Note about Touch screen technologies:-  

There are a number of Touch technologies available with regard to touch screens, in the main these are Capacitive, Resistive, Infra-Red, SAW and optical. Typically for touch screen monitors smaller than 30 inch the main stream touch technology available is either Capacitive or Resistive.

Capacitive touch screens are more robust as they normally use a Glass screen surface which is normally bonded on top of the actual LCD surface, and are resistant to scratches and general wear and tear. Capacitive touch screens are coated with a material that stores electrical charge. When the monitor is touched by a human finger, a portion of the charge is transferred to the user, decreasing the panel’s capacitive layer. Electronic circuits then measure the ensuing alteration and calculate where the touch event happened.

Capacitive touch screens do not work with gloved hands, or stylus, however they are more robust and generally last longer than Resistive types.

Resistive touch screens employ two layers, a conductive and a resistive metallic layer which are held apart by miniature spacers. An electrical current runs through the two layers and when a users touches the screen, the two layers make contact in that exact spot. The change in the electrical field is noted and the coordinates of the point of contact are then calculated by the touch sensor.

Resistive touch screens work with human finger, gloved hands and stylus, however repetitive touches on the same spot can wear out the contacts over time. Care also needs to be taken with resistive touch screens to avoid scratching the surface which can damage the matrix of contacts rendering the screen inoperable to touch.

Infra Red touch screens are normally found on larger displays 30 inch +, with IR touch screens there are IR LED transmitters that produce beams of IR light, and IR sensors that detect these beams, when the beam of light is broken by touching the monitor this is detected and turned into the touch point coordinates. IR touch screens are fine for general applications however caution needs to be exercised when used within a TV studio environment, due to interference from the IR generated by studio lights.

SAW technology (Surface Acoustic Wave) touch screens use two tranducers (one for sending and one for receiving) that are placed along the X & Y axes of the monitors glass plate. Also placed on the glass are reflectors (which reflect an electrical signal sent from one transducer to the other). The recivieng trandducer is able to tell if the acustic wave has been disturbed by a touch event at any instant and generate a coordinate to locate the touch.

Optical touch screens use scanning optical cameras to sense a 2-dimensional field which when interrupted by a touch is calculated to a X/Y coordinate. Optical touch screens are robust and can be used with gloved hands, stylus, human fingers and do not suffer from calibration drift. They are generally found on larger display screens 20 to 60” +.