It's time for me to Ki(Cad)

A project log for RAIN Mark II Supercomputer Trainer

High-Performance Computing for Everyone

jason.gullicksonjason.gullickson 04/09/2018 at 16:380 Comments

I’ve been putting-off learning to use an EDA for quite awhile. You see, I am old, and I learned how to read and draw schematics when I was young, so I learned how to do it on paper, and it’s very hard to give-up doing something you can do fast and well for something that is slow, frustrating and you suck at.

In the previous RAIN PSC design, I could get away with using the plentiful GPIO pins available through the PINE A64‘s 40-pin connector to drive the front-panel LED’s and switches.  However, adopting the Clusterboard demanded a different approach and I settled on developing an i2c-based interface. This has worked well on the breadboard, but it requires building an interface board for each node and fabricating something like that out of perfboard (or some other “homebrew” technique) repeatedly is not very practical.

8 of these are probably not going to fit…

Regardless, I thought I could at least cobble-together a prototype of the driver board for a single node so I could at least pack everything inside the case for awhile. A couple of weeks have passed as I’ve tried various options and I’ve come to accept that designing a custom board is the only way to go, and the best way to go about that is getting my design into an EDA.

I’ve put this off for a long time because I’ve made several attempts at learning several EDA’s and it’s always been frustrating. There’s a lot of up-side to learning to use these tools, but paper and pencil is so fast and so natural for me that it’s really had to give that up. Nonetheless, if I’m going to get boards made from my design the options are to either learn this or have someone else do it, and doing yourself makes you smarter so that’s the way I decided to go.

2018-04-07 18.51.07
First attempt (schematic is OK, layout on the other hand…)

I could have learned a number of different packages but I choose KiCad because it’s open-source and one of the goals for RAIN is to be a completely open-source computer. There’s a number of other open-source EDA’s as well, but I got a lot of recommendations to use KiCad and even though it’s considered more difficult to learn, I’ve been told it’s worth it. I also knew that KiCad ran fairly well on my A64-based laptop, and this would allow me to design RAIN’s hardware on the PSC itself.

I started with Getting Started in KiCad (seems like a logical place to start, right?) and slowly made my way through the tutorial, stopping whenever I became the least bit tired or frustrated. I’ve found this to be a good way to learn something I’m not looking forward to learning, because these forced stops cultivate some excitement and curiosity about returning to the task.

2018-04-08 10.16.46
Second attempt, much closer

I was able to maintain this discipline over the course of a weekend and while I wasn’t able to finish the design, I made a lot of progress and learned a lot more than I expected about the tool. Based on what I’ve learned, I feel pretty confident that I will be able to design this board successfully, and continue to use an EDA for all of my future electronics projects.

2018-04-08 10.10.57
Test-fit confirms the form-factor, and also illuminates some design problems

There’s still  work to do before I finalize the design and send it out to have a prototype board made, but what remains is squarely within my comfort zone.

I need to determine whether or not the i2c pins on the Clusterboard need to be pulled-up to 3.3v like they do on the A64 (which would be a drag because the Clusterboard’s pins don’t supply 3.3v) and I need to sort-out some software problems on the SOPINE module just to confirm that the driver circuit will work the same as it did when I had it connected to the A64 for testing earlier. Once these two things are sorted I can finalize the design of the board and order a copy.

With any luck it will work and I’ll be able to pack everything back in the case and focus on the software side of things until I scrape-up enough cash to order more panel drivers and populate the rest of the slots on the Clusterboard.