I regularly have customers trust a tablet into my hands with the request ‘can I have a touch screen that works a bit like this?” What they mean is, they’d like the same quick instant response, multitouch support and recognition of gestures like pinch and zoom.
The answer (of course) is yes. Multi-touch support requires Mutual Capacitive touch technology with pairs of drive and sensing cells. Gestures like pinch and zoom are based on multitouch, and can’t be implemented on screens that only recognise one or two touches. They also need suitable software in the controller. Touch drivers will only deliver the location of a touch – additional algorithms are needed to recognise and respond to gestures. Fortunately, software modules offering this functionality are readily available for Windows and Linux systems.
Not all applications have either the budget or the need for multitouch, and single/dual touch self-capacitance technology, with just a single set of drive lines referenced to ground, is around 30% cheaper. If your system just presents the user with a series of buttons, self-capacitance technology is fine. It has other advantages too – it is less sensitive to noise and more robust.
There is another alternative: resistive touch. As per my previous blog, even though it is regarded as cheaper, truthfully the price difference between this and self-capacitive technology is now very small and the technology is less sensitive. It is also often used where gloved hands are present, but as sensitivity improves capacitive technologies can be used here too.
Both capacitive technologies work well through cover glass or lenses, allowing the system to be well protected from abuse and the environment. An area that we often help with is setting the sensitivity correctly. Increasing sensitivity can lead to false touches and susceptibility to noise – whilst decreasing it can impact performance and usability.
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