Finally got to the displays. I had a bit of trouble with them, but was able to resolve all the issues in the span of a couple of hours.

The biggest problem I encountered was that writing to the displays too quickly was causing collisions where the subsequent write was ignored. I wasn't sure why this was happening initially since it was happening when I ran a test script, but not when I did it manually. Anyway, I added a delay and it worked fine. I got the timer down to 25ms, but thought I'd try adding a linefeed when the Arduino was working. This got the overall time down to 4ms, so I'm sticking with that solution.

I had a few other minor changes to make, but now the 7-segment displays and LED bargraphs are working as expected! I'm really excited since that's a major milestone. I still have to review the PCB diagram before ordering, but we're really getting close to full prototype status!