In the modern world of operation terminals, controllers and remote control panels, it is no longer possible to imagine life without touchscreens. Machines show the user the information they need via the display unit (e.g. the TFT). The user can react intuitively to the information displayed and, for example, change process parameters via a touchscreen mounted in front of the display. Control buttons, sliders, rotary switches and also modern graphic concepts based on multi-touch technology are realisable with suitable software. Touchscreens are offered with various different technologies. The following touch types are established in the market:
- Capacitive (surface capacitive and projected capacitive)
- SAW (Surface Acoustic Wave)
- Infrared (IR)
The proper selection of a specific touch technology depends strongly on the requirements and the ambient conditions. We offer you all current technologies in a large number of screen sizes.
Resistive touchscreens consist of two ITO (indium-tin oxide) layers. If the surface is touched at a particular location, this creates a contact between the two ITO layers. The used controller calculates the X and Y co-ordinates touched at the contact position. Resistive technology is technically mature, can be operated in many ways (by finger, pen, medical glove, work gloves...), is available at low cost and very often most suitable for the application case. Various finishes (optical films, decorative films, front glass layer, EMI mesh to block out stray radiation, etc.) are available.
This touch technology got accepted by the market just recently due to modern mobile phones and tablets – even it has already existed for many years. The functional principle is based on an arrangement of capacitors which are distributed across an active surface in X and Y directions. In a non-operated state, each of the capacitors has a known property. The operating element (finger, special pen) invades the capacitor’s field as a disturbance and changes its capacity. The connected touch controller detects the change of the related capacitor(s) and provides the appropriate operating position. A high resolution of the detected position is possible through the interpolation of a number of these capacitors. Since the electric field of the capacitor can penetrate suitable materials (e.g. glass), decorative glass can be applied to the front of the sensor. These cover glasses, which can be printed on and of various shapes, materials and optical performances, combine attractive and functional design with scratch and impact resistance. The projected capacitive technology is now very popular and combines several benefits and a high degree of user comfort; however, the integration of such technology requires good and professional design-in to achieve best usability and user acceptance.
maXTouch™ Controller from ATMEL®
Using the maXTouch™ controllers of ATMEL®, GE Star has developed a genuine projected touch screen and also their own production process for the GE Star Touch. Just a few items of key data:
- Innovative, genuine projected capacitive multi-touch screen (up to 10 fingers)
- Works through glass thicknesses of up to 1 cm
- Extremely fast reaction time < 10 ms
- Easily operated whilst wearing gloves and suitable for medical applications
- Extremely low energy consumption (<4 watts in operation, < 13 μ watts)
- Outstanding EMC properties (30V/m) and therefore suitable for both industry and railway applications
- The active surface can be designed larger than the TFT surface, for example for operating panels outside of the display
The base of a surface-capacitive touchscreen is a glass plate coated with conductive ITO. If a position on this surface is touched by an earthed object, a charge transfer occurs and a current flow is generated. The precise touch position can be calculated by observing the respective current flows. The advantages of this capacitive touch are, for example, high optical transparency, longevity, good resolution and a robust consistency.
SAW (Surface Acoustic Wave)
SAW stands for Surface Acoustic Wave. This kind of touch screen consists of a glass plate, at the corners of which piezoelectric receivers and transmitters are fitted. Ultrasonic waves are introduced into the glass by the transmitters. The receivers compare the values received with digitally stored references. Part of the surface wave is absorbed once the surface of the touch screen is touched. Precise co-ordinates can be calculated due to the change in the sound amplitude and the runtime of this event to occur. The advantages of SAW touch are: High optical transparency, high resolution, longevity and suitability for robust deployment.
The infrared (IR) technology is based on the interruption of a light pattern in front of the screen. The touch frame contains IR diodes on two sides and photo transistors on the opposing sides. A light pattern is thus formed which is invisible to the human eye. If the light pattern is interrupted at any point, the photo transistors detect the absence of light and transmit the x and y co-ordinates. The IR touch stands out for high optical transparency, good resolution, a high degree of user comfort and longevity.