Passengers and staff increasingly rely on information about journeys, networks and other facilities to ease circulation around the transport system. A reliable supplier which also offers design support can elevate display technology for all users and meet the needs of a connected transport system.
There are many display and touch screen choices available, each with its own features and characteristics.
Relec Electronics offers a range of Thin Film Transistor LCD (TFT) displays, with or without integrated touch screens, from 1.77 to 31.5 inches in size. Rather than a standard display, the specialist engineering company is able to tailor a solution for the required environment, whether inside a driver’s cab, on shielded platforms for passenger information, or in exterior locations where they are subject to extremes of temperatures but also subject to heavy use (for example ticket machines).
TFT displays can be constructed from a number of different technologies, but today’s market is dominated by two, TN (Twisted Nematic) and IPS (In-Plane Switching).
TN technology has been around for many years, with displays available in a wide variety of standard sizes. TN displays are generally cost effective, have fast pixel response times and consume little power, but they suffer from poor colour reproduction, low contrast ratios and limited viewing angles.
IPS technology has solved many of these problems, providing virtually 180° viewing angles. IPS technology arranges and switches the alignment of the crystal molecules between the glass substrates, which reduces the amount of light scattered in the matrix and also results in higher contrast ratios and improved colour reproduction.
Reduced glare and improved strength
TFTs are susceptible to glare and reflection from either bright light or direct sunlight, making it difficult for a viewer to see the information clearly. Clear visibility is particularly important in instrumentation in the driver’s cab but is also desirable in passenger information systems. Glare and reflection can be dramatically reduced by the addition of an optical bonding layer.
Optical bonding introduces an optical compound, usually a gel, between the cover glass and the TFT. This layer helps to minimise trapped moisture and reduces the effects of fog in the display, to ensure a clear view. By reducing the internal reflection, the display’s contrast is increased and the screen is more visible in bright conditions, without the need to increase the brightness levels, which would increase power consumption.
The process also enhances the strength and durability of displays, which may be located in high-thoroughfare areas, such as ticket halls. It prevents condensation and the ingress of contaminants, which can threaten the display’s operation. The process improves resistance to vibration and moisture, adding to its reliability and also optimises its performance in harsh temperature environments.
Displays can be further strengthened by the addition of a toughened cover glass, up to nine millimetres thick, to further increase durability and vandal resistance. This feature is particularly useful in ticket machines and public areas, and where downtime due to damage and repair needs to be kept to a minimum.
Another option available to display integrators is fitting anti-reflective (AR) or quarter-wave polarisers. An AR polariser is a clear film that is applied to the panel to reduce the amount of reflection created by bright external light.
In a typical TFT display, there are three layers through which light passes, namely the cover lens, an air gap, (which can be optionally filled using an optical compound) and the TFT panel. Within each of these, there is a reflection of approximately five per cent under direct light, making a total of 15 per cent reflection.
The AR polariser reduces this to approximately nine per cent. Up to three layers can be applied to a single display to further reduce the reflection. For example, using two layers reduces the reflection to five per cent and, with three layers, the reflection is reduced even further, to just 0.5 per cent.
AR polarisers can be applied to the top or bottom of the cover glass, or to both to further reduce reflection. However, if the display has a projective capacitive touch panel (PCAP), the AR polariser can only be applied to the top of the cover glass due to the sensor film.
There are also quarter-wave polarisers. These are designed to improve the viewing of TFT displays when wearing polarised lens sunglasses. TFT displays naturally output light in a single plane – if this is 90° out of sync with the viewer’s sunglasses, the display can be practically unreadable, appearing virtually black.
Relec Electronics has been working closely with partners to develop quarter-wave retarder films which resolve this particular obstacle to viewing TFT displays.
Touch panel optimisation
The company also has high-noise-immunity touch-panel options, with models providing up to 32V/m noise immunity to ensure that exterior signals do not interfere with the display. This is particularly relevant for mission-critical displays in driver’s cabs or central control systems. High-noise-immunity touch panels are also specified for use in medical, automotive and avionics equipment and systems.
To meet an application’s requirements, the touch-screen firmware can be tailored to the user’s specifications via a Graphical User Interface (GUI). In this way, a number of features can be defined, including, for example, the number of touch points. This is useful to reduce the fixed number of points on the original firmware or it can be used to increase the number, to allow for more gestures.
The GUI can also be used to determine touch sensitivity for optimal performance. If the current level is too sensitive, it can produce ‘ghost’ touches, or the screen might be susceptible to a noisy environment. If, however, the installation is located behind a second piece of glass, the sensitivity needs to be increased, to maintain the level of performance.
The firmware can also be tailored to meet the installation mounting type (landscape, portrait, 180°) by rotating the axis of the display.
The input method is also implemented via firmware, for example, the click mode can be adjusted to either emulate a mouse or standard touch mode.