Core16: Interactive Core Memory Made Smaller

Here we are. A proper test fixture PCB for reliable testing!

Should have started with a PCB instead of this ugly step on the left.

A close up of the core test area:

And now the Core16 kits are live on www.Core64.io along with the newly inspired SAO OLED kits.

This is the test fixture I had in mind when I started this project:

It mostly works... I made all the interconnections with individual wires. Gross. The next iteration will be a proper PCBA with pogo pin receptacles, and nice reliable traces running from the DUT to the Core Test Matrix. The biggest challenge is the extra resistance in the wires to the Core Test Matrix, making that part of the system unreliable. Everything else works great. I'm very happy with the mechanical moving bits:

Here's some of that nasty wiring:

Did I mention wire harnesses are a time suck?

A lot of my learning and inspiration came from these guys: https://fixturfab.com/

This video highlights the challenges in designing these things... 

...and justifies why it's worth paying them for the service!

Nonetheless, my fixture did help me get through testing all the boards, so now I can move on to kitting everything for the workshop!

Oh, and finish the firmware...

Workshops for Supercon 2023 were announced today and this project is one of them!

Here's a preview of what is in the kit:

Frames are in production to:

One hour and 20 minutes per frame set... But I'm very happy with the result which is easy to print (no supports) and snaps together in a very satisfying way. There are lanyard loop attachment points at the top corners, and from the front, the frame is minimal.

The backside of the frame holds the battery pack and a pair of stylii.

And it stands up on it's own too:

Suitable as a desk clock!

Every project needs a display, buttons, and a command line! Here's the display solution I've come to appreciate:

I've been kicking this idea around for awhile and now it's a reality! These will be available on Tindie in November '23 as a DIY kit. Features and included components:

• PCB
• OLED 128x64 Display 0.96" with 0.1" 4-pin header I2C
• Supporting stand-offs to secure OLED screen
• Solder jumpers to choose polarity to ensure compatibility with the common I2C OLED displays
• SAO plug (bottom)
• SAO socket (top) to extend to more SAO stuff
• QWIIC Socket

Naturally, all of my recent Interactive Core Memory kits are compatible with this and make use of it, if it is connected.

Here's the "functional" test fixture currently being used for production testing:

This falls short of the bar I set initially. But the "real" test fixture still needs some electrical debugging. Something about the core sense signal is be thrown off, and I haven't been able to figure that out yet. But I will get it solved soon! I've diverted to a frame to hold the completed Core16 kit. Look for that in the next project log update.

The Core16 prototypes are alive and well! Everything is working correctly. Even so, a few tweaks and silk screen corrections were in order before releasing a larger batch for a pre-production build. While the boards are being fabricated, I'm working on creating a robust test fixture to streamline testing. For the other Core64 kits, I've been using this contraption I slapped together. Reliable isn't a great word to use when describing it.

Alas, design and assembly time was short.

This time, I kick started the Core16 test fixture by ordering one of these kits from Amazon:

I know I'm in for some assembly adventure, but it should save some time and provide a good base to work with. This might be my first and last DIY fixture. I've learned a lot from the guys at https://fixturfab.com/ through this video. Still, I'm gonna give the scrappy method a chance and creatively consume some junk drawer inventory. And it's all brought together with some 3D printing, of course. But the results are encouraging so far.

That's the moving plate. Seems good enough to move forward with. Now, on to the probe plate with the VERY IMPORTANT integrated power switch! See video linked above if you want to understand the nuances of test fixture design and why a switch is important.

The prototypes are here!

These are 4 of the 5 that were assembled with the JLCPCB service. I had to add the LEDs and four hall sensors since those weren't available with their service. And that is the fifth one show here:

All the LED and I2C circuitry works at this point. Whew!

And that's what it looks like when 16 bits of core memory are woven in place over the LEDs. As expected, it went much faster than 64 bits. I have a design for the screen protector (a must!) but I plan to leave the LEDs exposed without a diffuser layer. Because each pixel is already in its own little well, they look pretty good as is. The well also provide a place for the Core Memory to sit just below the surface of the PCB so they are slightly protected.

Now I'm working on the firmware, adapting it from 64 bits/pixels down to 16. Even though it's not all complete, it already looks eye catching with the RGB LEDs. 

Finally hit the order button. I went with the quickest possible turn-arounds at JLCPCB, which means a bland green PCB. Makes a fine first prototype that is bound to get hacked up as I discover mistakes and make tweeks. It's already in production. And my Digi-Key order is in as well for the components I need to manually add to the prototypes (LEDs, Hall Sensors, battery pack). Here's the confirmation render for part placements that I received. 

Looks good!

Next step is a simple 3D-printable battery case holder so it'll snap on to the back of the board.

I'm very close to prototype release! I need to do some final schematic Ref. Des. # checks this weekend and it should be good to go with a very high confidence of the prototypes working. I'm trying to check and avoid all the mistakes I've ever made before... I know it still won't be perfect but it will close!

I'll need to assemble the LEDs myself, and the core matrix of course. But I expect assembly is going to be lighting quick compared to Core64. The reduced component count makes a lot of things easier.

Component availability looks good for everything. Knock on wood. Digi-Key should expect to hear from me Sunday!