deskthority

Starting a separate thread here, since I'm finally getting to sink my teeth into the project.

I'm looking to build up two 3270-layout M122s, one for my desk and one for a project. The second will have a Raspberry Pi built in, as well, and will be basically a complete computer in a keyboard - running mainframe software via the Hercules emulator. As part of this, I'm going to be building up a couple of M122s with QMK. The idea is that they'll act like a regular PC keyboard (though true to the key labeling, which varies a bit from the usual PC layout) normally, but when a TN3270 program like x3270 gains control, it'll automatically switch into as faithful an emulation of a real 3270 keyboard as I can get, via a layer switch in QMK.

I'd originally planned to use a Teensy++ 2.0 for the keyboard controller, and have one built up and programmed and running. The impending demise of the 8-bit AVR controllers has me rethinking that plan. I've got a Teensy 3.5, but it's not directly supported by QMK. I'm starting to look at some of the alternatives, and rapidly running into a bewilderment of riches. What's the current thinking on controller hardware? I'm not looking to do a complete custom PCB, but rather a carrier board that a rebuilt controller like the Teensy or the BlackPill can be soldered to. I need 28 digital I/O lines, minimum, and that's without LEDs or sound or anything else.

Also, anyone have a complete set of 3270 keycaps? I've got one M122 with a 5250 data entry layout, and can repurpose that one if I can get a good set of keycaps for it.

Just ordered 10 BlackPills, whee...since it's natively supported and widely used in the QMK community, according to their Discord.

QMK should be able to interface with the stock controller board just fine as a converter. If you're really wanting to do direct matrix connection I'd recommend just harvesting the FPC connectors from the controller board kinda like this.
There's a few projects floating around for USB replacement boards that could probably be flashed with whatever your custom firmware ends up being.

jsheradin wrote: 02 Jun 2021, 01:26 QMK should be able to interface with the stock controller board just fine as a converter. If you're really wanting to do direct matrix connection I'd recommend just harvesting the FPC connectors from the controller board kinda like this.

Spoiler:

IMG_20201027_184432.jpg

There's a few projects floating around for USB replacement boards that could probably be flashed with whatever your custom firmware ends up being.

Why harvest the connectors? Those Trio-Mate connectors are still available. When I built a test board for diagnosing matrix problems with an M122 recently, I used Mouser part numbers 571-7-520315-0 (20-way) and 571-5-520315-8 (8-way).

Sheepless wrote: 02 Jun 2021, 02:05 Why harvest the connectors? Those Trio-Mate connectors are still available. When I built a test board for diagnosing matrix problems with an M122 recently, I used Mouser part numbers 571-7-520315-0 (20-way) and 571-5-520315-8 (8-way).

The new Mouser parts are actually what's shown in my picture, one of them is just trimmed short. I just figured if the controller board is getting replaced anyways then the connectors might as well be put to use and keep cost down a bit in the process.

I guess if the controllers are going to be used for repairing a different board or something then sure, keep them in one piece.

I bought 10 each of the connectors from Mouser. (After fighting and losing to Digi-Key's online ordering system...) And I'm replacing the controller to get the power draw down, as well as save room in the case for the Raspberry Pi.