With touchscreens slowly getting integrated into every aspect of our technologically focused lives it’s kind of surprising that we have stuck with the old mouse and keyboard for so long.
There are several touchscreen technologies available. Most modern phones use capacitive touch where an underlying transparent network of contacts detects the change in capacitance from a finger. While this system is great on small devices it doesn’t scale well. It also means the screen can only be operated by a finger (or suitable capacitive stylus) and won’t work with gloves.
Older devices tended to use resistive touchscreens. These used pressure to physically make contact within layers on the screen. While cheap and easy to produce they are sometimes unresponsive need a fair bit of force and don’t generally handle multi-touch.
Some high-end screens use acoustic sensing where focused ultrasonic waves flow over the LCD surface. Placing a finger or other object on the screen blocks and reflects the sound letting the computer calculate exactly where the finger is placed. Large device touchscreens such as the Microsoft surface use cameras to directly process inputs to a screen.
Typically touchscreen AIO PCs and add-on monitors use an optical sensing method. Infra-red LEDs beam light across the surface of the display where it’s picked up by opposing sensors. Placing a finger or other object on the screen blocks the light letting your PC calculate exactly where the screen is being touched. This setup also allows multi-touch as the system can easily track multiple contacts. While fast and accurate optical sensing can be disrupted by sunlight or other high intensity IR sources.
While screens typically come with built-in touch sensitivity it’s also possible to buy add-on kits. This can work in a number of ways though the most popular is still optical sensing.