isometria⁷⁵

The first prototype is sitting on my desk and works perfectly - clearance for weights and battery is currently wrong, so the intended battery will not fit in the case.

The name isometria⁷⁵ has it's origin in the greek noun ἰσομετρία (in latin letters: isometria), meaning "equality of measure" [1]. This word ended up being included in various languages, among them english (isometric), with the same meaning. I chose it for two reasons - because this keyboard is only available in an ISO layout (sorry ANSI users - for once it is ne ANSI avail), but also, because I paid attention to only use u/4 spaces throughout my board. You will have a hard time finding any distance on it that's not a multiple of 4.75 mm.

Features

• CNC'd top shell with integrated 3 mm plate (obviously, with cutouts for switch retention and PCB mount stabs)
• 6.8° typing angle
• The PCB is equipped to fit 82 cherry MX-style switches
• One 3 mm LED per switch (monochrome, dimmable only as one group)
• 17 SK6812 Mini can be soldered to the bottom of the board for underglow
• Fits either a battery-management or a simple USB-C daughterboard (Repo link)
• A rotary encoder sits in the top right corner and the push-button is wired to the controller (Row 0 Column 15)
• The USB-C connector is placed on a small PCB on it's own, which can be replaced by a battery management board
• Sense wires to measure the input voltage and to check if the battery is currently being charged
• A STM32F072CBT6 controller with native crystal-less USB and a lot of IO for various things
• An SPI interface is wired to a second connector, allowing for a SPI Bluetooth LE board to be added
• One leftover GPIO is available on a header - if you want to add something yourself

Design

The PCB uses a key spacing of 19 mm (instead of the default 19.05), and all delimiters between key-blocks, or keys and the border of the case are 4.75 or 9.5 mm wide. This allows for a pleasantly homogenous design, which earned the keyboard it's name. Sadly, this layout requires a 1.5u right shift, which very few sets include.

The bottom shell breaks the minimalist design of the top shell a little, with "stepped" faces. While the design originated from the need to make it easily millable on a 3 axis CNC, I appreciate the fact that it makes the board visually a bit more interesting.

Geekhack project thread

https://geekhack.org/index.php?topic=106060.msg2896354

FAQ:

• Where can I buy this?

  I'm afraid there will not be any groupbuy nor will it be stocked at some reseller - All files are open source though, feel free to order a batch of PCBs and a case yourself - or improve it!

• When will there be an ANSI version?

  Even though I planned not to do ANSI, I actually went with multi-layout for v2! Stay tuned!

• Why did you clone the Evolv/Satisfaction?

  I made my own design choices, and designed everything from scratch - however the evolv heavily influenced my design. I fell in love with it the first time I saw it, but it had a few things I dislike. So I decided to mostly adopt it's layout with some changes, and design a case which follows my design ideals - ending up with a (visually) very similar top enclosure - The standalone-features of the evolv are it's premium materials, construction and generative design, and I did not include either.

For any other questions, or problems with my board (if you decided to build one yourself) - feel free to contact me. I'm idling around and occasionally check my PMs on freenode (ebastler), am active on reddit (the_ebastler) and on discord (ebastler#8966).

Big thanks to:

• ai03 for both his great tutorial as well as his various footprints I used in my design - I don't know if I had been able to design this without his help.
• The awesome people on grabcad for the MX switch, Cherry Stab and pushbutton models, JST SH models and WS2812 Mini models which made my design a whole lot easier, and my renders prettier.
• People on the MechKeys and Mechanische Tastaturen Deutschland discord servers who tirelessly answered my questions - from the noobiest to the most complicated ones.
• Propagandalf1 for all the advise, criticism and ideas for improvement
• Pseudoephedrin and Lux for checking my PCB layouts for errors
• Hendrik for milling my proto