Whatever software you decide to use, it will require a key matrix that maps out how your keyboard is wired. If you would rather write your own keyboard software using Arduino, the Teensyduino functions give you total USB control.
The TMK code is a bit of an overkill if you just want a simple USB keyboard but it will certainly provide all the features you could ever need. Teensies are often used by the mechanical keyboard enthusiasts at Geekhack and Deskthority and the TMK software is the most popular controller code. I use a Teensy microcontroller mounted on a connector board to take over this function. A typical laptop keyboard relies on the motherboard for the keyboard scanning and touchpad interface. I created this guide and video to hopefully make it easier for people to re-purpose an old laptop. This Instructable will provide a step by step procedure for building a USB laptop keyboard and touchpad controller.
