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keyboard-friend · One Press to Trigger Your Commands

Introduction

This is a simple and practical macro keyboard. What makes it special?

• Configuration-friendly – No additional driver installation required
• DIY-friendly – Few parts, easy to buy and assemble
• Cross-platform – Supports Windows, Linux, and Android

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Hardware & Firmware

For experienced users, it is recommended to purchase components and build your own.

For those who want to directly experience the features, it is recommended to purchase the ready-made product (coming soon), and you can skip the "DevHardwareice and Firmware" section.

Component	Description	Price (CNY)
4×4 I2C Matrix Keypad	16-key layout, supports I2C comms	14
nRF52840 ProMicro	Main controller board	12
USB Type-C Cable	Power + data transfer	-

Note: Flashing firmware also requires J-Link/DAPLink or other general-purpose firmware development devices

4×4 I2C Matrix Keypad

nRF52840 ProMicro

Hardware Wiring

4×4 I2C Matrix Keypad	nRF52840 ProMicro
VCC	VCC
GND	GND
SCL	P0.27
SDA	P0.26
INT	Not Connected

Host USB Port <--USB Cable--> nRF52840 ProMicro Type-C

Flashing Firmware

Download the firmware and flash it via J-Link

If you're not familiar with J-Link command, you can use nRF Connect for Desktop (Programmer app), or ask AI "How to download hex format firmware to nrf52840" :)

For the firmware list, see Releases.

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Quick Start

Get started in two steps

Configuration Mode – Edit the config file to set the keypress content you want

Press the * key three times in a row to trigger mode switching. In "Configuration Mode", the device will be recognized as a USB drive on the host. Open the USB drive and modify/create the config.json file.

config.json file field descriptions:

• name: Configuration file description, can be any text
• 0-9, A-D, *, #: Mapped to custom strings
  • Supported: Letters (a-z, A-Z), numbers (0-9), common symbols (- _ @ # $ % ^ & * etc.)
  • Supported special characters: \n (newline), \t (tab), \b (backspace)
  • Does not support multi-byte characters such as Chinese, Japanese, emoji
  • String length ≤ 64 bytes
• Multiple backup configuration files can be stored (e.g., config_mode1.json, config_mode2.json, ...), but only config.json will be loaded

Example

{
    "name": "keypad_config_v1",
    "0": "hello 0",
    "1": "hello 1",
    "2": "hello 2",
    "3": "hello 3",
    "4": "hello 4",
    "5": "hello 5",
    "6": "hello 6",
    "7": "good 7",
    "8": "good 8",
    "9": "good 9",
    "A": "good A",
    "B": "good B",
    "C": "good C",
    "D": "good D",
    "*": "good *",
    "#": "good #"
}

Working Mode – Connect the device and press the corresponding keys to trigger

Press the * key three times in a row to trigger mode switching. In "Working Mode", the device will be recognized as a keyboard on the host. Press a key in any text input field to output the corresponding content.

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Template Configuration

Switch to "Configuration Mode", copy the configuration to the device and name it config.json, then switch to "Working Mode" to use it.

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Limitations

• Does not support Chinese character input
• Does not support wireless connection (requires wired use)

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Thanks & Open Source

The project pays tribute to classic games. Forks and PRs are welcome. Apache License © 2026