Old laptops are ripe for hacking, and are a great source of high-quality components. The second a laptop gets even slightly out of date, its monetary value plummets incredibly quickly and you can get one cheap. The most common part to salvage from a used laptop is the LCD, which can be integrated into your projects through an LCD controller. But there are still lots of other parts in there, and YouTuber Tinkernut will show you how you can upcycle the touchpad to use as an input for your Arduino.
Tinkernut, AKA Daniel Davis, starts by explaining how most of those laptop touchpads actually work. The vast majority are capacitive touchpads, which means they calculate the position of your finger by measuring changes in the capacitance between points at the corners of the touchpad. By calculating the distance from multiple points, the touchpad can triangulate the position of your finger. In Tinkernut’s case, those coordinates are then sent to the computer via an old school PS/2 interface.
The cable is unique to the laptop, but that PS/2 interface is the same as what you’d find on an old pre-USB mouse. It’s a well-documented interface, and is widely supported. There are even Arduino libraries that you can use to connect to a PS/2 mouse. Tinkernut illustrates how he was able to take advantage of that to control the servos on a robotic arm, with the X coordinates controlling one servo and the Y coordinates controlling another. But, you can utilize the same basic process to integrate your upcycled touchpad into any other project you can imagine.