Digital display technologies give new options Saint Paul MN

Liquid crystal display relies on fluid display formats

LCD devices are available in two fluid display formats: 1) segment system — a simplistic design in which the display unit is composed of a series of separate figure eight loops, each capable of displaying numbers and letters (e.g., the format typically found in alarm clocks, cell phone screens, sports scoreboards, etc.); 2) matrix system — a more complex design that incorporates a set of dot matrix components arranged in rows and columns to form numbers, letters and graphic objects. On-board vending machine video contents use a matrix system format and average 10 to 15 seconds per product advertisement.

Commonly used LCD fluids used within the formats include twisted nematics (TN), super twisted nematics (STN) and film compensated super twist nematics (FSTN). The term 'twisted' is meant to communicate the angling of molecules between alignment layers — within the LCD panel — to make screens easier to read and viewable from almost any viewing angle. TN displays are simplistic, basic digital technology that is usually reserved for inexpensive devices such as calculators, wristwatches, clocks, caller ID screens and gas pump price displays. Compared to TN technology, STN is superior in providing a platform for enhanced viewing since the screen projects a higher contrast ratio. In essence, STN screens are clearer and sharper than TN displays. STN displays are ideal for matrix system usage and can be found in portable bar code scanners, hospital equipment, PC storage devices, and related equipment, and is the preferred format for vending machine mounted screens.

Unlike STN, FSTN involves the application of fluid technology to produce a light-colored background with dark image pixels in the foreground. Although fluids with higher contrast ratios enhance viewing angles, they do so at a higher cost. FSTN could increase its market share should associated costs decrease.

Touch screen formats: resistive and capacitive

There are two formats of touch screen devices: resistive and capacitive. A resistive screen typically is constructed from a normal glass panel covered with a conductive and resistive metallic layer. The two layers are held apart by spacers and a scratch-resistant layer of clear polyester is placed on top to ensure readability.

Electricity is circulated across the layers, and the pressure of the user's touch on the screen causes the layers to make contact in a meaningful location. The coordinates of the touched spot are translated into input data.

Resistive touch screen devices are effective in low volume applications. Resistive devices tend to struggle with highly repetitive touches regardless of media used (finger, plastic card, pencil tip, or other object). Part of the problem with resistive touch screens is that over time, frequently contacted areas become much less clear, and therefore more difficult to decipher.

In an infrared capacitive system, a layer that stores an electrical charge is placed on the glass panel of the monitor. Small amounts of voltage are applied to the screen from the four corners of the device. The user's contact with the monitor causes some of the charge to be transferred to the user, thereby reducing the charge on the capacitive layer. The location of this decrease (a minute amount of electrical current to the point of contact) is measured and converted into input data. Since there is no need for a top sheet (also referred to as a cover sheet), an advantage of capacitive screens is the ability to transmit brighter and clearer content. In addition, capacitive screens are estimated to last eight times longer than resistive screens.