The plan now is to get the console to a workable state as a keyboard, excluding the track ball, jog wheel, and VFD section. Those are all related to the main board, which will be my next target.
## Preparing to test
I've mounted all three boards (sans main board) in the enclosure again, intending to connect the ribbon cable to a Raspberry Pi and see if I can get keystrokes to register. (No, I won't be using a Raspberry for the final product, but for prototyping it's okay.) For that purpose, here's (one way) how the control panel's 36-pin ribbon cable can be connected to the Raspberry's 40-pin header:
The thing is ... at the time of writing, I don't even have a proper breadboard for this. I only have a tiny 25x14 breadboard that absolutely doesn't have enough room for an additional 36-pin ribbon socket when the majority of it is occupied by an "Iduino GPIO Expansion Board". But, I did have an old FDD cable (34 pins!) lying about that tore up and made work more or less "dead bug style".
## All wired up
Ain't she pretty? (Please say no.) The good news is, I've got the Axial's ribbon cable connected to my Raspberry Pi.
## Good and bad news from the outside world
The good news is, I've been contacted by a possible sponsor willing to provide me with any pcb fabrication I might need! Clearly, I do have a need ... but it may not be very urgent, because of:
The bad news: I would really, really like to run this project on a Teensy 3.5 (large GPIO count, 5V tolerant, good libraries incl. USB HID mode) ... but what with the global chip shortage, I can expect to have one in my hand by 2023Q2 ... maybe.
In the meantime, I've ordered an Arduino Mega 2560 which at least has plenty of (5V tolerant) GPIO ports, but we'll see how much of a fight it will put up when asking it to be a USB HID device.
The bestest news: Before ordering the Mega, I posted a query to the Hackaday Stack, asking if anyone had a spare Teensy 3.5 they would be willing to part with. Turns out, not only did I get a reply in time to cancel my Mega order, the reply was from Paul Stoffregen himself. Thanks, Paul, you truly are an amazing human being!
The slightly bad news: Shipping the Teensy will take "1-3 weeks" (once it's handled and actually sent), and then probably another week or so when the local customs people want their slice of it.
## Key mapping
I've thrown together a small program to repeatedly cycle through all combinations for the G2A, A, B, and C lines, while looking for signals on any of the return lines. With a bit of user input, this allowed me to map each signal combination to a specific key, which I've stored in a CSV file for now. That was easy enough (once I had debugged two crossed ribbon lines and another that had come loose). As it turns out, three or four keys are either dirty or close to being kaput, judging by their responsiveness.
Next up would be translating this to "user input" for the Raspberry Pi itself, and after that I'll see about passing that input on to a USB host (but that's going to have to wait until I have a USB-device-mode-capable microcontroller).
So for now ... I'm waiting on delivery of the Teensy, and in the meanwhile digging more into the main board logic.