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The Liatris is a new controller designed by splitkb.com that's a designed specifically for (split) keyboards. It's a drop-in replacement for the Pro Micro, and a perfect alternative for other RP2040-based controllers.

Core features

• Designed for maximum compatibility with kits that work with Pro Micro controllers, including the Kyria and our Aurora Series.
• Supports QMK (all capabilities) and ZMK firmware (wired, single controller) out of the box. Also compatible with KMK and CircuitPython.
• Has 128Mbit (16MB) of flash memory, ensuring you'll never run out of space even when making heavy use of OLED animations or text expansion macros. We added as much flash as the RP2040 can handle!
• Access to 23 GPIO pins to use on your keyboard, meaning that on any Aurora Series keyboard, you'll have 5 pins left over for any modifications you may want to do.
• Rear-facing bootloader button allowing you to easily recover from a bricked firmware, even when mounted in the usual upside-down position.
• An ultra-low profile with a mid-mounted USB-C port and a mere 1mm thick PCB. The rear-mounted reset button checks in at only 0.35mm, too, like it's almost not there.
• Supports at least 1A of power output, so you can maximize the output of your LEDs when your computer outputs enough power.

Advanced features

The default settings are right for most people out of the gate. For those who demand more of their controller, we have some advanced features:

• Runs at 3.6V for better 5V signal compatibility so your LEDs will listen better to those smooth colour change commands (according to data sheets, 3.5V is the minimum to reliably talk with LEDs);
• Selectable voltage on the VCC (defaults to 5V to support RGB LEDs) and RAW pins (which we named VA, and isn't connected by default to be compatible with common Corne-style kits that bridge VCC with RAW on the keyboard by default) for when you need to get specific with your kit;
• USB data pads for hand wired builds where you want to have a separate USB port somewhere else on the board;
• Debug pads to be able to better look into microcontroller behaviour when you really need to.

Frequently asked questions

• Question: On a split keyboard, can I use a Liatris as the main controller and a Pro Micro/Elite-C as the peripheral?
• Answer: You can not. They aren't compatible with one another. You can, however, use another RP2040 controller as either the main or peripheral controller, like the Elite Pi.
• Question: This controller has a voltage of 3.6V. Why's that?
• Answer: A common option used on split keyboards are addressable RGB LEDs. These operate on 5V logic. According to the manufacturers of these LEDs, the minimum voltage needed to talk to them reliably is 3.5V, which the standard 3V3 would be just shy of. We thus increased the voltage of our controller slightly to be able to interact with 5V logic devices more reliably. Other controllers may work, but they do work outside of the specifications.
• And don't worry, 3.6V is still well within the specifications for the RP2040 chip that powers the Liatris. It is not detrimental to its performance over time.
• Question: Why would I need 128Mbit of flash space?
• Answer: Many controllers have 16Mbit (2MB) of space. A common firmware file only takes up 80KB (0.08MB), meaning you'll have plenty of space regardless of the controller you choose.
• As an example: On a black and white display, each pixel takes a bit of data. For a 128x64 display, one frame takes up about one KB, so you can store roughly 1900 frames alongside the rest of the firmware on a 16Mb controller. If you'd use a colour display instead, storage would take three bytes per pixel instead of one bit. That's 24 times as much data required for the same frame, and so with the same space, you could store 80 colour frames. The Liatris has 8 times as much memory, so you could store around 15.900 black and white images or 660 colour images on it for a 128x64 display!
• So, purely for the space: you'll want this controller if you want to play a movie on it, store and play back sound files, or maybe make and play games on it!

Remarks

• While the I2C pins are 5V tolerant, they don't like a direct short to 5V. Pulling them up to 5V with resistors is supported, though, which is the primary use in keyboards.
• While the I2C pins are 5V tolerant, take care to not put 5V onto the other IO pins. They won't like that! When using this controller with kits sold at splitkb.com, this scenario won't happen. With other kits, it also likely won't happen, but it can't hurt to check.

Read more

• How to turn off the Liatris' power LED
• How to control the Liatris' RGB LED
• Why would I want to socket my microcontroller? for reasons why you could choose to socket your microcontroller.