Increasing sophistication in displays & touchscreens

Once a touchscreen was a novelty, then it became an expensive but sometimes useful extra, and then along came the iPod and the world changed. Now, there is an expectation for touchscreens among many users that would not have previously considered them, but despite the technology’s widespread adoption it still comes at a price in terms of development time. Touchscreens also bring extra requirements such as more brightness and thus higher power consumption. The result was that touchscreen technology needed to change, and it is changing and improving. On top of that, there is a general demand in displays for higher contrast and wider viewing angles.

“Now, everyone wants a touchscreen on their products,” said Paul Hooper, Worldwide Displays Sales Manager, Anders Electronics. “People are familiar with using touchscreens. It also means they can have bigger screens on their products because you don’t need the buttons.” The traditional form of touchscreen technology was resistive, with a single touch. But capacitive touch technology, allowing multiple touch, is becoming more popular as people become used to using it on their smartphones and tablets.

There is, though, a penalty to pay. Hooper estimates that with resistive, 90% of the design work is mechanical with only 10% electronics and software. This switches dramatically with capacitive, with only 40% mechanical and 60% electrical and firmware. Even though there are drivers for touchscreens in some of the operating systems, they still need to be tuned into the particular product. “It is a big difference,” he said. “You have to tune the touchscreen to your product. We have our own firmware engineers to help with that, but a lot of this is expensive. You can get some that are plug-and-play, but more often than not they need tweaking.”

Some manufacturers are looking at implementing capacitive touchscreens ‘in advance’, so the users do not have to worry. “That should make it easier for the customer,” said David Potts, Divisional Marketing Manager, Anglia. “That is in development at manufacturers at the moment and is one to watch out for. It will come into the consumer market first and then into industrial.” This, he believes, should increase capacitive sensing use in industrial where the product manufacturers do not have the same resources and capabilities as the smartphone and tablet makers, adding: “It’s not a cheap process so it is not being done at the moment.” One of the limitations with capacitive sensing has always been the use of gloves because they need the capacitance from the user’s fingers, but these days the sensitivity has improved so they will work with medical gloves and some with even thicker gloves.

“We have also got it to work through Perspex,” said Hooper. “The sensitivity is improving. You have to adjust the firmware to do this.” A lot of existing displays use twisted nematic technology, and that is still popular, but there is a move towards In-Plane Switching (IPS), which gives a wider viewing angle but has struggled with contrast, though recent version have improved on that. “IPS has been around a few years and was in the first IPad 2, and now it is coming into industrial applications as well,” said Hooper. “But it is more expensive and for certain applications it is not necessary.”

As well as reducing the brightness, adding touchscreen technology can also cause difficulties with reflections, especially outdoors; this has led to a lot more work with optical bonding. This used to be expensive because of yield problems, but manufacturing techniques are improving and the cost is coming down. There is still a demand, however, especially in the industrial and medical fields for more basic screens, even monochrome.

“Some of these applications don’t need the leading edge,” said Hooper. “I can’t see OLED being used in industrial in the short term. It is superior, but there are limitations for industrial applications, such as its lifetime. And although we see a lot more using colour, there is still a lot of demand for monochrome in industrial. Driving a colour display is more expensive and in some applications this is enough to sway them towards monochrome. Some handheld devices in medical still use monochrome.”

But Potts believes that as high-resolution panels become cheaper there will be less demand for the older styles: “The industrial market is still using much lower resolution panels,” he said. “But I think they will be forced to move up in resolution as things move on. The trend in panels is starting to get bigger, so the availability of smaller ones will become harder because the volumes will not be there.” This is also leading to a change in the interface, said Potts: “In industrial, most TFTs have CMOS or LVDS interfaces, which are fine for low resolution, but as resolution goes up, you are seeing more of embedded Displayport and Mipi. Mipi is more in mobile, but as things progress it will move into the industrial space. It is more complex to implement, so there could be another learning curve.”

Moving to higher resolutions will also lead to different manufacturing technologies, such as low-temperature polysilicon and indium gallium zinc oxide: “These have higher densities of pixels and thus higher resolution,” said Potts. “They are coming into consumer products and the rest of the market will follow in a few years.”

Limited resources

There is help available for companies with limited resources to implement display technology normally associated with larger projects. Express Logic for example has Guix, a graphical user interface development framework aimed at simplifying GUI development using ARM 32bit MCUs. “Guix reduces development times,” said Ken Maxwell, Guix Architect, “We have done a lot of the work, so you can save time. People do create their own graphics but it is difficult to make something as good as ours.”

The product is targeted at medical and white goods markets. “How fancy does the display on your washing machine have to be?” said Maxwell. “People have downloaded the demos and development kit but it has not led to anything released yet. There are some late in the development cycle. We know of products that are not too much longer away but we are not allowed to give details.” He said there was a long-term trend of graphics capabilities that once used sophisticated hardware now being implemented on small processors. “You once had the expensive graphics card in the PC,” he said. “A lot of these features are now available on a $5 ARM CPU.”

Another helper, this time for those who want to implement touchscreen technology, comes from Australian firm Splat Controls. The company specialises in making low-cost controllers for smaller products, a recent project being the controller for a cocktail mixing machine. “We are focused on the problem that people want the latest technology and shiny things and the current one is a touchscreen,” said Chief Executive Officer, David Stonier-Gibson. “Every man and his dog has a smartphone and people expect touchscreens with the same capabilities at the same cost as a smartphone. But nobody makes two million cocktail machines.”

So Splat’s aim is to create custom touchscreen displays for low volume markets, and it is doing this using a low-cost development chip from NXP; the LPC4088 Cortex-M4F based CPU with 512kB flash and 64kB RAM for firmware. External chips to support the display are an 8MB serial flash for images and fonts and 16MB RAM for screen buffering to give flicker-free switching between screens.

“We are aiming at getting a performance that will be sufficient for the task,” said Stonier-Gibson. “We have a guy in New Zealand making beer bottling machines for small breweries. He couldn’t have afforded a touchscreen and was using a toy PLC. When he saw ours, he tossed it out. We make colour touchscreens for people who would not otherwise be able to put it into their products.”

While technology is advancing to produce higher resolution displays with sophisticated touchscreen facilities, the user expectation for touchscreens on even basic products is leading many to look for low-cost alternatives to include in their products.