Rolling my own keyboard

[Dan Linder]

On Sun, Sep 17, 2017 at 10:34 PM, <andrew....@gmail.com> wrote:

A TMK fork with an expanded feature set.

https://github.com/qmk/qmk_firmware

On Sunday, September 17, 2017 at 7:49:18 PM UTC-5, Kevin Fusselman wrote:

QMK?

On Sun, Sep 17, 2017 at 7:14 PM <andrew....@gmail.com> wrote:

A keypad for a steampunk-themed desktop set for my wife, writing a customized QMK firmware for it.

Andrew,

I've got a couple questions for you and/or the greater community on this subject. :)

First, thanks for the link - I hadn't seen either of those yet.

I have a MKR1000 and an  Adafruit "Bluefruit LE SPI Friend" with the intention of modding an IBM Model M to be both USB and BT enabled.  I've seen the Teensy mods (https://www.pjrc.com/teensy/) but after doing some reading, it appears that there's more to it than just hooking the pins up to the MKR1000.  Things such as N-key rollover and/or key shadowing are apparently a thing that take some workarounds.

Has anyone modded a Model M this way that can speak to how easy/hard that is, or point me to a better reference?

Or should I just get the Teensy and add the BT option after getting it to work as a USB keyboard?

Thanks,

Dan

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[Kevin Fusselman]

I did a conversion a number of years ago, and just buried one of those cheap ebay ps/2 to usb adapters inside. It doesn't do Bluetooth, but it's an option...

For those who don't remember things before usb, ps/2 keyboard was a standard pioneered by the IBM computer of the same designation to replace the larger AT keyboard connection (which was a DIN5 connector, compared to ps/2's MINI-DIN6).

Most ps/2 gear was backwards compatible to the older standard, with an appropriate plug adapter.

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[andrew....@gmail.com]

It depends a little bit on which Model M you have (AT, XT, terminal, ps2, etc), but probably what you're looking for is Soarer's converter if you just want to plug it into a USB socket:

https://deskthority.net/workshop-f7/xt-at-ps2-terminal-to-usb-converter-with-nkro-t2510.html

https://geekhack.org/index.php?topic=17458.0

And if you want a cheap (~$5 on ebay) alternative Teensy 2.0 alternative that still uses the ATmega32u4 chip, check out:

https://deskthority.net/wiki/Arduino_Pro_Micro

If/when you're feeling ambitious past that, here's a good walkthrough about how to get bluetooth into the mix:

https://learn.adafruit.com/convert-your-model-m-keyboard-to-bluetooth-with-bluefruit-ez-key-hid/overview

When you're talking about "shadowing", I think you're referring to what I know of as "ghosting", which are erroneous key registers caused by multiple simultaneous keypresses (ghost letters showing up), something which isn't really a concern with modern keyboards. The practice of preventing these "ghost keys" from showing up is to block input after a second key is pressed (known as "blocking"), so if you "roll over" more than two keys, only the first two register -- 2 Key Roll Over (2KRO).

NKRO, 6KRO, & 2KRO are references for how many keys can be pressed simultaneously and still register. Whereas cheap rubberdome USB keyboards usually crap out after "rolling over" just two keys -- the aforementioned 2KRO -- good USB keyboards will go all the way up to the max of the USB standard, which is 6 simultaneous keypresses (6KRO), and really good USB keyboards use a combination of sneaky code and dark magic to be able to register an "n" number of simultaneous keypresses where "n" is any value you can manage to push while rolling your face back and forth across the board to test it (NKRO). The PS2 standard natively supports NKRO, which is why you'll frequently see higher-end keyboards come with a USB -> PS2 adapter included.

The deskthority wiki has a much more exhaustive writeup of it:

https://deskthority.net/wiki/Rollover,_blocking_and_ghosting

[andrew....@gmail.com]

For anyone looking into this and will need switches, massdrop has them for cheap right now. 120 for $31.74 shipped.

Just be aware that the Gateron color scheme does not always match the Cherry color scheme for switch type (Gateron Clears are linear, for example, not tactile).

https://www.massdrop.com/buy/gateron-switches