Users of high-tech equipment in the consumer world as well as professional sectors such as industrial, medical, military and e-commerce are becoming increasingly familiar with touchscreens and the pros and cons of various types of technologies. This brief guide describing the principles and strengths of touchscreens should help when deciding which to buy or design in.
After windows-style software, touch is the next big user-interfaces innovation making high-technology accessible to users of almost any skill level, from the high street to the factory floor. Intuitive, attractive and fun to use, a touchscreen is a must-have for products needing to be perceived as cutting edge. There are a number of ways to build a touchscreen monitor, and most use either a resistive or capacitive sensing principle. Each has a number of strengths and limitations.
Daylight readable
This is normally achieved by increasing the backlight brightness in the display. This will have an impact on battery run time.
Sunlight readable
Manufacturer’s use special filters on the screen to increase the contrast ratio. This is achieved without consuming additional power.
Capacitive touch
The capacitive touchscreen is the most widely used technology in today’s smartphones. The touch sensor, which covers the surface of the industrial display – typically an LCD or OLED – comprises two layers of glass separated by spacers and each having a coating of conductive material such as Indium-Tin Oxide (ITO) on the inner surface. The ITO may be deposited as stripes, as in the iPhone or iPad. In this case, the glass layers are arranged so that the stripes run at right angles to each other. This creates a grid of minuscule capacitors, each capable of projecting an electric field a short distance through the front glass. For this reason, this type of capacitive sensing is called projected capacitive technology.
As the user’s finger approaches the screen it disturbs the electric field producing a measurable change in the value of the capacitors local to the touch point. The touchscreen control electronics, which may be mounted on the sensor or a separate PCB, are able to determine the location of the capacitors most affected by the change, to decode the position of the touch.
With improvements in the design of the capacitor grid, and the controlling electronics and firmware, it has become possible to detect multiple static touch points as well as moving touch points; these capabilities are the basic enablers for the sophisticated multi-touch features seen in today’s smartphones. They include pinch, flick, double tap, or touch and hold. With these, users can easily perform tasks such as resizing images, scrolling through content, opening documents and navigating menus.
Resistive touch
A resistive touchscreen uses a similar construction, comprising two ITO-coated layers separated by a grid of spacers. The ITO coatings have carefully controlled resistive characteristics. The outer layer is made from a flexible material and deforms when touched. Touching therefore brings the two layers into electrical contact, producing changes in resistance. From the changes detected, the touchscreen controller is able to extract the x-y coordinates of the touch point.
Touchscreen strengths and weaknesses
Each of these touch technologies is well established and has become extremely successful. As may be expected, each has strengths and limitations. Designers must take these into account when selecting a touchscreen for their next product. End users, also, are becoming much more tech savvy and increasingly likely to consider the pros and cons of the screen in detail before making a buying decision. The internet has many discussion threads and blogs discussing the performance of touchscreens, touch technology and various touch-enabled products.
Briefly, the resistive touchscreen is a mature technology, very competitively priced and used in the majority of PDAs as well as some smartphones. A resistive touchscreen will work satisfactorily if the user is wearing gloves. However, in many applications using a stylus (usually provided) is recommended since the flexible screen is easily damaged by fingernails or if a sharp object such as the tip of a pen or a key is used. When used with a stylus, resistive touchscreens offer very high accuracy. This accuracy, combined with low cost, is a key strength of resistive touchscreen technology.
Projected capacitive technology is today’s favourite in smartphones and tablet PCs, as well as other computing applications such as panel PCs embedded in industrial control units, security systems, medical equipment, kiosks and interactive signage. With no need for a flexible front panel capacitive touchscreens tend to be physically tough and durable. They can be sealed to a high IP rating such as IP65, and are easy to integrate into equipment for use outdoors or that must offer wipe-clean convenience for the sake of hygiene or appearance. Examples include IT equipment used in food production or customer-facing devices such as interactive signage or store maps, e-commerce terminals and ticketing equipment.
Capacitive touchscreens are also sometimes described as "finger friendly". No stylus is needed, hence offering greater convenience. This can be particularly important for portable products, where one-handed operation may be desirable. On the other hand, a capacitive touchscreen is unable to detect touch using a stylus for extra accuracy, since it is dependent on the change in electric field created by the path to ground presented by the user’s finger. A fingertip is generally considered a less accurate pointing device.
Selection of the best touchscreen technology can be a case of choosing the right horse for the right course, or in some cases may simply come down to individual preference. By and large, buyers of consumer devices must accept the selection offered by their preferred brand.
Getting it right
However, touchscreens are becoming relied on increasingly to add value to medical, industrial, financial, military and other types of equipment. for these applications, designers can base their selection on carefully considered criteria such as ruggedness, sealing or cleaning requirements, screen sizes available, and of course cost.
A growing proportion of today’s workers are from the iPod generation and, as such, expect a flawless user experience when interacting with technology at home, on the move or at work. Hence it is increasingly important for designers of professional equipment to provide touch features in their designs and to use the right touch technologies in the right places.