How do touchscreens work?

3 BASIC SYSTEMS:

• Resistive
• Capacitive
• Surface acoustic wave

• In the capacitive system, a layer that stores electrical charge is placed on the glass panel of the monitor. When a user touches the monitor with his or her finger, some of the charge is transferred to the user, so the charge on the capacitive layer decreases. This decrease is measured in circuits located at each corner of the monitor. The computer calculates, from the relative differences in charge at each corner, exactly where the touch event took place and then relays that information to the touch-screen driver software. One advantage that the capacitive system has over the resistive system is that it transmits almost 90 percent of the light from the monitor, whereas the resistive system only transmits about 75 percent. This gives the capacitive system a much clearer picture than the resistive system.

In the picture it is shown how when an area of the screen is touched it is triangulated back to the sensors in each corner.



• After the voltage change has been located, a controller transforms this input into something that a computer can understand.

• Finally, a software driver tells the computer how to interpret the "touch information" that comes from the controller. This is what makes it possible for some devices like the iPad to recognize "multitouch gestures" which consist of more complex things than simply tapping the screen, like for example pinching (to make zoom) or dragging objects.

Picture shows multitouch, when more then one point on the screen is touched which is often used for zooming or multitasking.