Comprehensive overview of professional touch technologies
Whether at home on your mobile phone, on the road at the ticket machine or on the tablet at work – nowadays touch-based input devices can be found everywhere. Flip charts, whiteboards and the like are increasingly being replaced by touchable displays. But behind the seemingly simple touch of a screen are many complex technologies. Even within the known input types like finger and pen, different methods already exist. In order for the touch displays to be used effectively, it is important that the appropriate technology is selected depending on the location and area of application. In this blog entry we therefore show you the different types of touch technologies and explain their special features.
Touch-based input types
Touch-based finger input is the most commonly used touch method. This method makes it possible to implement functions with gestures (e.g. zooming and navigating) very intuitively. Either the electrical conductivity of the fingers or the interruption of light beams is used to detect the positions. Depending on the touch technology, systems can be single-touch or multi-touch capable.
Pencils are mainly used for writing and drawing. A distinction is made between passive and active pens. Passive pens are recognized by their diameter and cannot be distinguished from each other by the touch system. Therefore, it is not possible to assign different functions to different pens. Active pens can be navigated with their built-in coil or by pressure detection and uniquely identified by the system. The different functions and buttons for each pen can be precisely assigned here.
Some touch systems can also detect objects by diameter, distance or code pattern. Code patterns are attached to the underside of the objects. By recognizing the objects, other systems can react to them and adapt the content in almost real time. Depending on the touch technology, the number of recognizable objects changes.
Resistive touch systems
Resistive touch systems consist of two electrically conductive layers and react to pressure. The X and Y coordinates of the touch point can be determined by measuring the voltage. Touch displays can be operated with pens and fingers as well as gloves using this technology. Today, resistive touch systems are mainly used in industry to control industrial plants and POS systems.
Capacitive touch systems
With capacitive touch systems, a distinction is made between surface capacitive systems and projected capacitive systems.
In surface capacitive systems, the glass surface is coated with a thin, conductive metal oxide coating and applied to an AC voltage. By touching the layer, the position of the finger can be determined via the measured current flow at the corners. An advantage of the surface capacitive systems is the relatively high reaction speed and the high input accuracy. In addition, the touch technology is largely vandal-proof and works even with minor scratches on the glass surface. Since no protective screen can be fitted in front of it, the system is not suitable for humid environments. Furthermore, only a single touch point can be detected.
Projected capacitive systems are often abbreviated as PCAP or PCT (Projected Capacitive Touch). These systems use two separate layers with intersecting conductors. If a finger or an active (capacitive) pen approaches, the voltage between the two fields is changed and the X and Y coordinates can be determined. No electronics are accommodated on the surface. This makes the systems very robust and a protective screen up to 8 mm thick can be attached without restricting operation. This protects the touch monitor from vandalism, varying temperatures, scratches, detergents and liquids. Displays with a projected capacitive system are also easy to clean as the entire touch monitor can be installed behind a flat user interface. In addition, the touch function can also be operated with gloves and the displays are multi-touch capable.
The infrared touch is used for large-area displays such as inexpensive large-format displays or interactive seamless display walls. Many small infrared barriers are installed in a frame, which can be interrupted by pens, fingers or objects. These infrared barriers are located just above the actual surface, so no direct contact with the touch display is required. The touch screen can also be installed behind a protective glass, which gives it a high degree of robustness. A disadvantage of the technology is that the infrared touch can be triggered unintentionally by environmental influences, such as insects or snow in the outdoor area. Furthermore, this technology does not support HID, so a driver must be installed. Shadow-Sense from the manufacturer Baanto is a further development of infrared technology and offers the advantages that touch technology is insensitive to sunlight and can detect unwanted touches at an early stage.
With the InGlass infrared technology from the manufacturer FlatFrog, infrared light rays are reflected in the pane. When touched, these beams are disturbed and interpreted as a touch event. This works so precisely that pressure strength recognition and multi-touch are possible. The pressure reading enables additional operating options such as zooming with a finger. The finger, object and pen are distinguished by their diameter. In addition, the panel is protected by an overlying, very transparent pane. This touch technology is particularly suitable for large touch displays, interactive touch screens, composite video walls and curved displays, as it offers complete optical transparency and is wear-free.
MultiTaction’s MT Cell technology can only be found in its 55 inch Full HD seamless displays. A layer behind the panels which is equipped with cameras and infrared LEDs continuously scans the surface. This technology can therefore combine a multi-touch with an infinite number of touch points and pen and object recognition.
Inductive touch displays
Inductive input systems are used either as very precise pen input systems for displays such as the Wacom board or in combination with PCAP touch panels. These input systems can only be used with special input pens (digitizers) with integrated coil. Behind the display there is a net made of metal oxide, which sends electromagnetic waves to the pen. The coil in the pin then generates a current and sends a signal to determine the position. The pens must be active and charged regularly. Inductive input systems are hardly to be found in mobile devices any more, this type of touch technology is much more needed in professional devices in such fields as medicine, education and engineering.
Linh Nguyen, student of the bachelor programme Online Media at Hochschule Furtwangen
Immanuel Roß, AV consultant and project engineer, macom GmbH
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