; during handling I managed to snap off one of the pogo pins. Turns out 1.5mm diameter pads break pretty easily. It's the MISO pin, so I re-purposed the ground plane and added a "splint":

Hilarious but ultimately ineffective--soon after taking this picture I snapped another pin off. Lesson learned--use insertion-mount pogo pins and take the time to make a custom carrier board! In any case, I decided to mount the pins directly to the FR-4; I had to tweak the alignment of a few to get a reliable connection, but this setup worked. I made sure to give each pin a generous copper pad so it wouldn't break off as easily:

I also scavenged a NeuroTinker logo off the scrapped board. The solder mask pullback + ENIG copper logo turned out pretty well, so I figured it was worth highlighting.

Oh yeah, and I didn't remember to implement one of the important lessons I learned when I put together v04: 4-pad SMD LEDs are a PITA to hand-solder and including a bit of extra pad goes a long way. The red/blue dendrite LEDs check out with the continuity tester, but we'll see if they actually work...

Discussions

Amutha Bharathi wrote 12/21/2015 at 22:51 point

Errr.. I think the googly eyes have to be mine . Welcome :D

  Are you sure? yes | no

zakqwy wrote 12/21/2015 at 15:25 point

Membrane potential LED test (100% brightness, which overloaded my camera a bit):

http://imgur.com/bM2vaHl

  Are you sure? yes | no

jonathanfdillon wrote 12/20/2015 at 23:15 point

If you haven't already seen it the sparkfun production and test board tutorial is great.

They use PCB for all the layers to build a jig.

Files for the first example are available in eagle for you to look over

https://www.sparkfun.com/tutorials/138

  Are you sure? yes | no

zakqwy wrote 12/21/2015 at 15:16 point

great article--thanks! I think Adafruit did a writeup on test boards that I read at some point, but I hadn't seen this one before. I'll definitely plan to roll some of these concepts into the production design.

  Are you sure? yes | no

jonathanfdillon wrote 12/21/2015 at 21:36 point

The 2nd board down should prevent pogo pin snapping. 

Also checkout the tagconnect as its an off the shelf solution. I saw it at ARM TechCon and I'm going to put it on a future board http://www.tag-connect.com/

  Are you sure? yes | no