TOUCHSCREENS  

Four common touchscreen technologies are used with tablets, watches, and mobile phones:

• Resistive
• Capacitive
• Infrared
• Surface Acoustic Wave (SAW)

Resistive touchscreens

• Resistive touchscreens are made up of a layer of conductive polyester and a layer of conductive glass
• The two layers are separated by an insulating membrane
• When the screen is gently pressed by a finger, the two conducting layers make contact and complete a circuit
• The position where the screen is touched is calculated by a microprocessor

Capacitive touchscreens

• Capacitive touchscreens are made up of glass layers
• The bottom surface of the upper layer and top surface of the bottom layer are coated in perpendicular lines of transparent conductive material (Indium Tin Oxide) forming a grid
• The screen behaves like a capacitor, storing electrical energy
• The screen can be touched in more than one place at a time

Detecting touch

• When the screen is touched by a finger, there is a change in the electric field at that position
• The position where the field changes is calculated by a microprocessor

Infra-red touch screens

• Infra-red touch screens use a grid pattern of LEDs and photocells (light sensors)
• LEDs shine infra-red light in front of the screen
• When the screen is touched by a finger, the infra-red beam is interrupted
• A microprocessor calculates the coordinates of where the screen was touched

Surface Acoustic Wave screens

• Surface Acoustic Wave touchscreens make use of ultrasonic sound waves
• Two sound wave transducers (which generate the ultrasonic sound) and two receivers are used; the sound waves travel parallel to the edge of the glass vertically and horizontally
• The position where the screen is touched is detected by a reduction in the sound wave amplitude

Interactive whiteboards

• Interactive Whiteboards are used to show audiences at meetings or classroom students, computer output
• They allow the user to use the board as a touchscreen or write over the screen to create annotations
• At the end of the meeting, hand annotations can be saved along with the screen image for future reference