There are multiple touchscreen technologies available for LCD monitors, Panel PC or tablet PC. The choice depends on the usage and environment. Here is a simplified presentation to compare the main caracteristics of touchscreen technologies. This document does not intend to present all technologies available.
BOLDindicates the most common touchscreen solutions used in professionnal solutions
It is the most common and a cheap solution. It consists of 2 thin films that touch each other when pressure is applied. Any pressure above the minimum required can be detected : finger, plastic made passive stylus. Without pressure, the 2 films do not touch - they are separated by small balls. The touchscreen surface must be aligned with the display image - this is called "calibration". Calibration is fairly stable with resistive technology. Over time, re-calibration may be required - it is done with a calibration software. The resistive films absorb around 20% of the light emited by the LCD panel, the display brightness is reduced up to 20% compared to the same display without resistive touchscreen.
Resistive touchscreen can be damaged, i.e. scratched or cut. They cannot be used in public environment with the risk of vandalism.
The pressure needed to be detected varies:
- 40 grammes high sensitivity,
- 80 grammes sensitive to finget touch,
- 120 grammes hardly sensitive to fingers, need a stronger pressure such as stylus pens.
4 and 8 wires resistive touchscreen are less durable than 5, 6 or 7 wire versions that are recommended for frequent usage.
NOTE: resistive touch is available up to 22'' display sizes
This technologie relies on a conducting film on the screen. The change of electrical capacity is detected by the film; the contact of a finger is detected since the human body has an electrical capacity. A finger in a glove is not detected, nor is a passive stylus.
The surface capacitive film is sensitive to scratch, and absorbs a small part of the LCD light. The calibration must be redone from time to time to maintain the alignment touchscreen / display.
The projected capacitive is between 2 glass layers. Once again, it detects fingers not inside gloves. It is not sensitive to scratch and can be used on vandal-proof tempered glass.
Some versions are available to be sensitive through thick galsses, and provide the capability to place a touchscreen behinb a storefront window up to 8mm thick.
Capactive touchscreen must not touch metal, therefore, joints are applied to integrate touchscreen into metal chassis such as industrial panel PC or LCD.
MultitouchCapacitive is known to provide multitouch version, which is also available in some resistive touchscreen
Surface Accoustic Wave
This technology uses the sides to detect the touch location - the same way as SAW. The glass surface is inactive; the sides detect the "X,Y" location when IR rays that are "cut" - LED are situated inside the frame (IR emission LED, reception). The contact on the surface must be large enough to be detected: a finger is detected, a stylus is too thin to be detected. This is suitable to touching navigation buttons; handwriting recognition is not possible.
Digitizers were originally in every tablet PC as standardized by Microsoft in 2001. The pen is active and detected by the digitizer. No pressure is detected, therefore you can lay the hand on the display while writing.Digitizers can be combined with resistive touchscreen for instance - either one is active at one point in time.
Both resistive and capacitive can be sealed to provide IP65 and higher protection, up to Atex.
IR and SAW can reach IP54 protection, for higher protection, resistive or capacitive touchscreen are required.