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Display Technology


Higher drive for touch controllers transforms the industrial user interface


Human Machine Interfaces (HMI’s) used in hazardous or industrial applications have a difficult life, and their designers face many challenges when integrating interactive technologies into these systems. A new generation of touch controllers will transform the design of industrial projected capacitive (PCAP) touchscreens, with technical innovations that deliver better performance and functionality than ever before. Specifically, a much higher drive voltage brings improved tolerance of unfavourable conditions. Ian Crosby, sales and marketing director, Zytronic explains


T Improved noise immunity


he biggest constraint on PCAP touchscreen performance is noise immunity. When the touch controller


receives a signal from the sensor, it must distinguish between genuine and false touches (created by electromagnetic interference, or EMI). A finger pressed firmly onto the screen will give a clear signal – but that signal will be weaker if the user is wearing gloves, touching lightly, or the screen is behind thick cover


glass, and/or the surface is contaminated. The key to improving sensitivity is the drive signal applied to the sensors Transmit (Tx) array of electrodes by the touch controller. The level of this signal is a classic trade-off, a low voltage signal can be overwhelmed by EMI from the environment, a high drive voltage can create interference in the sensor itself which can potentially degrade performance.


Most PCAP touchscreen manufacturers are forced to use a Tx signal with a DC


current of between 20-30V, due to limitations in available “off-the-shelf” touch control components and ASICs. However, Zytronic’s new ZXY500 range of controllers have been purpose designed to operate at an industry leading Tx drive voltage of up to 40V, enabling full multi- touch detection in extremely challenging industrial applications. The result of this innovation is dramatic. The higher drive voltages reduce the influence of noise on the data captured. With all PCAP touchscreens, it is necessary to have a gap (air or resin filled) between the front of the display and the rear of the touch sensor, and the new ZXY500 controller now allows this gap to be substantially reduced, depending on the size and type of display selected for the system.


Touchscreen design In addition to directly improving performance, this new generation of ZXY500 touch controllers combined with Zytronic’s flexible PCAP manufacturing process, provides system designers with limitless opportunities to customise the appearance of the user interface irrespective of quantity, optimising it for the application and helping to differentiate the overall hardware from competitive products. The new controllers allow the border


around the perimeter of the touch active areas of the screen to be substantially reduced (Figure 1) – for example a touch sensor designed for a 55” display can now be designed with sub 10mm borders, helping to reduce the user interface ‘footprint’. Zytronic has been able to achieve this


Figure 1: Zytronic’s new controllers allow the border around the perimeter of the touch active areas of the screen to be substantially reduced


border reduction through proprietary new touch detection algorithms in firmware which allow the transmit and receive electrodes in the sensor borders to be located far closer together without creating interference or “cross-talk”. The ZXY500 controllers also now make it possible to design “soft” keys around the edge of the dynamic active area of the projected capacitive touchscreen. These fixed touch “buttons” are managed by the same controller and their function can be defined by the system designer. This is useful in applications where sealing and water ingress via mechanical controls could be an issue.


Figure 2: The proprietary ASIC within the Zytronic ZXY500 controllers also increases the speed of touch detection, updating touch co- ordinates in just 1ms at the controller output


The new PCAP controllers support up to 80 simultaneous touches, enabling true multi-user interactivity and improved “palm” rejection capability. The Zytronic proprietary ASIC (Figure 2) within the ZXY500 controllers also increases the speed of touch detection, updating touch co-ordinates in just 1ms at the controller output – reducing touch latency by a third compared to the previous generation controllers, and improving the overall user experience. They can also reliably detect touches through more than 8mm of overlaying glass – even with gloved hands, and are unaffected by rain, salt water, oil or ice on the surface of the touch sensor.


Tactile feedback ZXY500 PCAP touch controllers use “force” sensing to overcome the issue of touchscreens not providing tactile feedback. Zytronic has developed custom touch detection firmware which responds to the increased surface area of a fingertip when pressed more firmly onto the screen and differentiates its output accordingly. Software developers can then use the graduated information from the controller to activate different functions depending on the applied pressure, such as issuing an audible message alerting the user to the option selected when the screen is touched lightly, and then confirming the choice when pressed harder.


www.zytronic.co.uk


www.cieonline.co.uk


Components in Electronics


September 2018 15


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