TOUCH SCREEN IN EDGE DEVICE

Touch screen in the edge device

95%+ designs customer is selecting touch screen in their display designs. The chosen touch technology is 98% of the cases PCAP (projective capacitive display). Very few are selecting something else like example resistive touch screen or infrared touch screen. That is quite clear so far and is driven by the fact that most displays are acting as HMI/UI (Human Machine Interface/User Interface). The driver for this has been smartphones with Apple as the first adopter. Much of the user experience is created by the touch screen and that is why it is vital that it is working properly. Big part of the UI -design is as well defined with the touch screen functionality. People are having different size of fingers, people might use gloves, there can be different fluids on the touch screens. There are lot of environmental issues as well like different fluids on the touch, temperature extremes, sunshine, frost, humidity etc. All these things are challenge for touch screen design and need to be addressed during design face.

Typical issues with touch screen design

When starting the touch screen design the groundwork should be done properly so that the problems are avoided in the later stage. It is much easier and cheaper to cope with the problems before the products are in production and distributed to customers globally. If in past you used to buy standard products that is no longer working. Every PCAP design in a custom project so prepare accordingly. The design is starting by carefully analyzing the environmental conditions, possibility for EMC/EMI (Electro Magnetic Conductance, Electro Magnetic Interference), durability requirements, needed optical features etc. For this you should always talk to specialist who knows the pitfalls in PCAP -design and can guide you throw possible problems. You need always first to get specification documents signed and the first prototypes to be delivered. After that you can start the actual testing and final tuning of the PCAP. Not a single PCAP is ready for usage out of the box.

Designing the touch screen

When you have selected the good partner for your touch screen design there are few things to consider. What kind of PCAP -sensor technology to choose? Most common one is ITO but that can be also build in different ways. Example one side, double side, on glass, on plastics etc. It can also already be on the display cell or in the display cell. You could also consider using mesh technology for the touch or nano tube style. So, there are plenty of options to consider. Top of the touch screen you maybe need different kind of filters like UV-Filters, polarizer filters, O-ring filters etc. This is affecting the robustness of the design and its ability to create good user experience. The other important topic is the touch & cover lens & display bonding. It is giving the final optical & durability features to the touch stack. Cover lens is always finally the part which is visible and is usually presenting the brand image of the company. Including sometimes filters, company colors, logo’s led hole’s etc. Cover lens is always designed in co-operation with the industrial designer who is giving brand look and feel to the device.

What was forgotten from previous?

Maybe the most important part of the touch design = Touch controller. Controller selection is very important and is going to make the difference in the performance in different conditions, longevity, EMC/EMI, sensitivity, user experience. There are handful of controller vendors who can provide good controllers with industrial features. These vendors are EETI, SiS, Ilitek and Microchip. In the market you can find many more vendors as well with variety of features & capabilities. But it is wise to choose from the vendors which are really having industrial feature set supporting the difficult conditions. Top of the controller vendor you should select supplier who is able to support you during the project as well after sales in case there are problems arising. No controller is good unless you have perfect vendor who can support you with controller tuning & possible other issues. In these controllers there are several hundred parameters which can be tuned and learning how to tune and touch controller can be very tricky and not necessarily possible at all when support is missing. Controller also need to be installed on either in separate PCB (Printed Circuit Board) or attached to the interface foil.

Sleep your nights well and be happy

When you have selected right vendor, you can be worry free as you will your project supported throw out the life cycle of the product. You will get right product for your application which will give the best possible user experience for your product. Supply chain issues are taken care and products will be delivered in time for your production. If you make a mistake with vendor selection it can become costly and painful experience. My advice is that use your time in the design face to make sure that everything is as it should be. That will pay of end of the day.