The ZMK Uno shield is an OSH shield for the Arduino Uno Rev3 interface, making it compatible with any compatible dev kit, such as the Nordic 52840 DK, ST Nucleo 64 kits, etc.
The goal is to create a standard hardware target for testing and development of ZMK, as well as a supported sample hardware for anyone to evaluate ZMK's feature before committing to use it for their designs.
The ZMK Uno has the following goals:
- Include all commonly found ZMK keyboard hardware
- Allow adding additional hardware beyond that for further development.
- Be low cost
- Be hand solderable, or possible to get mostly assembled by JLC and other budget manufacturers
The goal of ZMK Uno is to contain the common, or actively supported hardware found on the many keyboards, while also offering continued expansion (e.g. using a half-width shield/hat over it) for addition custom hardware to be developed/tested.
ZMK Uno contains 4 switches (one of which is an EC11 encoder w/ click functionality), that can be configured either in a 2x2 matrix, or 4-wire direct wire confugration using the jumper in the lower left corner.
A single EC11 encoder is included, allowing testing of encoder/sensor behavior in ZMK.
Many wireless designs (e.g. nRFMicro, nice!nano) include the ability to cut off the VCC power to save power, especially for keyboards with addressable RGB LEDs which have a high quiescent current. The ZMK Uno shield includes two MOSFETs, creating a toplevel "power domain" that both the SSD1306 OLED and second MOSFET are connected two. The second MOSFET is a "sub-power domain" of the first one, and contains the RGB LEDs for the underglow and per-key LEDs. Doing so allows testing more complex power domain scenarios, and allows you to cut power to the RGB while still allowing the OLED to stay powered. The second MOSFET can also be ignored since its default state is open, and you can treat the system as just having on toplevel power domain, which matches devices like the nice!nano, nRFMicro, etc.
Two reverse mount LEDs are included, below the encoder, that indicate the main and sub-domain power status. If testing power efficiancy, JP2 and JP3 on the back can be cut to remove the current draw from those LEDs.
A standard header for the common SSD1306 i2c OLED modules is including, allowing testing of the ZMK display functionality.
The display VCC pin is connected to the VCC line behind the toplevel power-domain. Optional I2C pull ups can be set by soldering JP5 jumper on the back.
TODO: Document SPI display support for
Both underglow, and per-key RGB LEDs are included in the ZMK Uno shield. Currently, only underglow is supported by ZMK, but the per-key RGB hardware is included for possible future development/testing.
All LED power pins are connected to the RGB sub-power domain for their power.
TODO: Document hybrind WS2812B footprint
Single color backlight is also supported. This is controlled by a dedicated MOSFET, and is connected directly to VCC, not through any sub-domain. The backlight LEDs are not under the keys, but instead pointing downwward onto the host board.
ZMK does not currently support wired split designs, however to support any future efforst to add that support, the ZMK Uno includes a standard TRRS jack, which can be configured using pin jumpers to use either serial or I2C pins. In addition, an optional pull up can be enabled with a jumper, for testing single-wire half duplex serial mode.
An optocoupler is included that allows for connecting an external device (e.g. Raspberry Pi) to trigger SW1 while measuring time to receieve the corresponding input to the same device. The eexteral device should be connected to the SW1 TRIGGER/GND in the top left corner, and the TRIGGER pin should be set high to trigger a press of SW1. The hardware was designed following this guide but the software to use this has not been fully tested/documented.
ZMK Uno uses KiCad nightly. After fetching the repository, be sure to run:
git submodule update --init
To fetch the various footprint libraries used by the project.
| Quantity | Description | LCSC # | Mfr Part Number |
|---|---|---|---|
| 3 | Kailh Hotswap Socket | N/A | CPG151101S11 |
| 3 | MX Switches | ||
| 1 | Rotary Encoder | EC11 | |
| 4 | Diodes | C81598 | 1N4148W |
| 3 | Switch Mode Selection Headers | 1x8 2mm pitch pin headers | |
| 1 | Reset Button | C79174 | EVQPUC02K |
| 11 | Pin Jumpers For Mode Selection | 2mm-pitch pin jumpers (e.g. SPN02SXCN-RC) | |
| 1 | Direct/martrix selection IC | C2673317 | TS3A27518EPW |
| 1 | LED Resistor | 500Ω (0805) | |
| 1 | Power Cutoff Resistor | 2MΩ (0805) | |
| 1 | Power Cutoff MOSFET | C15127 | AO3401A |
| 4 | Underglow RGB LEDs | C2761795/C965555 | WS2812B/WS2812B-2020 |
| 3 | Per-Key RGB LEDs | C9900001298 | SK6812MINI-E |
| 1 | I2C Pullup Header | 1x2 2mm pitch pin headers | |
| 2 | I2C Pullup Resistors | 10kΩ (0805) | |
| 1 | 128x64 I2c OLED Module | ||
| 1 | TRRS Pin Selection Header | 1x4 2mm pitch pin headers | |
| 2 | TRRS Pin Selection Headers | 1x2 2mm pitch pin headers | |
| 1 | TRRS Jack | PJ320A | |
| 1 | Latency Tester Resistor | 150Ω (0805) | |
| 1 | Latency Tester Optocoupler | C106900 | EL817S1 |