Kermite firmware library for Arduino and PlatformIO.

You can create a Kermite-compatible keyboard firmware with Arduino.

Here the process instructed how to create a keyboard firmware in Arduino.

In this tutorial, a single-key keyboard firmware is created with the board based on RP2040.

Prepare a development board with RP2040. For this tutorial, the boards listed below are supported.

• Raspberry Pi Pico
• Adafruit KB2040
• Seeed XIAO RP2040
• RP2040 Zero
• Tiny2040

If you don't have them, other RP2040 boards can also be used if you change the pin settings.

As an example, I set up a board like this with KB2040.

A tact switch or key switch is connected to a pin. The port is detailed later.

First, install Arduino IDE if you don't have it. You can download installers from here. https://www.arduino.cc/en/software

Launch Arduino IDE.

3rd party RP2040 based board is not supported officially by Arduino. A board package forked from arduino-pico (earlephilhower) is used here. It is modified to support USB RawHID feature and has some adjustment to make it easy to create a keyboard firmware.

From File > Preferences in main menu, open the configuration panel.

In Additional board manager URLs field, add the URL below.

https://github.com/kermite-org/arduino-pico/releases/download/global/package_rp2040_index.json

By this configuration, a custom board package is indexed and can be installed from package manager UI.

Open board manager tab from left side navigation.

Search rp2040 and find the package Raspberry Pi Pico/RP2040 by Earle F.Philhower,III . Select the latest kermite-fork-* suffixed version in the list and install it.

There are two libraries provided to create a keyboard firmware for Kermite.

The library KermieCore_Arduino is a firmware core library. It handles keyboard layer logic and has USB HID device implementation. Communication to the Kermite's web application is also handled in this library.

keyboard_peripheral_modules is an optional library to be used to make a keyboard firmware easily. A basic key matrix scanner class and onboard LED abstraction class are included.

Open library manager from sidebar.

Search kermite and install these libraries.

When you install keyboard_peripheral_modules, a popup asks you whether to install dependent modules. Select INSTALL ALL here.

Here we'are going to run a basic example provided in the library.

Open an example sketch from File > Examples > KermiteCore_Arduino > basic.

Select a target board from Tools > Board > Raspberry PI Pico/RP2040. Most of the RP2040 is covered here, but if your board is not in the list, select Generic RP2040 in the bottom of the options. This is a generic board definition and can be used for any boards.

There is a code block to setup onboard LED and an input pin definition for the button.

//select an appropriate boardLED initializer for your board
//BoardLED boardLED(25); //pico
//BoardLED boardLED(18, 19, 20, true); //tiny2040
BoardLED_NeoPixel boardLED(17, 0x40); //kb2040
//BoardLED_NeoPixel boardLED(12, 0x40, 11); //xiao rp2040
//BoardLED_NeoPixel boardLED(16, 0x40); //rp2040-zero

Comment in a boardLED initializer according to your board.

BoardLED is a class wraps up to 3 LEDs on the board. BoardLED_NeoPixel is wrapper module for onboard NeoPixel LED to provide the interface as if it is looked as 3 individual LEDs.

If you want define a custom boardLED instance, refer the constructor signature below.

  BoardLED(int pin0, int pin1 = -1, int pin2 = -1, bool sink = false);
  BoardLED_NeoPixel(int pin, int brightness = 0xFF, int powerPin = -1);

In the code, the pin number is corresponds GP0-GP31 ports of RP2040. Not for the pins D0,D1,D2... labeled in some board.

  const int pinButton = 6; //set an input pin for your board

Select a pin number which is connected to your input button. It has pull-upped internally and no extra pull-up needed.

If the board is used with a firmware not compatible to arduino, it is required to reset the board manually. Make the board bootloader mode and upload the sketch.

Make the board entered into bootloader with the buttons on the board. Press and release RESET button while holding BOOT button.

Select UF2 Board in the board menu.

Press Upload button.

Once a firmware based on arduino has written to the board, A virtual COM port is exposed to provide software reset feature. Using this, you don't have to reset the board manually.

Select the com port in board menu for the board.

Press Upload button.

Check the firmware works as expected.

Onboard LED shortly lights once per second to show the program is going well.

If you press the button, onboard LED lights in another color. If a keymapping is written by webapp, letters are emitted.