The absolute irony of my absolute failure to put in the time to figure out the unique coding situation to resolve the hot-swapability of this keyboard, and the ridiculous amount of time that has passed since procrastinating on finding a solution to the problem, has left me with an unexpected hardware development...
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In the time that has passed, 20 pin "magsafe style" USB C connectors have been developed, and are now being mass produced. These feature a very dense 20 pin magnetic connector... Honestly... I could essentially "brute force" this
entire keyboard, strictly in hardware, if I were to purchase one of these and wire it up to the matrix, LED driver, and power. I might still need the port expander, but it would interestingly enough, end up situated in the
main keyboard, and not in the number pad. There would be no risk of hot-swap lockup of the firmware, because the I2C would always remain connected to the port expander. Only the matrix, which is normally open anyway, would ever be disconnected, and the power and LED driver lines are non significant. The power just is or is not connected to the numberpad, and the LED driver output is strictly a passive output. It has no feedback at all. This, while a less elegant a solution, does still suit my style of building well, in that I am, and always have been, a hardware type, not a software type. I may be forced to redo the trim featuring the magnets and magsafe style connector, if I'm unable to pop the old ones out. They were epoxied into place, and may never want to actually come out. I will most definitely be slightly irritated, if I have to redo those parts, as the oak I used was very annoying to work with. We'll see...
If I undo my recent alteration, and Switch the LED control back to PWM on Pin D12, and I eliminate I2C all together, I can reclaim pins D5 and D6, and if I eliminate D24 as a numberpad sense wire, that gives me three unused pins that I can assign as new rows R8, R9, and R10 in the matrix. If I feed Columns C1-C12, and the three new rows, R8-R10, that takes 12+3 pins (15), to do a 3x12 matrix, which would cover the entire 6x6 numberpad (I'd do 2x6 groups of keys as 1 row, and 12 columns, electrically). I'd need two pins for power, plus the LED PWM, adding three more used pins to the total count. That leaves 18 pins used, with 2 unused. If I make the + and - power the same pins as the standard + and - USB connections used on that connector, then even if a USB cable is inadvertently attached to the numberpad, it will actually do nothing (it would actually power the LED driver, but the PWM signal would be off). With no communication, the USB would not negotiate fast charging modes, and thus not increase power above standard USB voltages, so again, the numberpad should be safe. For simplicity, I think the numberpad should mate to a USB cable's mag connector, since it'll be almost entirely passive, and thus have the least risk involved. That, at least, mitigates any risk of damage due to error, for using any manner of standard connector. I do belive I did a similar thing with the old MagSafe connector I used previously, where the main keyboard had the cable connector, and the numberpad had the device connector. As for finding what pins are default USB power (5 volts) on the new style 20-pin magnetic USB-C connector... Well, I'll just have to measure. Finding ground is easy. I just check continuity to the shield. It's also almost certainly gonna be one of the big corner pins... Bigger pins are typically used for power delivery. After I find ground, I just measure the other pins to find 5 volts. Simple!
I think I'm gonna order a few of these from China... They'll probably take a good month to show up. I legit wanted to pick one up for my phone. I do not know yet if I even have room to mount these, nor do I know how much larger they are than the 5 pin connectors (they are definitely larger). I want to search tomorrow to see if I can find the connectors standalone, but I suspect I won't. I'll likely be forced to disassemble a USB-C adapter, extract the connector, and solder some 18 wires to 20 of the pins. Should be fun!
I really should just plan on making a new pair of trim pieces. Like I said, I'll have probably a month to wait for the parts to show up off the slow boat.
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