By Ian Crosby, Sales and Marketing Director, Zytronic

Touchscreens are becoming the preferred basis for user interfaces in all manner of applications, including consumer goods, digital signage, factory automation, information kiosks and medical diagnostic equipment. Developments in touch technology not only broaden the scope of where touchscreens can be deployed, but also provide a route to delivering new and innovative touch-based applications such as ‘smart mirrors’.

The well documented benefits of touch control mean that touchscreen-based designs are now part of our everyday lives, whether at home, in the office or in the vehicles we use to travel between the two. Indeed, touch control has become key to the user experience and the foundation on which designers can build an ever increasing variety of new and emerging innovative applications. This type of innovation is well illustrated by considering the introduction of touch interfaces into mirrors.

Several television manufacturers have already combined optically coated glass front panels with LCD displays to create low profile wall-mounted TVs that can switch between video and reflective surface mirror modes. The reflective/transmissive properties of the coating allow the glass to appear transparent when the display situated behind it is illuminated, or reflect light when the display is unlit. These TVs deliver high definition video entertainment when in operation and become decorative items when turned off.

The next logical step is to not only integrate displays into mirrors but to add touchscreen functionality to create interactive ‘smart mirrors’. Such mirrors could, for example, allow business executives to check that morning’s opening stock prices while shaving or brushing their teeth. Via the touchscreen the user might be able to browse web pages in order to read news headlines or sports results, or to control the view from a webcam that allows them to check their appearance from different angles during grooming. Fitting rooms in clothing stores could install smart mirrors capable of calling up images of matching accessories or allowing customers to check if other sizes/colours are in stock.

What’s more, because mirrored displays are more aesthetically pleasing than standard displays when turned off there is even the possibility of delivering benefits in terms of curbing electricity consumption/environmental impact. No longer would displays need to be kept in constant use (for instance in shop front displays outside opening hours). Use of this technology could also help to make electronic equipment inconspicuous, for instance in building automation control panels or security alarm systems.

Design objectives
As with any modern touch-based design, smart mirrors will require touch solutions that deliver high-accuracy, high-speed responses. There could also be the need for flexibility in terms of how much of the mirror’s surface area is utilised as a screen at any stage – it may even be desirable for the chosen active area to be repositioned, as opposed to being held fast in one place. Given the settings in which these mirrors are likely to be used – for instance bathrooms or health club changing rooms where they will be exposed to water splashes and wide variations in temperature – the touch solution will need to be rugged and reliable. At the same time a long lifespan and the minimising or eliminating of costly maintenance call outs or replacements is likely to be important. It is also vital that the touch solution deployed helps to address the aesthetic design requirements – for example by optimising the quality and brightness of the image displayed on the mirror and by supporting a stylish, smooth-fronted design. The challenge, therefore, is finding a touchscreen technology that can address these various criteria.

Choice of touch technologies
Traditional front-face-active touch technologies, based on resistive or surface capacitive sensing techniques, have considerable drawbacks when it comes to meeting the
requirements outlined above. As their sensors are placed on the external surface of the glass, from the start they will have a detrimental affect the appearance of the reflective coating. However, this positioning also means that they are unavoidably exposed to the outside world – subjected over time to all manner of wear and tear. Alternative infrared (IR) or surface acoustic wave (SAW) technologies are also front-face-active in nature, and though they are based on light and sound waves still have fundamental disadvantages for touch mirror design. These technologies require their sensor elements to be situated in bezel structures around the perimeter of the active area. These bezels can make the mirror difficult to clean, and with dirt and dust likely to build up in their recesses, impair sensor operation. They also limit flexibility in terms of aesthetic considerations as well as bezels making alteration of the size or moving of the active area of the display to other positions more difficult.

It is for this reason that designers of smart mirrors are more likely to turn to solutions such as projected capacitive touch technology. This has become increasingly popular within the portable electronics sector in recent years, playing an integral part in the success of products such as the Apple iPod Touch and iPhone. Projected capacitive satisfies all the criteria previously outlined, however, this type of technology can usually be applied to small display formats. This is now changing as proprietary touchscreen technology developed by Zytronic can now bring projected capacitive sensing to large size displays, up to 100-inches.

Zytronic’s patented Projected Capacitive Technology (PCTTM) sensor technology comprises an array of micro-fine copper conductive tracks, in an XY grid arrangement, which is embedded into a laminated substrate. When the user’s finger approaches the front surface of the sensor, a change in capacitance is detected at the corresponding position on the grid. The coordinates are then fed back to the controlling computer. The substrate can be placed behind an overlay of glass or polycarbonate that can be as thick as 20mm thick, protecting it from accidental and malicious damage as well as the effects of moisture, liquids, chemicals and heat. What’s more, as the sensor elements are only 10μm in diameter they are effectively invisible to the human eye, so they do not impinge on the appearance of the display, either when it is lit or when acting as a mirror.

PCT design considerations
Projected capacitive sensing in mirrored glass applications depends upon the reflective/transmissive coating being non-conductive. Since the sensor array is positioned
behind a glass overlay it must be able to detect the electrical effect of the user’s finger close to the glass surface – the presence of a conductive coating could prevent this. Although, mirrored glass previously required depositing of a thin metallic layer, modern nonconductive coating materials are now available which circumvent this issue.

Smart mirrors in action
A project to develop an interactive mirror product was recently embarked upon by Zytronic and Taiwanese user interface specialist Sunvision Technology. A 15.6-inch custom version of Zytronic’s PCT-based ZYBRID® touch sensor formed the touchscreen of Sunvision’s ViViMirror. By employing PCT-based sensing it was possible to localise the touch capabilities in the region of the display, without the need to employ an unattractive bezel. This provided the flexibility to create interactive mirrors in a wide range of sizes, presenting a completely smooth front surface even when the display/touchscreen assembly occupied only part of the mirror’s total area. The field generated by the PCT sensor matrix is sensitive enough to be fully responsive through the 3mm non-conductive, optically coated glass overlay.

The ZYBRID sensor permitted precise and highly responsive touchscreen functionality while retaining the full reflective/transparent properties of its specially selected two-way glass. ViViMirror conceals the touch-enabled TFT-LCD display until such time as it is required. It is also possible to have facial, fingerprint or RFID based recognition mechanisms integrated into the system for security purposes. ViViMirror can facilitate a wide range of tasks; the viewing of data from a personal network, adjusting of heating/ventilation settings, helping shoppers to choose what merchandise to buy, or control of alarm systems. The manufacturer envisages it seeing strong uptake in retail, leisure, domestic and interior design applications . The resilience delivered by the PCT-based touchscreen makes it suitable for fitting in bathrooms, integration into kitchen appliances, and even outdoor use.

Conclusion
Touch sensor technologies have moved beyond the front-face-active display overlays of the past, towards fully integrated and embedded interfaces which employ non-contact control methods. By making robust and reliable two-way interaction possible in a variety of challenging environments, solutions such as projective capacitive technology hold the key to delivering commercially viable smart mirrors as well as a host of other innovative, touchbased products, irrespective of display size and location.