Touch Screen!...

A touch screen is a computer display screen that is also an input device. The screens are sensitive to pressure; a user interacts with the computer by touching pictures or words on the screen.

4-WIRE RESISTIVE SCREENS (PL AND FG)

The 4-wire Resistive Touch Screen consists of a conductive bottom layer of either glass or film and a conductive top film layer, separated by extremely small, transparent spacer dots. A voltage is applied across the conductive surface. Any type of probe, including fingers, gloved fingers, credit cards, pens, etc., that can be used to apply pressure against the top film will activate the screen. When ample touch pressure is applied to the top layer, the film flexes inward and makes contact with the bottom layer resulting in a voltage drop. This change in voltage is detected by the controller. By alternating the voltage signal between the top and bottom layer, the X and Y coordinates of the user’s touch are computed. In a Film on Glass (FG) construction, the bottom layer is an ITO coated glass. In a Polyester Laminated (PL) or film-film-glass construction the bottom conductive layer is polyester. An additional layer of Optically Clear Adhesive (OCA) bonds the bottom polyester layer to a backer typically made of glass or poly material.

5-WIRE RESISTIVE SCREENS (FG AND GFG)

Similar to the 4-wire technology, the 5-wire Resistive Touch Screen also consists of a conductive glass bottom layer and conductive top film layer. Designs are also available with a durable top glass sheet (GFG). The fundamental difference is, in the 5-wire construction, all the electrodes are on the bottom layer and the top layer acts as a voltage-measuring probe. A voltage is applied across the conductive surface. Any type of probe, including fingers, gloved fingers, credit cards, pens, etc., that can be used to apply pressure against the top film will activate the screen. When ample touch pressure is applied to the top layer, the film flexes inward and makes contact with the bottom layer resulting in a voltage drop. This change in voltage is detected by the controller. By calculating the percent drop in voltage from each corner, the controller can calculate the location of the touch. Because the top conductive film layer is only acting as a probe, its physical consistency over time is less crucial than in 4- or 8-wire constructions, thus allowing a significantly higher number of actuations, i.e. 35 million touches. Dawar’s 5-wire resistive product is offered only in a Film on Glass (FG) construction.

8-WIRE RESISTIVE SCREENS (PL AND FG)

The primary difference from a 4-wire touch screen is that each edge of an 8-wire Resistive Touch Screen provides a sensing line as a stable voltage gradient for the touch screen controller. The additional 4 lines enable the controller to automatically correct for drift resulting from degraded ITO conductive coating or additional electrical resistance due to harsh environments and extended use. The extra sensing lines constantly report back to the controller the actual “baseline” voltage levels that exist in the touch area. If the baseline voltage changes over time, the controller is able to interpret the voltage change sensed during a touch event as a percentage of the baseline, thus eliminating drift and the need for field calibration. The 8-wire Resistive Touch Screen consists of a conductive bottom layer of either glass or film and a conductive top film layer, separated by extremely small, transparent spacer dots. A voltage is applied across the conductive surface. Any type of probe, including fingers, gloved fingers, credit cards, pens, etc., that can be used to apply pressure against the top film will activate the screen. When ample touch pressure is applied to the top layer, the film flexes inward and makes contact with the bottom layer resulting in a voltage drop. This change in voltage is detected by the controller. As defined above, the voltage change is interpreted in relation to the baseline voltage as sensed by the additional 4 wires. By alternating the voltage signal between the top layer and the bottom layer, the X and Y coordinates of the user’s touch are computed. In a Film on Glass (FG) construction, the bottom layer is an ITO coated glass. In a Polyester Laminated (PL) or film-film-glass construction, the bottom conductive layer is polyester. An additional layer of Optically Clear Adhesive (OCA) bonds the bottom polyester layer to a backer typically made of glass or poly material.

SURFACE CAPACITIVE SCREENS

Dawar’s Surface Capacitive Touch Screens are an all-glass construction with greater than 9H Surface hardness able to withstand over 300 million touches. A transparent conductive ITO coating is evenly distributed over both sides of a glass substrate. An electrode pattern is precisely printed around the perimeter of the glass to accurately generate an alternating current over the top conductive layer. The touch of a conductive probe draws the current to the specific point of contact. The controller then calculates the location of the touch by evaluating the flow of current from each corner. This flow of current is proportional to the distance to the touch. The ITO coating on the back of the glass functions as a shield to protect against ESD and outside interference. With no mechanical movement and a 9H surface hardcoat, a capacitive touch screen can withstand 300 million touches.

PROJECTED CAPACITIVE SCREENS

 

Dawar’s new Projected Capacitive Touch Screens consist of two ITO/Glass circuits and an Optically Clear Adhesive (OCA) that is used to optically bond the two circuits together.  A decorative lens can be added to the front surface of the sensor to allow for product designs similar to tablet PCs.  This lens is also optically bonded to the sensor layers to achieve high light transmission and low reflectance.  A touch event occurs when a finger or conductive stylus interferes with the electric field projected above the surface. This change in capacitance is detected by the controller which interprets the X and Y coordinates of the event.  Multiple fingers can be tracked simultaneously and the controller supports common multi-touch gestures.

MATRIX SCREENS

Matrix Touch Screens provide touch screen flexibility with membrane switch simplicity. Similar to resistive designs, they consist of an ITO-coated top layer and bottom layers. The layers are separated by some of the industry’s smallest spacer dots. The ITO coating is applied or etched to form rows on one layer and columns on the other. When an area is touched, the conductive coating on the top layer completes an electrical contact against the coating on the bottom layer, similar to a standard switch. These touch areas can be custom-designed to meet specific layout requirements. For additional information on how a Matrix screen may fit your specific application, please contact Dawar directly.


There are three types of touch screen technology:

• Resistive: A resistive touch screen panel is coated with a thin metallic electrically conductive and resistive layer that causes a change in the electrical current which is registered as a touch event and sent to the controller for processing. Resistive touch screen panels are generally more affordable but offer only 75% clarity and the layer can be damaged by sharp objects. Resistive touch screen panels are not affected by outside elements such as dust or water.



• Surface wave: Surface wave technology uses ultrasonic waves that pass over the touch screen panel. When the panel is touched, a portion of the wave is absorbed. This change in the ultrasonic waves registers the position of the touch event and sends this information to the controller for processing. Surface wave touch screen panels are the most advanced of the three types, but they can be damaged by outside elements.



• Capacitive: A capacitive touch screen panel is coated with a material that stores electrical charges. When the panel is touched, a small amount of charge is drawn to the point of contact. Circuits located at each corner of the panel measure the charge and send the information to the controller for processing. Capacitive touch screen panels must be touched with a finger unlike resistive and surface wave panels that can use fingers and stylus. Capacitive touch screens are not affected by outside elements and have high clarity.