How touchscreens work

How Does a Touch Screen Work?
A touch screen has three main components: a touch sensor, a controller, and a software driver. The touch screen itself is an input device, so it needs to be combined with a monitor and a PC to make a complete touch input system.

Touch Sensor

There are a number of touch screen technologies on the market today. Each uses a different method to sense touch input. Often these are a plastic or glass panel placed under the bezel of the LCD screen.

Touch Controller

The touch controller is a small PC card that connects between the touch sensor and the PC. It is usually installed inside the touch monitor. The touch monitor will have an extra cable connection on the back – usually USB or serial (RS-232) that connects directly to this board. The touch controller takes information from the touch sensor and translates it into information that the PC can understand.

Touch Screen Software Driver

Our touch screen monitors and kiosks are supplied with touch screen software drivers that allow the touch screen to emulate the left button click of a mouse.  Installing the software is usually a quick process consisting of running the installation file. Most users find that they simply accept the defaults, and installation normally just takes a few moments.

Once the touch screen driver software is installed, touching the screen is the same as clicking your mouse at the same point on the screen. This allows the touch screen to work with a vast amount of pre-existing mouse driven software. This also allows for simple development of new applications, because no additional code or knowledge is required to develop software for use with the touch screen. New touch screen applications can be developed in the same way as mouse driven software.  The touch screen can emulate left-clicks, double-clicking, and dragging. When the screen is touched, it is the same as if you used your mouse to move the pointer to that spot, and then clicked your left mouse button.
Resistive touchscreens - which are used on some Samsung, HTC and LG phones, and are typical of ATMs, supermarket checkout stations and the electronic signature doodad the UPS guy carries - have a glass panel that’s covered with conductive and resistive metallic layers. These two layers are held apart by spacers, and an electrical current runs through them when the screen is operational. When a user touches the screen, the two layers make contact in that spot. The change in the electrical field is noted and the device coordinates the point of contact so a device driver can translate user touches and movements into something that the OS can understand.

Capacitive touchscreens - used on the iPhone, Droid Eris and Blackberry Storm, among other smartphones - have a glass screen covered by a transparent conductor layer that stores an electrical charge. When a user touches a finger (which is also conductive) to the screen, the electrical field distorts and the device uses that to figure out where the screen was touched and relays the info to the driver.

The big drawback of capacitative screens is that they don’t work well, or at all, when the user's fingers are covered by electrically insulating material, like gloves. If the choice between cold hands and using your phone is a hard one, you can get around the issue by buying gloves that have conductive threads woven into the fingertips, or by making your own.