Displays & GUIs Let’s be practical about this From a manufacturer’s point of view, lowering cost and increasing reliability are strong factors, particularly when adding capacitive touch functionality to passive LCD displays. By Hussein Isik U and tablets, they might not be the most optimal solution for machines in a harsh industrial environment, or for home appliances. For instance, wireless climate control units manufactured in large volumes need a limited number of buttons, low current consumption and low cost. Technical development around touch-screens has been driven by the portable device format, but there are many other consumer and industrial applications where capacitive touch displays are desired, but adoption has been relatively slow. A key challenge in bringing capacitive touch displays to non-mobile applications is the required thickness of the overlay, the front glass. Unlike smartphones and tablets, the overlay of displays used in industrial and home automation products has to be thick enough for wear and tear in harsh environments. Figure 1 shows the model of a capacitive touch system: a metal pad is surrounded by a metal ring at a certain distance; a plastic overlay covers the metal pad and the surrounding metal ring. A touch sensing event was simulated with different Figure 1: Capacitive change obtained with a touching finger: finger-to-pad capacitance thicknesses of overlay. and pad-to-metal ring capacitance Figure 1 shows the ser interfaces based on touch screens have become a must for most applications in our daily lives, whether they are for infotainment systems, equipment for personal health care, home appliances or point-of-sale machines. Influenced by smartphones and tablets, users are looking for an improved experience with their coffee machines, refrigerators, climate control units and many other devices. Depending on the application, the requirements for the display and the touch function can vary significantly both from the cost and technology point of view. Although TFT displays with advanced capacitive touch functionality are dominating in smartphones 42 | November 2013 | Electronic Specifier Design