Build a Hardware Macro Keyboard

The newest issue of Mac & I features an article about building a programmable keyboard. The article is behind a paywall and in German, but can help you out:

Getting started with microcontroller programming: DIY macro keyboard
For little money you can build a macro keyboard to send commands or text modules to Mac or PC. We show step by step how it works.

Getting started with microcontroller programming has never been as cheap and easy as it is today - thanks to Arduino. After completing the project, you tap one of the 16 keys on an external keypad to run a custom keyboard macro and send it to macOS or Windows programs, just as if a regular keyboard were connected that you'd have to operate by hand. This way you can, for example, put special characters hidden in the shallows that you need more often on a key or insert complex text modules with one tap. This is made possible by microcontrollers that connect to the computer like a USB keyboard.

Input devices like keyboard and mouse are nowadays connected either via USB or Bluetooth LE. Conveniently, both use the HID (Human Interface Device) protocol, which was originally conceived for USB. All current operating systems recognize HID devices like keyboards and mice without requiring a special driver.

If you already have basic electronics equipment, especially a soldering iron, you can build your own individual macro keyboard with USB or BLE for very little money with our instructions. If you want to buy a soldering device, you should not save too much money - even if the work for our project is limited to soldering rows of pins. A soldering iron is suitable for many other projects.