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A Touchy Subject

A Brief Exploration of Touch Screen Technology

Touch screen being activatedThe chances are extremely good that you have come into contact with a touch screen in the last twenty-four hours. If you’ve visited an ATM, paid for groceries with a credit or debit card, or even rented videos from those ubiquitous “boxes” springing up everywhere, you have met the touch screen. You’re probably aware of the fact that not all touch screens are created equal. I can’t tell you how many times I’ve stood there stabbing the screen with my finger for ‘debit’ until the cashier kindly instructs me to use the stylus. I’ve often wondered, “How do you know when it’s safe to give it the finger?”

So what are touch screens, anyway? Though not complicated, the answer involves a bit of explanation. It is important to note that there are actually several different types of touch screen technologies. Each one has its own advantages and disadvantages, which makes them suitable for different purposes and environments. If you’re in the market for a ruggedized touch screen LCD monitor, you may find this information invaluable in helping you decide which touch screen technology will aid you in your specific application.

The first type of touch technology that we will explore is called a Resistive Touch Screen. In this technology, the touch sensors (collectively referred to as the touch screen) is composed of two relatively transparent metallic coated layers: a conductive layer and a resistive layer. When the system on which you are working is operating, an electric current runs through both of the layers. When pressure is applied to the screen, the two layers touch in the exact spot that is being pressed. It is this pressure that creates a change in the electrical field. The other component of a touch screen, the touch controller circuit board, detects this change in the electrical field and translates it to the computer as a click—or drag, like a mouse—to bring about the desired results.

Resistive touch screens respond to pressure applied to the screen. It is this technology that works with a finger, a gloved hand, or even a pen point. That makes it advantageous in many applications. That translates into greater flexibility in use. The disadvantage to this type of touch screen is that while writing on the screen your palm cannot rest on the screen. Your resting palm would create pressure on the screen causing the computer to detect another spot on the screen, which disrupts the activity.

Resistive touch screen diagram

The Key Components of a Resistive Touch Screen

1. Polyester Film

2. Upper Resistive Circuit Layer

3. Conductive ITO (Transparent Metal Coating)

4. Lower Resistive Circuit Layer

5. Insulating Pads

6. Glass/Acrylic Substrate

7. A touch of the overlay surface will cause the Upper Resistive Circuit Layer (2) to contact the Lower Resistive Circuit Layer (4), producing a circuit switch from the activated area.

8. The touch screen controller receives the alternating voltages between the two circuit layers (7) and converts them into the digital X and Y coordinates of the activated area.

Another type of touch technology is a Capacitive Touch Screen. A capacitive touch sensor consists of a sheet of glass layered with a relatively transparent metallic material that stores a small electrical charge. We, too, as humans, carry an electrical charge. When our finger comes into contact with the glass, our electrical charge meets the charge of the glass. In effect, we create a decrease in the charge of the glass. The computer detects this drop in charge through sensors located in each corner of the glass. The touch controller then performs a series of calculations to determine the precise location at which the glass was touched and also translates it to the computer as a click (or drag) like a mouse.

Capacitive Touch Screen

Capacitive Touch Screen

Because capacitive touch sensors do not rely on pressure applied to the screen, they can be used in far more discriminatory environments. One of their greatest advantages is that capacitive touch screens are highly accurate. Capacitive technology works well on cell phones because they respond to the touch of a bare finger; a stylus or similar device will not work because it is not conductive. Throwing a cell phone into a pocket no longer carries the attendant woes of dialing a melon peddler in Malaysia by happenstance. Capacitive technology is best suited for indoor applications. An exposed electric charge severely limits its use in areas open to weather.

Other types of touch capability are infrared touch screens and surface acoustic wave touch panels. These technologies are not as common in the consumer marketplace. Like capacitive technology, both infrared and surface acoustic wave touch screens rely on electron fields to detect stimuli (interruptions in the field by fingers or stylus) and take the appropriate actions via touch controller. Whereas infrared touch screens form a grid of infrared light on the screen, surface acoustic wave touch panels use ultrasonic waves to produce a grid. Both infrared and surface acoustic wave touch screens work well with a finger, gloved hand, or other stylus.

Here at General Digital, we can integrate any of these technologies into many of the monitors that we produce. In addition to the technologies listed above, we also can integrate projected capacitive, optical, and Dispersive Signal Touch (DST) technologies into our ruggedized LCD monitors. This is by no means designed to be an exhaustive explanation of touch sensor technology. More information is available to aid you in your choice of touch screen technologies on our web site at http://www.generaldigital.com/touch-screens-for-lcd-monitors.

© General Digital Corporation
© General Digital Corporation

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